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Jasmonate is involved in the induction of tyrosine aminotransferase and tocopherol biosynthesis in Arabidopsis thaliana
Abstract
Coronatine-inducible tyrosine aminotransferase (TAT), which catalyses the transamination from tyrosine to p-hydroxyphenylpyruvate, is the first enzyme of a pathway leading via homogentisic acid to plastoquinone and tocopherols, the latter of which are known to be radical scavengers in plants. TAT can be also induced by the octadecanoids methyl jasmonate (MeJA) and methyl-12-oxophytodienoic acid (MeOPDA), as well as by wounding, high light, UV light and the herbicide oxyfluorfen. In order to elucidate the role of octadecanoids in the process of TAT induction in Arabidopsis thaliana (L.) Heynh., the jasmonate-deficient mutant delayed dehiscence (dde1) was used, in which the gene for 12-oxophytodienoic acid reductase 3 is disrupted. The amount of immunodetectable TAT was low. The enzyme was still fully induced by coronatine as well as by MeJA although induction by the latter was to a lesser extent and later than in the wild type. Treatment with MeOPDA, wounding and UV light, however, had hardly any effects. Tocopherol levels that showed considerable increases in the wild type after some treatments were much less affected in the mutant. However, starting levels of tocopherol were higher in non-induced dde1 than in the wild type. We conclude that jasmonate plays an important role in the signal transduction pathway regulating TAT activity and the biosynthesis of its product tocopherol.
... Both the regulation of jasmonates by vitamin E and vice versa have been shown to occur in model plants. On one hand, the role of jasmonates signalling on vitamin E biosynthesis has been demonstrated to occur in Arabidopsis thaliana (Sandorf and Holländer-Czytko 2002). The enzyme tyrosine aminotransferase (TAT), which is involved in the early steps of the tocopherol biosynthetic pathway to produce homogentisate, is induced at the mRNA and protein levels by methyl jasmonate (MeJA), methyl 12-oxo-phytodienoic acid (MeOPDA) and wounding (Lopukhina et al. 2001;Sandorf and Holländer-Czytko 2002). ...
... On one hand, the role of jasmonates signalling on vitamin E biosynthesis has been demonstrated to occur in Arabidopsis thaliana (Sandorf and Holländer-Czytko 2002). The enzyme tyrosine aminotransferase (TAT), which is involved in the early steps of the tocopherol biosynthetic pathway to produce homogentisate, is induced at the mRNA and protein levels by methyl jasmonate (MeJA), methyl 12-oxo-phytodienoic acid (MeOPDA) and wounding (Lopukhina et al. 2001;Sandorf and Holländer-Czytko 2002). The induction of TAT by MeJA occurred earlier and was induced more strongly than by MeOPDA and wounding. ...
... Even though the relationship between the antioxidant system and oxylipins is generally well accepted, the bidirectional link between them and its biological significance is not well established yet. On the one hand, oxylipin messenger compounds, including OPDA, JA and MeJA, have been demonstrated to induce antioxidant production, including both enzymatic antioxidants, such as superoxide dismutase and ascorbate peroxidase, and non-enzymatic, low-molecularweight antioxidant compounds, such as vitamin E, vitamin C and glutathione (Sandorf and Holländer-Czytko 2002;Sasaki-Sekimoto et al. 2005;Wolucka et al. 2005;Farooq et al. 2016). These findings highlight the importance of oxylipins signaling under stressful situations, in such a way that a positive feedback between antioxidants and lipid peroxidation-derived compounds contribute to maintain an adequate cellular redox homeostasis under stress. ...
Main conclusion
Jasmonic acid positively modulates vitamin E accumulation, but the latter can also partly influence the capacity to accumulate the jasmonic acid precursor, 12-oxo-phytodienoic acid, in white-leaved rockrose (Cistus albidus L.) plants growing in their natural habitat. This study suggests a bidirectional link between chloroplastic antioxidants and lipid peroxidation-derived hormones in plants.
Abstract
While vitamin E is well known for its antioxidant properties being involved in plant responses to abiotic stress, jasmonates are generally related to biotic stress responses in plants. Studying them in non-model plants under natural conditions is crucial for the knowledge on their relationship, which will help us to better understand mechanisms and limits of stress tolerance to implement better conservation strategies in vulnerable ecosystems. We studied a typical Mediterranean shrub, white-leaved rockrose (Cistus albidus) under natural conditions during three winters and we analyzed both α and γ-tocopherol, and the three main jasmonates forms 12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and jasmonoyl-isoleucine (JA-Ile). We found that JA contents positively correlated with vitamin E accumulation, most particularly with γ-tocopherol, the precursor of α-tocopherol (the most active vitamin E form). This finding was confirmed by exogenous application of methyl jasmonate (MeJA) in leaf discs under controlled conditions, which increased γ-tocopherol when applied at 0.1 mM MeJA and α-tocopherol at 1 mM MeJA. Furthermore, a complementary meta-analysis study with previously published reports revealed a positive correlation between JA and vitamin E, although this relationship turned to be strongly species specific. A strong negative correlation was observed, however, between total tocopherols and OPDA (a JA precursor located in chloroplasts). This antagonistic effect was observed between α-tocopherol and OPDA, but not between γ-tocopherol and OPDA. It is concluded that (i) variations in jasmonates and vitamin E due to yearly, inter-individual and sun orientation-driven variability are compatible with a partial regulation of vitamin E accumulation by jasmonates, (ii) vitamin E may also exert a role in the modulation of the biosynthesis of OPDA, with a much smaller effect, if any, on other jasmonates, and (iii) a trade-off in the accumulation of vitamin E and jasmonates might occur in the regulation of biotic and abiotic stress responses in plants.
... Likewise, there are different degrees of evidence on the regulatory role of phytohormones in the vitamin E biosynthetic pathway. In A. thaliana jasmonic acid (JA) promotes TYROSINE AMINOTRANSFERASE (TAT, Lopukhina et al. 2001, Sandorf andHolländer-Czytko 2002), and gibberellins (GAs) promote HPPD and -TMT transcriptional expression (Du et al. 2015). In non-model plants, JA, ethylene, abscisic acid (ABA) and GAs also promote the transcriptional expression of HPPD, HPT, TOCOPHEROL CYCLASE (TC) and -TMT (Falk et al. 2002, Munné-Bosch 2005, El Kayal et al. 2006, Chaudhary and Khurana 2009, Singh et al. 2011, Du et al. 2015. ...
... The rise of ChTAT expression levels increase the shikimate pathway flux through HPP and, consequently, HGA synthesis, which pool is limiting for vitamin E biosynthesis (DellaPenna andLast 2006, Zhang et al. 2013). However, it has been observed that TAT overexpression is not sufficient to significantly increase total tocopherol contents (Sandorf and Holländer-Czytko 2002). Indeed, to increase HGA production and vitamin E content in plant tissues, it is necessary not only to increase the pathway flux to HPP, but also to bypass the feedback inhibition of arogenate dehydrogenase by tyrosine (Rippert et al. 2004, Karunanandaa et al. 2005, DellaPenna and Last 2006) or reduce HGA catabolism by suppression of HGA dioxygenase (Stacey et al. 2016). ...
... It is likely that the role of JA in enhancing tocopherol levels is mediated through regulation of TAT and/or HPT in germinating C. humilis var. humilis seeds, since it has been observed that JA increase tocopherol contents by the upregulation of TAT levels in A. thaliana leaves (Sandorf and Holländer-Czytko 2002). ...
Vitamin E, a potent antioxidant either present in the form of tocopherols and/or tocotrienols depending on the plant species, tissue and developmental stage, plays a major role in protecting lipids from oxidation in seeds. Unlike tocopherols, which have a more universal distribution, the occurrence of tocotrienols is limited primarily to monocot seeds. Dwarf fan palm (Chamaerops humilis var. humilis) seeds accumulate tocotrienols in quiescent and dormant seeds, while tocopherols are de novo synthesized during germination. Here, we aimed to elucidate whether tocopherol biosynthesis is regulated at the transcriptional level during germination in this species. We identified and quantified the expression levels of five genes involved in vitamin E biosynthesis, including TYROSINE AMINOTRANSFERASE (ChTAT), HOMOGENTISATE PHYTYLTRANSFERASE (ChHPT), HOMOGENTISATE GERANYLGERANYL-TRANSFERASE (ChHGGT), TOCOPHEROL CYCLASE (ChTC) and TOCOPHEROL γ-METHYLTRANSFERASE (Chγ-TMT). Furthermore, we evaluated to what extent variations in the endogenous contents of hormones and hydrogen peroxide (H2O2) correlated with transcriptional regulation. Results showed an increase of ChTAT and ChHPT levels during seed germination, which correlated with an increase of jasmonic acid (JA), gibberellin4 (GA4), and H2O2 contents, while ChHGGT and Chγ-TMT expression levels decreased, thus clearly indicating vitamin E biosynthesis is diverted to tocopherols rather than to tocotrienols. Exogenous application of jasmonic acid increased tocopherol, but not tocotrienol content, thus confirming its regulatory role in vitamin E biosynthesis during seed germination. It is concluded that the biosynthesis of vitamin E is regulated at the transcriptional level during germination in dwarf fan palm seeds, with ChHPT playing a key role in the diversion of the vitamin E pathway towards tocopherols instead of tocotrienols.
... In higher plants, HPP is produced from tyrosine, which is catalyzed by tyrosine aminotransferase (TAT), which is influenced by various factors (e.g., jasmonic acid, octadecanoids, and caronatine) (Lopukhina et al., 2001;Sandorf and Holländer-Czytko, 2002). Exogenous application of these chemicals resulted in enhanced production of Toc due to elevated enzymatic activities (Lopukhina et al., 2001;Sandorf and Holländer-Czytko, 2002). ...
... In higher plants, HPP is produced from tyrosine, which is catalyzed by tyrosine aminotransferase (TAT), which is influenced by various factors (e.g., jasmonic acid, octadecanoids, and caronatine) (Lopukhina et al., 2001;Sandorf and Holländer-Czytko, 2002). Exogenous application of these chemicals resulted in enhanced production of Toc due to elevated enzymatic activities (Lopukhina et al., 2001;Sandorf and Holländer-Czytko, 2002). This HPP is then oxygenated to homogentisate (HGA) by the activity of HPP dioxigenase-the end product that merges with the end product (phytol diphosphate) from the MEP pathway. ...
... The biosynthesis of Toc is also influenced by phytohormones such as abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA). Jasmonic acid has been reported to regulate Toc biosynthesis genes in Arabidopsis and barley (Falk et al., 2002;Sandorf and Holländer-Czytko, 2002). Munné-Bosch and Alegre (2003) observed that enhanced endogenous SA can improve the synthesis of α-Toc in drought-stressed Phillyrea angustifolia. ...
... We found six groups of genes in the pathway significantly up-regulated-TAT, AOC3/AOC2/tynA, PPO, frmA/ ADH5/adhC, HPT/HGGT/ubiA, and maiA/CSTZ1 (Fig. 6). Previous work showed that TAT was induced by MeJA and wounding at both the RNA and protein level in Arabidopsis thaliana [65,66]. The TAT gene codes for the first enzyme in this biosynthetic pathway, which catalyzes the reaction from tyrosine to p-hydroxyphenylpyruvate, and is known to function as a radical scavenger, thus protecting plants under biotic and abiotic stress situations [66]. ...
... Previous work showed that TAT was induced by MeJA and wounding at both the RNA and protein level in Arabidopsis thaliana [65,66]. The TAT gene codes for the first enzyme in this biosynthetic pathway, which catalyzes the reaction from tyrosine to p-hydroxyphenylpyruvate, and is known to function as a radical scavenger, thus protecting plants under biotic and abiotic stress situations [66]. ...
Background
Bilberry (Vaccinium myrtillus L.) is one of the most abundant wild berries in the Northern European ecosystems. This species plays an important ecological role as a food source for many vertebrate and invertebrate herbivores. It is also well-recognized for its bioactive compounds, particularly substances involved in natural defenses against herbivory. These defenses are known to be initiated by leaf damage (e.g. chewing by insects) and mediated by activation of the jasmonic acid (JA) signaling pathway. This pathway can be activated by exogenous application of methyl jasmonate (MeJA), the volatile derivative of JA, which is often used to stimulate plant defense responses in studies of plant-herbivore interactions at ecological, biochemical, and molecular organismal levels. As a proxy for herbivore damage, wild V. myrtillus plants were treated in the field with MeJA and changes in gene expression were compared to untreated plants.
Results
The de novo transcriptome assembly consisted of 231,887 unigenes. Nearly 71% of the unigenes were annotated in at least one of the databases interrogated. Differentially expressed genes (DEGs), between MeJA-treated and untreated control bilberry plants were identified using DESeq. A total of 3590 DEGs were identified between the treated and control plants, with 2013 DEGs upregulated and 1577 downregulated. The majority of the DEGs identified were associated with primary and secondary metabolism pathways in plants. DEGs associated with growth (e.g. those encoding photosynthesis-related components) and reproduction (e.g. flowering control genes) were frequently down-regulated while those associated with defense (e.g. encoding enzymes involved in biosynthesis of flavonoids, lignin compounds, and deterrent/repellent volatile organic compounds) were up-regulated in the MeJA treated plants.
Conclusions
Ecological studies are often limited by controlled conditions to reduce the impact of environmental effects. The results from this study support the hypothesis that bilberry plants, growing in natural conditions, shift resources from growth and reproduction to defenses while in a MeJA-induced state, as when under insect attack. This study highlights the occurrence of this trade-off at the transcriptional level in a realistic field scenario and supports published field observations wherein plant growth is retarded and defenses are upregulated.
... Jasmonoyl-isoleucine is an important plant messenger that regulates, for example, expression of genes involved in plant defence (Berger 2002, Halitschke and Baldwin 2003, Devoto and Turner 2005 response to pathogen and insect attack and can act as a messenger independently of JA and JA-Ile (Danon et al. 2005, Taki et al. 2005 the dry season, while JA and JA-Ile levels remained unaltered. JA, but not OPDA, has been shown to induce tyrosine aminotransferase activity, thereby increasing biosynthesis of tocopherols ( Sandorf and Holländer-Czytko 2002 relative evidence that ABA, rather than jasmonates, induces vitamin 10 Morales et al. Tree Physiology Online at http://www.treephys.oxfordjournals.org ...
... Inicialment, l'exposició a l'estrès abiòtic (per exemple, dèficit hídric) augmenta de forma transitòria la producció d'hidroperòxids lipídics i, en conseqüència, d'oxilipines, probablement pel fet que les concentracions d'antioxidants existents a l'inici són insuficients per detoxificar les ROS. La pròpia producció d'oxilipines desencadena, posteriorment, una regulació a l'alça de la producció d'antioxidants a través d'un circuit de retroalimentació, com per exemple la vitamina E de la que ha estat descrita la inducció de la seva biosíntesi pels jasmonats (Sandorf & Holländer-Czytko, 2002). Finalment, l'augment de les concentracions d'antioxidants, en aquest cas de vitamina E suprimeix la producció d'oxilipines, mitjançant l'eliminació de ROS i detoxificació del radicals lipídics peroxil. ...
One of the most accepted theories of ageing in animals and humans is the free radical theory of ageing, which describes that oxidative stress increases with age. Unfortunately, there are very few studies that test this theory in plants, and none in long-lived perennial plants. In this thesis, we choose two models of long-lived perennial plants to investigate the processes of ageing and the importance of oxidative stress, along with the role of protection mechanisms such as vitamin E, in the ageing process in plants under natural climatic conditions. With this aim, we explored the effects of age (ranging from 1 to 280 years) in the extent of lipid peroxidation, photoprotection mechanisms and other oxidative stress markers in leaves and tubers (perennial organ) in the longest-lived perennial – not clonal – herb registered to date, Borderea pyrenaica.
The other species used in the study, Vellozia gigantea, is an endemic plant of Brazil in which it is not possible estimate its age, but it is considered to live more than 500 years. In this species, we evaluated the effect of size on various oxidative stress markers and evaluated the ecophysiological response to seasonal variations in water availability (rainy and dry season) in plants grown in their natural habitat. Results show that neither age nor size have a negative effect on plant physiological processes related to oxidative stress, thus suggesting that the free radical theory of ageing is not universal in perennials plants. B. pyrenaica showed absence of physiological deterioration with aging as indicated by oxidative stress markers, at least until the studied age (280 years), showing that the oldest females display a greater photoprotection than males of the same age and juveniles (negative senescence). The perennial organ that growsunderground in B. pyrenaica (tubers) seems to be the secret of its long life, considering its unique growth strategy together with its efficient antioxidant protection mechanism (vitamin E), whose levels increased with age. V. gigantea also shows absence of physiological deterioration with ageing (mature individuals of various sizes were examined), which was also associated with increasing vitamin E levels in the oldest individuals, suggesting therefore a case of negligible senescence. In this plant species, tocotrienols were found in leaves (this is the first documented study showing tocotrienols in leaves of higher plants), which might have an important role to protect against photo-oxidative stress, along with tocopherols. Water deficit conditions during the dry season led V. gigantea to activate an efficient protection mechanism based on abscisic acid-induced stomatal closure to prevent water loss and presumably increase vitamin E biosynthesis. In this thesis, it is concluded that perennials plants are highly resistant organisms to stress and ageing, as shown by their protective mechanisms to maintain adequate physiological functions until very advanced ages, so that neither age nor size cause any functional decline in the organism.
... Plants under metal toxicity such as that of Al, Ni, Cu and Cd when treated with brassinosteroids (BRs) showed initial induction of H 2 O 2 that resulted in the transduction of signals that caused an increase in the expression of genes coding for antioxidants including GR, CAT, SOD, GPX, APX, ascorbate, glutathione, tocopherols, carotenoids and proline (Bajguz and Hayat 2009;Xia et al. 2009;Fariduddin et al. 2014). D. A. Khan et al. babarmustafeez@gmail.com Similarly, Jasmonates (JAs) increase the expression of genes that leads to the formation and accretion of ascorbate, glutathione and tocopherols in metal-stressed plants (Sandorf and Holländer-Czytko 2002;Sasaki-Sekimoto et al. 2005). Methyl jasmonate treatment in low concentration in Cd stressed plant showed increase in levels of SOD, APX, CAT, ascorbic acid and dehydro ascorbic acid (DHA) along with decrease in H 2 O 2 and lipid peroxidation (Yan et al. 2013;Keramat et al. 2009;Chen et al. 2014). ...
... It is produced inside chloroplasts and protoplastids and is located in membranes of cell and organelles where it protects membrane lipids from peroxidation (Jaleel et al. 2009). Under oxidative stress and hormonal influence (such as that of jasmonates), expression of genes encoding the tocopherol synthesis significantly increases that leads to enhanced biosynthesis of tocopherols (Sandorf and Holländer-Czytko 2002). It scavenges oxygen free radicals, singlet oxygen ( 1 O 2 ) and lipid peroxy radicals (by acting as chain reaction terminator in lipid autoxidation). ...
A number of factors adversely affect the plant health and, ultimately, the agricultural yield. Various abiotic stress factors including temperature variation, flooding, salinity, drought, nutrient depletion and environmental toxicities cause significant losses annually. Among these, metal and metalloid toxicity results in physiological, morphological and metabolic alteration in plant body. Mediated through various mechanisms, these ions result in early cell death. The oxidative stress, owing to the production of various reactive oxygen species is the most important contributing agent. Phytohormones produced by plants help to counteract the effects of these stress factors. Through a number of enzymatic and non-enzymatic pathways, they regulate the antioxidant pathways in the plant body. The study of these phytohormones can help in developing an understanding of the metabolic processes and can help in providing important checkpoints for employing interventional strategies to enhance the antioxidant potential of metal-stressed plants. This chapter summarizes the role of various phytohormones in the antioxidant response to metal stress. Moreover, various mechanisms that are employed by the plants to enhance their antioxidant potential have been discussed. Towards the end, the regulation of phytohormone-mediated antioxidation has been provided.
... It results mainly from the significantly lower concentrations of α-tocopherol and γ-tocopherol in the BR mutants with respect to the 'Bowman' cultivar. It is known that biosynthesis of tocopherols is regulated by the stress hormones: ABA, JA and SA (Sandorf and Hollander-Czytko 2002, Munne-Bosch and Penuelas 2003, Munne-Bosch 2005, Szarka et al. 2012), however to the best of our knowledge, up to now an involvement of endogenous BRs in regulation of the tocopherol biosynthesis has not been reported. Our study indicates that functional mechanisms of BR biosynthesis and signaling are crucial for normal accumulation of tocopherols under the control conditions in barley. ...
... It is known that the tocopherol biosynthesis is regulated at its early stage by JA (Falk et al. 2002, Sandorf andHollander-Czytko 2002). It was reported in our previous study that under the control conditions the analyzed NILs (both BR-deficient and BR-insensitive) accumulated significantly lower concentrations of JA when compared with the 'Bowman' cultivar ). ...
Drought is one of the most adverse stresses that affect plant growth and yield. Disturbances in metabolic activity resulting from drought cause overproduction of reactive oxygen species (ROS). It is postulated that brassinosteroids (BRs) regulate plant tolerance to the stress conditions, but the underlying mechanisms remain largely unknown. An involvement of endogenous BRs in regulation of the antioxidant homeostasis is not fully clarified either. Therefore, the aim of this study was to elucidate the role of endogenous BRs in regulation of non-enzymatic antioxidants in barley (Hordeum vulgare) under control and drought conditions. The plant material included the ‘Bowman’ cultivar and a group of semi-dwarf near-isogenic lines (NILs), representing mutants deficient in BR biosynthesis or signaling. In general, accumulations of eleven compounds representing various types of non-enzymatic antioxidants were analyzed under both conditions. The analyses of accumulations of reduced and oxidized forms of ascorbate indicated that the BR mutants contain significantly higher contents of dehydroascorbic acid under drought conditions when compared with the ‘Bowman’ cultivar. The analysis of glutathione accumulation indicated that under the control conditions the BR-insensitive NILs contained significantly lower concentrations of this antioxidant when compared with the rest of genotypes. Therefore, we postulate that BR sensitivity is required for normal accumulation of glutathione. A complete accumulation profile of various tocopherols indicated that functional BR biosynthesis and signaling are required for their normal accumulation under both conditions. Results of this study provided an insight into the role of endogenous BRs in regulation of the non-enzymatic antioxidant homeostasis.
... The level of tocopherols, as well as that of other antioxidants in plants usually increases in response to a particular stress factor, which stimulates the production of ROS and is mediated by the action of phytohormones (jasmonic acid, abscisic acid). The promotion of POL leads to the formation of jasmonic acid -phytohormone that activates the expression of nuclear genes encoding enzymes of tocopherol synthesis [41,42]. However, strengthening of photo-and antioxidant protection in the cell may be insufficient for the plant could bear unfavorable conditions and does not stop its ageing. ...
... For example, tocopherols as intermediates participate in modulation of expression of jasmonatedependent genes, which are usually activated during ageing and damaged by pathogens (Fig. 3) [41]. Thus, if propagation of POL does not stop as a result of antioxidant action of membrane localized tocopherols, jasmonic acid level is increased. ...
Tocopherol synthesis has only been observed in photosynthetic organisms (plants, algae and some cyanobacteria). Tocopherol is synthesized in the inner membrane of chloroplasts and distributed between chloroplast membranes, thylakoids and plastoglobules. Physiological significance of tocopherols for human and animal is well-studied, but relatively little is known about their function in plant organisms. Among the best characterized functions oftocopherols in cells is their ability to scavenge and quench reactive oxygen species and fat-soluble by-products of oxidative stress. There are the data on the participation of different mechanisms of α-tocopherol action in protecting photosystem II (PS II) from photoinhibition both by deactivation of singlet oxygen produced by PSII and by reduction of proton permeability of thylakoid membranes, leading to acidification of lumen under high light conditions and activation of violaxanthin de-epoxidase. Additional biological activity of tocopherols, independent of its antioxidant functions have been demonstrated. Basic mechanisms for these effects are connected with the modulation of signal transduction pathways by specific tocopherols and, in some instances, by transcriptional activation of gene expression.
... Similarly, the specific regulation of vitamin E by ABA and JA during the dehydration of B. graminifolia enhances protection against photooxidation. Regulation of vitamin E biosynthesis by ABA and jasmonates has been proposed in several studies for other species (Sandorf and Holländer-Czytko, 2002;El Kayal et al., 2006;Siles et al., 2018;Villadangos and Munne-Bosch, 2023). The increase in a-tocopherol in thylakoids has been proposed to provide photoprotection by scavenging free radicals and 1 O 2 , thereby exerting a synergic effect with other antioxidants. ...
Desiccation tolerance in vegetative tissues enables resurrection plants to remain quiescent under severe drought and rapidly recover full metabolism once water becomes available. Barbacenia graminifolia is a resurrection plant that occurs at high altitudes, typically growing on rock slits, exposed to high irradiance and limited water availability. We analyzed the levels of reactive oxygen species (ROS) and antioxidants, carotenoids and its cleavage products, and stress-related phytohormones in fully hydrated, dehydrated, and rehydrated leaves of B. graminifolia. This species exhibited a precise adjustment of its antioxidant metabolism to desiccation. Our results indicate that this adjustment is associated with enhanced carotenoid and apocarotenoids, a-tocopherol and compounds of ascorbate-glutathione cycle. While a-carotene and lutein increased in dried-leaves suggesting effective protection of the light-harvesting complexes, the decrease in b-carotene was accompanied of 10.2-fold increase in the content of b-cyclocitral, an apocarotenoid implicated in the regulation of abiotic stresses, compared to hydrated plants. The principal component analysis showed that dehydrated plants at 30 days formed a separate cluster from both hydrated and dehydrated plants for up to 15 days. This regulation might be part of the protective metabolic strategies employed by this resurrection plant to survive water scarcity in its inhospitable habitat.
... After the generation of linolenic (18:3) and linoleic (18:2) peroxyl radicals', these undergo a cascade of reactions, thereby, leading to the generation of MDA and other signaling molecules as jasmonic acid (JA) (Farmer 2007). Jasmonic acid is known to be associated with the regulation of hydroxyphenolpyruvate dioxygenase (HPPD) enzyme of tocopherol biosynthetic pathway (Sandorf and Czytko 2002), indicating its participation in cell signaling. Tocopherols protect fatty acids from lipid peroxidation in plastids by efficiently scavenging lipid peroxyl radicals and quenching ROS (Leng et al. 2015;Broznić et al. 2016;Boonnoy et al. 2017;Fritsche et al. 2017). ...
The changing global climate have given rise to abiotic stresses that adversely affect the metabolic activities of plants, limit their growth, and agricultural output posing a serious threat to food production. The abiotic stresses commonly lead to production of reactive oxygen species (ROS) that results in cellular oxidation. Over the course of evolution, plants have devised efficient enzymatic and non-enzymatic anti-oxidative strategies to counteract harmful effects of ROS. Among the emerging non-enzymatic anti-oxidative technologies, the chloroplast lipophilic antioxidant vitamin A (Tocopherol) shows great promise. Working in coordination with the other cellular antioxidant machinery, it scavenges ROS, prevents lipid peroxidation, regulates stable cellular redox conditions, simulates signal cascades, improves membrane stability, confers photoprotection and enhances resistance against abiotic stresses. The amount of tocopherol production varies based on the severity of stress and its proposed mechanism of action involves arresting lipid peroxidation while quenching singlet oxygen species and lipid peroxyl radicals. Additionally, studies have demonstrated its coordination with other cellular antioxidants and phytohormones. Despite its significance, the precise mechanism of tocopherol action and signaling coordination are not yet fully understood. To bridge this knowledge gap, the present review aims to explore and understand the biosynthesis and antioxidant functions of Vitamin E, along with its signal transduction and stress regulation capacities and responses. Furthermore, the review delves into the light harvesting and photoprotection capabilities of tocopherol. By providing insights into these domains, this review offers new opportunities and avenues for using tocopherol in the management of abiotic stresses in agriculture.
... Moreover, it has been revealed that α-tocopherols can increase the tolerance of tomatoes to TMV infection [35]. Tyrosine aminotransferase (TAT), which catalyzes the transamination from tyrosine to p-hydroxyphenylpyruvate, is the first enzyme in a pathway from homogentisic acid to tocopherols [36,37]. ...
Maize lethal necrosis (MLN), one of the most important maize viral diseases, is caused by maize chlorotic mottle virus (MCMV) infection in combination with a potyvirid, such as sugarcane mosaic virus (SCMV). However, the resistance mechanism of maize to MLN remains largely unknown. In this study, we obtained isoform expression profiles of maize after SCMV and MCMV single and synergistic infection (S + M) via comparative analysis of SMRT- and Illumina-based RNA sequencing. A total of 15,508, 7567, and 2378 differentially expressed isoforms (DEIs) were identified in S + M, MCMV, and SCMV libraries, which were primarily involved in photosynthesis, reactive oxygen species (ROS) scavenging, and some pathways related to disease resistance. The results of virus-induced gene silencing (VIGS) assays revealed that silencing of a vitamin C biosynthesis-related gene, ZmGalDH or ZmAPX1, promoted viral infections, while silencing ZmTAT or ZmNQO1, the gene involved in vitamin E or K biosynthesis, inhibited MCMV and S + M infections, likely by regulating the expressions of pathogenesis-related (PR) genes. Moreover, the relationship between viral infections and expression of the above four genes in ten maize inbred lines was determined. We further demonstrated that the exogenous application of vitamin C could effectively suppress viral infections, while vitamins E and K promoted MCMV infection. These findings provide novel insights into the gene regulatory networks of maize in response to MLN, and the roles of vitamins C, E, and K in conditioning viral infections in maize.
... Vitamin E concentrations have been reported to increase under stress conditions 36,57 and chlorophyll degradation and phytol recycling induce vitamin E biosynthesis. 58 Particularly, herbivoremediated damage results in jasmonate accumulation 59 and activation of jasmonate-mediated signaling pathways 60cellular mechanisms that have been reported to increase tocopherol concentrations in plant cells 61,62 and might explain the observed higher concentrations of vitamin E in damaged leaves (Fig. 2). ...
BACKGROUND
Local leafy vegetables are gaining attention as affordable sources of micronutrients, including vitamins, pro‐vitamin carotenoids and other bioactive compounds. Stinging nettles (Urtica spp.) are used as source of fibers, herbal medicine and food. However, despite the relatively wide geographical spread of Urtica leptophylla on the American continent, little is known about its content of vitamin E congeners and carotenoids. We therefore investigated the particular nutritional potential of different plant structures of wild Costa Rican U. leptophylla by focusing on their vitamin E and carotenoid profiles.
RESULTS
Young, mature and herbivore‐damaged leaves, flowers, stems and petioles were collected and freeze‐dried. Vitamin E and carotenoids were determined by high‐performance liquid chromatography after liquid/liquid extraction with hexane. α‐Tocopherol was the major vitamin E congener in all structures. Flowers had a high content of γ‐tocopherol. Herbivore‐damaged leaves had higher contents of vitamin E than undamaged leaves. Lutein was the major and β‐carotene the second most abundant carotenoid in U. leptophylla. No differences in carotenoid profiles were observed between damaged and undamaged leaves.
CONCLUSION
The leaves of U. leptophylla had the highest nutritional value of all analyzed structures; therefore, they might represent a potential source of α‐tocopherol, lutein and β‐carotene. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... Malate dehydrogenase (MDH) oxidize oxaloacetic acid to malate and also enhances plant stress tolerance (Wu et al., 2007). Tyrosine aminotransferase (TAT) catalyzes the biosynthesis of the free radical scavenger vitamin E (Sandorf and Holländer-Czytko, 2002). Here, the foregoing genes were upregulated by over twofold in response to selenite fertilization but by not more than twofold following selenate supplementation. ...
Certain tea plants (Camellia sinensis) have the ability to accumulate selenium. In plants, the predominant forms of bioavailable Se are selenite (SeO32–) and selenate (SeO42–). We applied transcriptomics and proteomics to hydroponically grown plants treated with selenite or selenate for 48 h in the attempt to elucidate the selenium absorption and assimilation mechanisms in tea. A total of 1,844 differentially expressed genes (DEGs) and 691 differentially expressed proteins (DEPs) were obtained by comparing the Na2SeO3 and Na2SeO4 treatments against the control. A GO analysis showed that the genes related to amino acid and protein metabolism and redox reaction were strongly upregulated in the plants under the Na2SeO3 treatment. A KEGG pathway analysis revealed that numerous genes involved in amino acid and glutathione metabolism were upregulated, genes and proteins associated with glutathione metabolism and ubiquinone and terpenoid-quinone biosynthesis were highly expressed. Genes participating in DNA and RNA metabolism were identified and proteins related to glutathione metabolism were detected in tea plants supplemented with Na2SeO4. ABC, nitrate and sugar transporter genes were differentially expressed in response to selenite and selenate. Phosphate transporter (PHT3;1a, PHT1;3b, and PHT1;8) and aquaporin (NIP2;1) genes were upregulated in the presence of selenite. Sulfate transporter (SULTR1;1 and SULTR2;1) expression increased in response to selenate exposure. The results of the present study have clarified Se absorption and metabolism in tea plants, and play an important theoretical reference significance for the breeding and cultivation of selenium-enriched tea varieties.
... After Linoleic (18:2) and linolenic (18:3) Peroxyl radicals' formation, these go through a series of reactions which leads to the formation of MDA and other signaling molecules including jasmonic acid (JA) (Farmer 2007). JA is believed to be involved in the regulation of HPPD enzyme of Tocopherol biosynthesis pathway (Sandorf and Holländer-Czytko 2002), showing the involvement of Tocopherols in cell signaling (Fig. 3B). The antioxidative properties of Tocopherols are due to their ability to scavenge lipid peroxyl radicals and quench ROS, so protecting fatty acids from lipid peroxidation (Boonnoy et al. 2017;Broznic et al. 2016;Fritsche et al. 2017;Leng et al. 2015). ...
Tocopherols are vitamin E group of lipophilic antioxidant compounds, exclusively synthesized by plants. Mutant and transgenic approaches with loss or gain of function of Tocopherol pathway genes tends to provide insight into the role of this compound in plants. Tocopherols show fluctuation in their quantity under abiotic stresses, suggesting their critical role as antioxidant and as an indicator of stress tolerance in plants. From genetic approaches, it has been revealed that Tocopherols’ function is beyond antioxidant activities, as in some cases, it plays a major role in cell signaling as well. Though there is a lot of literature available about the enzymes function in the Tocopherol biosynthesis, but still the underlying mechanisms that regulate the entire pathway and fluctuation in Tocopherol content and composition during stress conditions remain less understood in plants. Understanding the induction mechanism under stress will help to develop methods to engineer plants with high Tocopherol contents. The main aim of this review is to reveal the responses of important Tocopherol biosynthesis enzymes under abiotic stresses to advance our genetic approaches and tools to unravel the functional mystery of Tocopherols in plants. In addition, the role of Tocopherols in cell signaling is also described in detail.
... However, similar numbers of genes related to vitamin E biosynthesis were identified between E. guineensis (37) and G. max (39), which is interesting as both species have high vitamin E content. In E. guineensis, a significant expansion of the EgTAT gene family (17 copies) was detected relative to A. thaliana (3) [98], O. sativa (3), Z. mays (3), and G. max (5), which may suggest a higher efficiency of tyrosine transformation to p-hydroxyphenyl-pyruvate in oil palm. ...
Vitamin E is essential for human health and plays positive roles in anti-oxidation. Previously, we detected large variation in vitamin E content among 161 oil palm accessions. In this study, twenty oil palm accessions with distinct variation in vitamin E contents (171.30 to 1 258.50 ppm) were selected for genetic variation analysis and developing functional markers associated with vitamin E contents. Thirty-seven homologous genes in oil palm belonging to vitamin E biosynthesis pathway were identified via BLASTP analysis, the lengths of which ranged from 426 to 25 717 bp (average 7 089 bp). Multiplex PCR sequencing for the 37 genes found 1 703 SNPs and 85 indels among the 20 oil palm accessions, with 226 SNPs locating in the coding regions. Clustering analysis for these polymorphic loci showed that the 20 oil palm accessions could be divided into five groups. Among these groups, group I included eight oil palm accessions whose vitamin E content (mean value: 893.50 ppm) was far higher than other groups (mean value 256.29 to 532.94 ppm). Correlation analysis between the markers and vitamin E traits showed that 134 SNP and 7 indel markers were significantly ( p < 0.05) related with total vitamin E content. Among these functional markers, the indel EgTMT-1-24 was highly correlated with variation in vitamin E content, especially tocotrienol content. Our study identified a number of candidate function associated markers and provided clues for further research into molecular breeding for high vitamin E content oil palm.
... In Arabidopsis (Arabidopsis thaliana (L.) Heynh.) wurde gezeigt, dass das Phytohormon Jasmonsäure, das die Seneszenz von Pflanzengeweben fördern kann, die Expression einer Tyrosin-Aminotransferase (TAT) erhöhen kann, was eine Akkumulation von γ-Tocopherol verursachte(Sandorf & Holländer-Czytko 2002).Falk et al. (2002) berichteten, dass in Gerste die Transkriptmenge der 4-Hydroxyphenylpyruvat-Dioxygenase (HPD) stieg, nachdem Blätter extern mit Methyljasmonat, einem Methylester der Jasmonsäure, versorgt wurden, dem Phytohormon Ethen ausgesetzt wurden oder direkt oxidative Schäden durch Applikation von H2O2 induziert wurden. Auch in Mangopflanzen (Mangifera indica L.) konnte gezeigt werden, dass die HPD-Aktivität durch Ethen induziert werden kann, was laut Singh et al. (2011) direkt in einem Anstieg des Tocopherolgehalts in Blättern resultierte. ...
Der Klimawandel birgt viele gesellschaftliche Herausforderungen. Zweifellos stellen die zunehmenden Wetterextreme auch für Nutzpflanzen eine große Herausforderung dar. Um den Nahrungs- und Futtermittelbedarf der wachsenden Weltbevölkerung zu decken, sollen sie auch in Zukunft hohe Erträge liefern. Ein Faktor, der entscheidend sein wird, dass die Landwirtschaft auch unter den sich abzeichnenden Umweltbedingungen stabile Erträge generieren kann, ist die Entwicklung von neuen Pflanzensorten, die besser mit den widrigen Wachstumsbedingungen umgehen können. Um die Entwicklung von neuen Gerstensorten (Hordeum vulgare L.) zu unterstützen, sollten molekulare und physiologische Reaktionen von Gerstenpflanzen untersucht werden, die förderlich für die Vitalität und Ausdauer der Pflanzen unter Trockenstress sein könnten. Zu diesem Zweck wurde ein Set genetisch vielfältiger Gerstengenotypen in einem Rollgewächshaus (RGH) angebaut. Die Pflanzen wuchsen unter feldnahen Bedingungen sowohl unter hoher als auch unter dauerhaft reduzierter Wasserverfügbarkeit. Im ersten Teil dieser Arbeit wurden die Pflanzen auf den Gehalt von Tocopherol und Tocotrienol getestet. In Biomembranen können diese, auch als Vitamin E bezeichneten, lipophilen Verbindungen, die Ausbreitung der Lipidperoxidation verhindern, die insbesondere bei oxidativem Stress auftreten kann. Dies wurde bereits als vorteilhaft für das Wachstum von Pflanzen unter diversen abiotischen Stressszenarien beschrieben. Vorangegangene genomweite Assoziationsstudien (GWAS) deuteten darauf hin, dass eine Homogentisat-Phytyltransferase (HPT-7H) und eine Homogentisat-Geranylgeranyltransferase (HGGT), zwei Gene der Vitamin E Biosynthese auf Chromosom 7H, signifikant die Akkumulation von Vitamin E in Blättern respektive Körnern beeinflussen können. Die Identifikation von allelischen Variationen beider Gene, die mit hohen oder niedrigen Mengen an Vitamin E in verschiedenen Geweben in Verbindung standen, bestätigten diese Vermutungen. Auch abhängig von den verschiedenen Allelen, wurde in Blättern durch Trockenheit die Akkumulation von HPT-7H-Transkripten induziert, und somit proportional die Akkumulation von Tocopherolen. Auf Grundlage der gesammelten Informationen können genetische Marker konstruiert werden, die bei der markerassistierten Züchtung von Gerstensorten eingesetzt werden können, welche einen höheren Vitamin E Gehalt aufweisen und gegenüber oxidativen Schäden toleranter sein können. Im zweiten Teil dieser Arbeit wurde das Blatttranskriptom von acht ausgewählten Gerstensorten analysiert. Vier dieser Genotypen wiesen eine hohe und vier eine niedrige Ertragsstabilität unter Trockenstress auf. Die Ertragsstabilität wurde als repräsentatives Maß für die Fitness der Pflanzen gewählt. Globale Transkriptomanalysen sollten einen Einblick in multiple molekulare und physiologische Reaktionen der Pflanzen ermöglichen, die durch ungünstige Wachstumsbedingungen hervorgerufen werden. Es gab Anzeichen, dass die Pflanzen im RGH keinen Trockenschock erlitten. Der im RGH graduell und anhaltend applizierte Trockenstress dürfte besonders gut geeignet gewesen sein, die Reaktionen von Pflanzen abzuschätzen, die auch beim Anbau im Feld unter Wassermangel auftreten. Für jeden Genotyp wurden Gene identifiziert, die differentiell durch Trockenstress exprimiert waren. Im Rahmen dieser Arbeit wurden in erster Linie Gene betrachtet, die in mehreren Genotypen auf den Trockenstress reagierten. Eine geteilte Antwort multipler Genotypen deutet auf eine besonders konservierte Funktion hin, die womöglich besonders relevant für die Adaption an den Stress sein könnte. Zunächst wurden die Gene betrachtet, die in allen acht Genotypen differentiell durch den Wassermangel reguliert wurden. Anschließend wurden Gene betrachtet, die nur spezifisch in allen vier ertragsstabilen oder spezifisch in allen vier ertragsinstabilen Genotypen differentiell exprimiert wurden. Es fanden sich nur wenige Gene, die den beiden letzten Kriterien entsprachen. Um weitere Gene zu identifizieren, die einen Unterschied in den trockensensitiven und toleranten Genotypen vermitteln könnten, wurden Gene identifiziert, deren Aktivität mit der Ertragsstabilität in Verbindung stand. Somit wurden Gene betrachtet, die zwischen den verschiedenen Genotypen differentiell reguliert waren. Im Allgemeinen war keines dieser Gene durch den Trockenstress reguliert. In einigen Fällen konnte die Aktivität dieser Gene mit verschiedenen Allelen in Verbindung gebracht werden. Es wird davon ausgegangen, dass die genotypspezifische Aktivität dieser Gene den physiologischen Zustand der Pflanzen unabhängig von den betrachteten Wachstumsbedingungen beeinflusste. Die ausgelösten metabolischen Veränderungen ermöglichten den ertragsstabilen Pflanzen womöglich besser auf den Wassermangel zu reagieren. Für einige der identifizierten Gene wurde der mögliche Einfluss auf die Trockenadaption im Kontext der molekularen Funktion diskutiert. Darunter waren eine Reihe von Genen, die intrazelluläre Signalkaskaden beeinflussen könnten und somit auch die Expression weiterer Gene. Dies wurde auch für einige Gene vermutet, die an der Wahrnehmung und Biosynthese von Pflanzenhormonen beteiligt sind. Darüber hinaus gab es Grund zur Annahme, dass die Pflanzen die Aktivität zentraler N- und C-Stoffwechselwege als Reaktion auf Stress veränderten. Dabei wiesen trockentolerante Genotypen womöglich eine höhere Rate der Zellatmung auf. Eine effektivere Energiegewinnung könnte bei der Bewältigung von Trockenstress von Vorteil sein. Eine dauerhaft erhöhte Rate der Zellatmung könnte jedoch mit generell niedrigeren Ertragsleistungen in Verbindung stehen. Auf Grundlage von technischen und biologischen Validierungen der Expressionswerte wurde bewertet, ob die gefundenen regulatorischen Merkmale eine geeignete Grundlage für künftigen Ansätze darstellen könnten, die Trockenanpassung von Gerste zu studieren.
... The compatible Psm and the HR-inducing Psm avRpm1 strain triggered 590 tocopherol accumulation, suggesting that both PTI and ETI might be involved in the 591 activation of tocopherol biosynthesis (Fig. 3). Analyses of Arabidopsis mutants impaired 592 in biotic stress-related hormonal pathways indicate that the P. syringae-triggered 593 induction of tocopherol biosynthesis largely proceeds independently of the SA-, NHP-, 594 23 been previously implicated in the UV light-and drought stress-induced tocopherol 596 production, respectively (Sandorf and Holländer-Czytko, 2002;Cela et al., 2009). ...
Tocopherols are lipid-soluble antioxidants synthesized in plastids of plants and other photosynthetic organisms. The four known tocopherols, α-, β-, γ-, and δ-tocopherol, differ in number and position of methyl groups on their chromanol head group. In unstressed Arabidopsis (Arabidopsis thaliana) leaves, α-tocopherol constitutes the main tocopherol form, whereas seeds predominantly contain γ-tocopherol. Here, we show that inoculation of Arabidopsis leaves with the bacterial pathogen Pseudomonas syringae induces the expression of genes involved in early steps of tocopherol biosynthesis and triggers strong accumulation of γ-tocopherol, moderate production of δ-tocopherol, and generation of the benzoquinol precursors of tocopherols. The pathogen-inducible biosynthesis of tocopherols is promoted by the immune regulators ENHANCED DISEASE SUSCEPTIBILITY1 and PHYTOALEXIN-DEFICIENT4. In addition, tocopherols accumulate in response to bacterial flagellin and reactive oxygen species. By quantifying tocopherol forms in inoculated wild-type plants and biosynthetic pathway mutants, we provide biochemical insights into the pathogen-inducible tocopherol pathway. Notably, vitamin E deficient2 (vte2) mutant plants, which are compromised in both tocopherol and benzoquinol precursor accumulation, exhibit increased susceptibility toward compatible P. syringae and possess heightened levels of markers of lipid peroxidation after bacterial infection. The deficiency of triunsaturated fatty acids in vte2-1 fatty acid desaturase3-2 (fad3-2) fad7-2 fad8 quadruple mutants prevents increased lipid peroxidation in the vte2 background and restores pathogen resistance to wild-type levels. Therefore, the tocopherol biosynthetic pathway positively influences salicylic acid accumulation and guarantees effective basal resistance of Arabidopsis against compatible P. syringae, possibly by protecting leaves from the pathogen-induced oxidation of trienoic fatty acid-containing lipids.
... Interestingly, the higher plastochromanol-8 content was observed in parallel with higher JA content in Pepton-treated plants exposed to water stress. Since jasmonates can increase the expression of the gene encoding tyrosine aminotransferase (Sandorf and Holländer-Czytko, 2002), which is involved in the biosynthesis of homogentisate, it is likely that Pepton-related effects on jasmonates may exert a positive effect on platochromanol-8 accumulation. Additionally, the content of tyrosine (1.92%) in Pepton can partially explain the increase observed in tococromanols. ...
Biostimulants may promote growth or alleviate the negative effects of abiotic stress on plant growth eventually resulting in enhanced yields. We examined the mechanism of action of an enzymatically hydrolyzed animal protein-based biostimulant (Pepton), which has previously been shown to benefit growth and yield in several horticultural crops, particularly under stressful conditions. Tomato plants were exposed to well-watered and water-stressed conditions in a greenhouse and the hormonal profiling of leaves was measured during and after the application of Pepton. Results showed that the Pepton application benefited antioxidant protection and exerted a major hormonal effect in leaves of water-stressed tomatoes by increasing the endogenous content of indole-3-acetic acid (auxin), trans-zeatin (cytokinin), and jasmonic acid. The enhanced jasmonic acid content may have contributed to an increased production of tocochromanols because plastochromanol-8 concentration per unit of chlorophyll was higher in Pepton-treated plants compared to controls. In conclusion, the tested Pepton application may exert a positive effect on hormonal balance and the antioxidant system of plants under water stress in an economically important crop, such as tomato plants.
... Synthesis of low-molecularweight antioxidants such as α-tocopherol had been reported in drought-stressed plants (Munné-Bosch and Alegre, 2002). Oxidative stress and jasmonic acid activate the expression of genes responsible for the synthesis of tocopherols in plants (Sandorf and Holländer-Czytko, 2002). The α-tocopherol that inhibits the propagation of lipid peroxidation and is an efficient single oxygen quencher and scavenger may, therefore, contribute to the photoprotection of the photosynthetic apparatus during the first stages of leaf senescence, when chloroplasts are still retaining photosynthetic activity. ...
Drought is one of the major abiotic constraints contributing to low productivity in
maize. In tropical region, it causes grain yield losses of as high as 70% while
complete crop failure is also common depending on the severity of drought.
Drought diminishes crop productivity mainly by causing premature leaf
senescence. It is now possible to delay drought induced leaf senescence in order to
enhance tolerance to drought and stabilize crop yield through bioengineering. The
ipt gene codes for isopentenyltransferase (IPT) enzyme, which catalyzes the ratelimiting
step in the biosynthesis of cytokinin (CK) and enhances tolerance to
drought by increasing the foliar level of CK that delays drought-induced leaf
senescence in transgenic crops. This study was designed to genetically transform
locally adapted elite and commercial tropical maize genotypes with ipt gene to
develop drought stress tolerance through Agrobacterium tumefaciens-mediated
genetic transformation. Ten maize genotypes adapted to Ethiopian and the Eastern
and Central African (ECA) countries were evaluated for in vitro regeneration
ability using immature zygotic embryos as explants. Six genotypes (Melkassa-2,
Melkassa-6Q, [CML387/CML176]-B-B-2-3-2-B [QPM], CML395, CML442 and
CML216) were identified as the best regenerating ones having potential for
improvement through genetic transformation. Subsequently, the ipt gene was subcloned
into the pNOV2819 binary vector to take advantage of the pmi gene as
plant selectable marker and mannose as selective agent. The pNOV2819 binary
vector carrying the ipt gene was introduced into the Agrobacterium strain
EHA101 which was subsequently used to transform immature zygotic embryos
obtained from the six genotypes. Among the six genotypes studied, transgenic
plants were successfully regenerated in Melkassa-2 and CML216 with
regeneration efficiency of 87.5 and 59.6%, respectively. Transgenic plants were
analyzed using PCR, Southern blot and RT-PCR. Based on PCR results,
transformation efficiencies were found to be 97.4 and 100% for Melkassa-2 and
CML216, respectively, indicating stringency of the pmi/mannose based selection
system for maize transformation. Southern blot analysis indicated stable
integration of the transgene into the genome of CML216 with 2-3 copy numbers
in five independent events. In drought assay carried out in the glasshouse
transgenic plants expressing the ipt gene maintained higher leaf relative water
content (RWC) and total chlorophyll concentration during the drought period and
produced significantly higher grain yield, major yield components and root dry
matter compared to the non-transgenic plants. The ipt gene was observed to
improve drought tolerance in tropical maize by delaying drought induced leaf
senescence. It was concluded that the transgenic line developed can be further
tested for tolerance to drought under contained field trials. Furthermore it can be
used in breeding programs to improve drought tolerance in other commercial
tropical maize genotypes through conventional breeding.
... Tocopherol contributes a single electron from its chromonal ring to free oxidative species such as LOO − to form LOOH and is itself converted into a tocopheroxy radical that can be recycled again into α-Toc during a reaction with other antioxidants (Figs. 1, 2) such as ascorbate and glutathione (Munné-Bosch 2005). The action of α-Toc in protecting membranes from oxidation of polyunsaturated fatty acids involves many mechanisms (Sandorf and Hollander-Czytko 2002;Suárez-Jiménez et al. 2016). Reactive oxygen species (ROS) are formed as by-products during photosynthesis and other metabolic processes (Bhattacharya 2015). ...
Alpha-tocopherol (α-Toc) is a member of the vitamin E family and is lipid soluble. Its biosynthesis is by the reaction of isopentyl diphosphate and homogentisic acid in plastid membranes. The putative biochemical activities of tocopherols are linked with the formation of tocopherol quinone species, which subsequently undergo degradation and recycling within cells/tissues. α-Toc plays a key role in a variety of plant metabolic processes throughout the ontogeny of plants. It can maintain the integrity and fluidity of photosynthesizing membranes. It can also neutralize lipid peroxy radicals, consequently blocking lipid peroxidation by quenching oxidative cations. It preserves membrane integrity by retaining membranous structural components under environmental constraints such as water deficiency, high salt content, toxic metals, high/low temperatures, and radiations. α-Toc also induces cellular signalling pathways within biological membranes. Its biosynthesis varies during growth and developmental stages as well as under different environmental conditions. The current review primarily focuses on how α-Toc can regulate various metabolic processes involved in promoting plant growth and development under stress and non-stress and how it can effectively counteract the stress-induced high accumulation of reactive oxygen species (ROS). Currently, exogenous application of α-Toc has been widely reported as a potential means of promoting resistance in plants to a variety of stressful environments.
... The treatment of MeJA might be associated with upregulation of GSH metabolic genes resulting in biosynthesis of GSH under stress conditions (Dar et al. 2015). JA treatment to Arabidopsis plants caused accumulation of tocopherols owing to stimulation of tyrosine aminotransferase, which is the primary enzyme in the biosynthetic pathway of tocopherols (Sandorf and Holländer-Czytko 2002). Jasmonates might regulate the oxidative stress responses of plants. ...
Plant parasitic nematodes cause severe damage to cultivated crops globally. Management of nematode population is a major concern as chemicals used as nematicides have negative impact on the environment. Natural plant products can be safely used for the control of nematodes. Among various plant metabolites, plant hormones play an essential role in developmental and physiological processes and also assist the plants to encounter stressful conditions. Keeping this in mind, the present study was designed to evaluate the effect of jasmonic acid (JA) on the growth, pigments, polyphenols, antioxidants, osmolytes, and organic acids under nematode infection in tomato seedlings. It was observed that nematode inoculation reduced the growth of seedlings. Treatment with JA improved root growth (32.79%), total chlorophylls (71.51%), xanthophylls (94.63%), anthocyanins (37.5%), and flavonoids content (21.11%) when compared to inoculated seedlings alone. The JA application enhanced the total antioxidant capacity (lipid- and water-soluble antioxidants) by 38.23 and 34.37%, respectively, in comparison to infected seedlings. Confocal studies revealed that there was higher accumulation of glutathione in hormone-treated seedlings under nematode infection. Treatment with JA increased total polyphenols content (74.56%) in comparison to nematode-infested seedlings. JA-treated seedlings also enhanced osmolyte and organic acid contents under nematode stress. Overall, treatment with JA improved growth, enhanced pigment levels, modulated antioxidant content, and enhanced osmolyte and organic acid content in nematode-infected seedlings.
... Els jasmonats estan involucrats en la regulació de la tirosina aminotransferasa (TAT), que catalitza la síntesi d'hidroxifenilpiruvat (Sandorf & Holländer-Czytko, 2002 Com amb altres compostos antioxidants rellevants a la dieta humana, l'estudi dels efectes beneficiosos de la vitamina E en envelliment i malalties degeneratives cròniques presenta resultats inconsistents (Stocker & Keaney, 2004;Stocker, 2007 Brassica (Schranz et al., 2006;Town et al., 2006). Però a la vegada útil per traslladar el coneixement mecanístic generat en Arabidopsis a plantes de gran interès agronòmic i explotar l'estudi de la varietat fenotípica (Paterson et al., 2001). ...
Full text: http://hdl.handle.net/10803/404784
Food waste and loss represents 45% of fruits and vegetables production. Global change and the forecasted increase in the frequency of extreme weather events will further strain the production and the logistic chain from the field to the consumer, especially in the developing world where the cold chain cannot always be properly maintained. Post-harvest senescence and associated stresses limit longevity, but also the organoleptic quality and nutritional value of fresh products. Improved understanding of these processes creates options for better management and to inform breeding programs. After harvest, controlled exposure to abiotic stresses and/or exogenous phytohormones can enhance nutraceutical, organoleptic and commercial longevity traits. In this Thesis new methodologies to combine physiological features, hormonal and biochemical profiles, and transcriptomic tools have been developed to better characterise organ senescence processes. Thus, allowing the design of biotechnological strategies to improve the quality and/or longevity of fresh products, describing the underlying effects of this manipulation on post-harvest physiology and fruit maturation. The results suggest the potential to manipulate ABA signalling through ABA and/or pyrabactin applications to improve the post-harvest quality of green leafy vegetables (Brassica oleracea var capitata) stored at room temperature (Chapter 3) and to improve vitamin C and E content of raspberry fruits (Rubus idaeus; Chapters 1 and 2); and the characterization of the post-harvest senescence of ethylene-insensitive flowers (Lilium, Iris) and the potential of melatonin applications to improve Lilium post-harvest longevity (Chapter 1, Appendix 1). It was observed how the processes of leaf and flower senescence, and of fruit ripening, share physiological characteristics and its hormonal and redox regulation, resulting in ABA being an important regulator of these processes.
... The two reactions are mutually inverse and are analogous to the formation of L-Phe and L-Tyr in bacteria, demonstrating the existence of a second, direct, extraplastidic route to L-Phe and L-Tyr biosynthesis in plants and leading to a proposed role for PhPPY-AT and Ab-ArAT4 in modulating aromatic amino acid homeostasis 45,50 . Arabidopsis TAT genes (At2g24850, At5g53970) were both shown to encode the enzyme capable of interconverting L-Tyr and 4-HPP, as well as L-Phe and phenylpyruvate, catalysing the first step in tocopherol biosynthesis 45,64 . Another Arabidopsis TAT gene (At5g36160) was also reported to be capable of interconverting L-Tyr and 4-HPP, as well as L-Phe and phenylpyruvate 46 . ...
Rosmarinic acid (RA) and its derivants are medicinal compounds that comprise the active components of several therapeutics. We isolated and characterised a tyrosine aminotransferase of Prunella vulgaris (PvTAT). Deduced PvTAT was markedly homologous to other known/putative plant TATs. Cytoplasmic localisation of PvTAT was observed in tobacco protoplasts. Recombinantly expressed and purified PvTAT had substrates preference for L-tyrosine and phenylpyruvate, with apparent Km of 0.40 and 0.48 mM, and favoured the conversion of tyrosine to 4-hydroxyphenylpyruvate. In vivo activity was confirmed by functional restoration of the Escherichia coli tyrosine auxotrophic mutant DL39. Agrobacterium rhizogenes-mediated antisense/sense expression of PvTAT in hairy roots was used to evaluate the contribution of PvTAT to RA synthesis. PvTAT were reduced by 46–95% and RA were decreased by 36–91% with low catalytic activity in antisense transgenic hairy root lines; furthermore, PvTAT were increased 0.77–2.6-fold with increased 1.3–1.8-fold RA and strong catalytic activity in sense transgenic hairy root lines compared with wild-type counterparts. The comprehensive physiological and catalytic evidence fills in the gap in RA-producing plants which didn’t provide evidence for TAT expression and catalytic activities in vitro and in vivo. That also highlights RA biosynthesis pathway in P. vulgaris and provides useful information to engineer natural products.
... converts tyrosine to 4-hydroxyphenylpyruvate, which is in turn the substrate for several metabolic pathways leading to the synthesis of plastoquinone, rosmarinic acid, benzylisoquinoline alkaloids, and tocopherols (Lee and Facchini 2011;Riewe et al., 2012). In Arabidopsis it is upregulated by jasmonates (Sandorf et al., 2002) as well as other stress-inducing conditions (Holländer-Czytko et al., 2005). In Amaranthus caudatus and C. quinoa cell cultures, tocopherol content and TAT activity were likewise stimulated by methyl jasmonate (Antognoni et al., 2009). ...
... Recently,Zhang et al. (2014)reported that MJ treatment significantly induced the transcriptional activity of TAT gene in hairy roots of Salvia miltiorrhiza . Earlier, a similar phenomenon was observed for TAT in a jasmonate-deficient mutant of Arabidopsis thaliana (Sandorf & Holländer-Czytko, 2002). The results obtained in our study suggest that the biosynthesis of PAA and PE in buckwheat tissues likely proceeds through phenylpyruvate, which can be obtained by the action of AAT. ...
... NS, not significant. enzyme in α-tocopherol biosynthesis [34]. It is therefore likely that NPK fertilization exerts a positive role on amino acid metabolism, being drought-stressed plants more able to divert part of the amino acids to vitamin E biosynthesis. ...
... Figure 28.6 depicts the putative situation in a leaf consuming/dissipating most of the absorbed light via the combination of photochemistry and thermal dissipation (NPQ), but also forming ROS levels sufficient to trigger production of redox signals that, in turn, fully induce synthesis of factors (i) involved in thermal dissipation (NPQ) and anti-oxidation as well as (ii) biotic defenses. It has, for example, been reported that jasmonic acid triggers de-novo synthesis of the anti-oxidant tocopherols (Sandorf and Holländer-Czytko 2002 ) and ascorbic acid (Wolucka et al. 2005 ) as well as of carotenoids (Pérez et al. 1993 ). Figure 28.7 depicts a putative situation for a leaf experiencing massive ROS formation. Continuing massive ROS formation and, e.g., leaf death (for an overview of senescence and death, see Biswal et al. 2013 ) can theoretically be prevented by a shutdown of the sources of ROS production. ...
This chapter places two key photoprotective processes in the chloroplast (thermal dissipation of excess excitation energy and removal of reactive oxygen species, ROS, by anti-oxidants) into the context of whole-leaf and whole-plant function in the environment. The emerging evidence for possible trade-offs between effects of altered thermal dissipation and/or anti-oxidation capacity on plant resistance to abiotic stresses (unfavorable physical conditions) versus biotic stresses (pests and pathogens) is summarized. We conclude that more research on this topic is urgently needed, especially for specific crop species and agriculturally relevant environments, including various combinations of multiple abiotic and biotic stresses. As an example of a key redox-signaling pathway impacted by thermal dissipation and/or anti-oxidation capacity, the formation of lipid-peroxidation-derived hormonal messengers of the oxylipin family, with critical roles in plant growth, development, and defenses, is discussed. The available evidence for specific effects of the capacities of thermal dissipation and/or anti-oxidation on sugar loading into foliar phloem conduits, sugar export from leaves, whole-plant growth rate, and plant biotic defenses is reviewed. Lastly, leaf responses to moderate versus massive ROS formation via multiple feedback loops are compared and contrasted.
... These differences in tocopherols concentration may be due to the differences between rice genotypes, different methods of extraction used in the studies and may also be due to growth conditions. The expression of genes responsible for the synthesis of tocopherols in plants can be activated by oxidative stress (Sandorf and Hollander-Czytko, 2002). A half-century ago tocotrienols were discovered, but most of their biology has been uncovered only in the last decade. ...
Tocochromanols (tocopherols and tocotrienols) unitedly known as vitamin E, are the necessary antioxidant components of both human and animal diets. There is a considerable interest in plants with increased or customized vitamin E content, due to their potential health benefits. To quantify the tocochromanol content and determine the expression of a key tocotrienol biosynthesis gene among a set of contrasting red pericarp and light brown rice genotypes of advanced breeding lines together with their parents; expression pattern of homogentisate geranylgeranyl transferase (HGGT), the key gene was studied by semi-quantitative RT-PCR in milky and matured grain stages. Vitamin E analysis was carried out by high performance liquid chromatography (HPLC). The chloroform-methanolic extracts prepared from red pericarp and light brown rice advanced breeding lines showed significant differences for vitamin E content. Averaged across all samples, the content of γ-tocotrienol > α-tocopherol > α-tocotrienol > γ-tocopherol > δ-tocotrienol, and total E vitamin content ranged from 10.30 to 31.65 μg/g. Genotype G37 (red pericarp) was found to have higher expression than G7 (light brown) and G33 (red pericarp) at both grain development stages but lower than both parents whereas their transcript levels were comparatively lower in mature grain, which indicates their possible regulation by plant growth stage. HPLC results of γ-tocotrienol content supported gene expression results with the exception of the recurrent parent MR219.
... Interestingly, there are recent evidences that tocopherols might influence stress signalling by regulating jasmonic acid levels in plants (Munne-Bosch et al., 2007). In addition, Arabidopsis tyrosin aminotransferase (enzyme that precedes HPPD in the pathway) and barley hppd are positively regulated by jasmonic acid (Falk et al., 2002;Sandorf and Hollander-Czytko, 2002). ...
... Recently, Zhang et al. (2014) reported that MJ treatment significantly induced the transcriptional activity of TAT gene in hairy roots of Salvia miltiorrhiza. Earlier, a similar phenomenon was observed for TAT in a jasmonate-deficient mutant of Arabidopsis thaliana (Sandorf & Holländer-Czytko, 2002). ...
Methyl jasmonate has a strong effect on secondary metabolizm in plants, by stimulating the biosynthesis a number of phenolic compounds and alkaloids. Common buckwheat (Fagopyrum esculentum Moench) is an important source of biologically active compounds. This research focuses on the detection and quantification of 2-phenylethylamine and its possible metabolites in the cotyledons, hypocotyl and roots of common buckwheat seedlings treated with methyl jasmonate. In cotyledons of buckwheat sprouts, only traces of 2-phenylethylamine were found, while in the hypocotyl and roots its concentration was about 150 and 1000-times higher, respectively. Treatment with methyl jasmonate resulted in a 4-fold increase of the 2-phenylethylamine level in the cotyledons of 7-day buckwheat seedlings, and an 11-fold and 5-fold increase in hypocotyl and roots, respectively. Methyl jasmonate treatment led also to about 4-fold increase of phenylacetic acid content in all examined seedling organs, but did not affect the 2-phenylethanol level in cotyledons, and slightly enhanced in hypocotyl and roots. It has been suggested that 2-phenylethylamine is a substrate for the biosynthesis of phenylacetic acid and 2-phenylethanol, as well as cinnamoyl 2-phenethylamide. In organs of buckwheat seedling treated with methyl jasmonate, higher amounts of aromatic amino acid transaminase mRNA were found. The enzyme can be involved in the synthesis of phenylpyruvic acid, but the presence of this compound could not be confirmed in any of the examined organs of common buckwheat seedling.
... In the present study, OPDA levels decreased during the dry season, while JA and JA-Ile levels remained unaltered. JA, but not OPDA, has been shown to induce tyrosine aminotransferase activity, thereby increasing biosynthesis of tocopherols ( Sandorf and Holländer-Czytko 2002). Our results provide correlative evidence that ABA, rather than jasmonates, induces vitamin Tree Physiology Online at http://www.treephys.oxfordjournals.org ...
The physiological response of plants growing in their natural habitat is strongly determined by seasonal variations in environmental conditions and the interaction of abiotic and biotic stresses. Here, leaf water and nutrient contents, changes in cellular redox state and endogenous levels of stress-related phytohormones (abscisic acid (ABA), salicylic acid and jasmonates) were examined during the rainy and dry season in Vellozia gigantea, an endemic species growing at high elevations in the rupestrian fields of the Espinhaço Range in Brazil. Enhanced stomatal closure and increased ABA levels during the dry season were associated with an efficient control of leaf water content. Moreover, reductions in 12-oxo-phytodienoic acid (OPDA) levels during the dry season were observed, while levels of other jasmonates, such as jasmonic acid and jasmonoyl-isoleucine, were not affected. Changes in ABA and OPDA levels correlated with endogenous concentrations of iron and silicon, hydrogen peroxide, and vitamin E, thus indicating complex interactions between water and nutrient contents, changes in cellular redox state and endogenous hormone concentrations. Results also suggested crosstalk between activation of mechanisms for drought stress tolerance (as mediated by ABA) and biotic stress resistance (mediated by jasmonates), in which vitamin E levels may serve as a control point. It is concluded that, aside from a tight ABA-associated regulation of stomatal closure during the dry season, crosstalk between activation of abiotic and biotic defences, and nutrient accumulation in leaves may be important modulators of plant stress responses in plants growing in their natural habitat.
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... . In the " Regulation of plant immune response " category we emphasize the gene REF/SRPP-like protein At1g67360 (Taki et al. 2005), induced by a precursor of JA. C. sativa also invests in genes related to " Stress recovery " (e.g., Aminophospholipid flippase 9) (López- Marqués et al. 2012) and " HR recovery " (e.g., 4- hydroxyphenylpyruvate dioxygenase) (Sandorf and Hollander-Czytko 2002). Genes involved in " Anti-fungal Fig. 3 Differentially expressed genes in the root transcriptomes of Castanea crenata (Cc, resistant) and Castanea sativa (Cs, susceptible), P value<1E−3. ...
The European chestnut, an important forest species for the economy of Southern
Europe, covers an area of 2,53 million hectares, including 75,000 hectares devoted to
fruit production. Castanea sativa is declining due to ink disease caused by
Phytophthora cinnamomi. To elucidate chestnut defense mechanisms to ink disease
we compared the root transcriptome of the susceptible species C. sativa and the
resistant species C. crenata after P. cinnamomi inoculation. Four cDNA libraries were
constructed, two of them included root samples from C. sativa, inoculated and noninoculated
and the other two libraries comprised samples from C. crenata at identical
conditions.
Pyrosequencing produced 771,030 reads and assembly set up 15,683 contigs for C.
sativa and 16,828 for C. crenata. GO annotation revealed terms related to stress as
"response to stimulus", "transcription factor activity" or "signaling" for both
transcriptomes. Differential gene expression analysis revealed that C. crenata involved
more genes related with biotic stress upon pathogen inoculation than C. sativa. Those
genes for both species are involved in regulation of plant immune response and stress
adaptation and recovery. Furthermore, it is suggested that both species recognize the
pathogen attack; however, the resistant species may involve more genes in the
defense response than the susceptible species. RNA-seq enabled the selection of
candidate genes for ink disease resistance in Castanea. The present data is a valuable
contribution to the available Castanea genomic resources and constitutes the basis for
further studies.
... Sandorf and Hollander-Czytko [27] reported that jasmonic acid (JA) played an important role in the induction of TAT and the biosynthesis of tocopherols upon environmental stress. Previously, semi quantitative real time-PCR (qRT-PCR) analysis in S. miltiorrhiza revealed that the constitutive expression of SmTAT in the stems was much higher than that in the root and leaf [23]. ...
Rosmarinic acid (α-O-caffeoyl-3,4-dihydroxyphenylacetic acid, RA) is a caffeoyl ester widely distributed in plants. cDNA clones encoding tyrosine
aminotransferase (TAT1 and 2) and hydroxyphenylpyruvate reductase (HPPR) have been isolated from Scutellaria baicalensis. The open reading frames
(ORFs) of SbTAT1 and 2 were 1230 and 1272 bp long and encoded 409 and 423 amino acid residues, respectively. HPPR corresponded to a 942-bp ORF and
313 amino acid residues of translated protein. To study the molecular mechanisms of TAT and HPPR and investigate RA accumulation in S. baicalensis, we
examined the transcript levels of TAT isoforms and HPPR with quantitative real-time PCR and analyzed the RA content in different organs by using highperformance
liquid chromatography. The transcript levels of SbTAT1 SbTAT2, and SbHPPR in the flowers were higher than those in other organs. RA was also
highly accumulated in the flowers and with a trace amount in the roots. No RA was detected in the leaves and stems of S. baicalensis. The amount of
accumulated RA in the flowers was 28.7 times higher than that in the roots. Our results will be helpful in elucidating the mechanisms of RA biosynthesis in S.
baicalensis.
Plant species distribution across ecosystems is influenced by multiple environmental factors, and recurrent seasonal stress events can act as natural selection agents for specific plant traits and limit species distribution. For that, studies aiming at understanding how environmental constraints affect adaptive mechanisms of taxonomically closely related species are of great interest. We chose two Scabiosa species inhabiting contrasting environments: the coastal scabious S. atropurpurea, typically coping with hot‐dry summers in a Mediterranean climate, and the mountain scabious S. columbaria facing cold winters in an oceanic climate. A set of functional traits was examined to assess plant performance in these congeneric species from contrasting natural habitats. Both S. atropurpurea and S. columbaria appeared to be perfectly adapted to their environment in terms of adjustments in stomatal closure, CO 2 assimilation rate and water use efficiency over the seasons. However, an unexpected dry period during winter followed by the typical Mediterranean hot‐dry summer forced S. atropurpurea plants to deploy a set of photoprotective responses during summer. Aside from reductions in leaf water content and F v /F m , photoprotective molecules (carotenoids, α‐tocopherol and anthocyanins) per unit of chlorophyll increased, mostly as a consequence of a severe chlorophyll loss. The profiling of stress‐related hormones (ABA, salicylic acid and jasmonates) revealed associations between ABA and the bioactive jasmonoyl‐isoleucine with the underlying photoprotective response to recurrent seasonal stress in S. atropurpurea . We conclude that jasmonates may be used together with ABA as a functional trait that may, at least in part, help understand plant responses to recurrent seasonal stress in the current frame of global climate change.
Activation of hormonal responses defines the drought acclimation ability of plants and may condition their survival. However, aside ABA, little is known about the possible contribution of other phytohormones, such as jasmonates and salicylates, in the response of CAM plants to water deficit. Here, we aimed to study the physiological mechanisms underlying the stress tolerance of house leek (Sempervivum tectorum L.), a CAM plant adapted to survive harsh environments, to a combination of water deficit and nutrient deprivation. We exposed plants to the combination of these two abiotic stresses by withholding nutrient solution for 10 weeks and monitored their physiological response every two weeks by measuring various stress makers together with the accumulation of stress-related phytohormones and photoprotective molecules, such as tocopherols (vitamin E). Results showed that ABA content increased by 4.2-fold after four weeks of water deficit to keep later constant up to 10 weeks of stress, variations that occurred concomitantly with reductions in the relative leaf water content, which decreased by up to 20% only. The bioactive jasmonate, jasmonoyl-isoleucine was the other stress-related phytohormone that simultaneously increased under stress together with ABA. While contents of salicylic acid and the jasmonoyl-isoleucine precursors, 12-oxo-phytodienoic acid and jasmonic acid decreased with water deficit, those of jasmonoyl-isoleucine increased 3.6-fold at four weeks of stress. The contents of ABA and jasmonoyl-isoleucine correlated positively between them and with the content of -tocopherol per unit of chlorophyll, thus suggesting a photoprotective activation role. It is concluded that S. tectorum not only withstands a combination of water deficit and nutrient deprivation for 10 weeks without any symptom of damage but also activates effective defense strategies through the simultaneous accumulation of ABA and the bioactive jasmonate form, jasmonoyl-isoleucine.
Pistachio is a nut crop domesticated in the Fertile crescent and a dioecious species with ZW sex chromosomes. We sequenced the genomes of P. vera cultivar (cv.) Siirt, the female parent, and P. vera cv. Bagyolu, the male parent. Two chromosome-level reference genomes of pistachio were generated, and Z and W chromosomes were assembled. The ZW chromosomes originated from an autosome following the first inversion that occurred approximately 8.18 Mya. Three inversion events in the W chromosome led to the formation of a 12.7 Mb (22.8% of W chromosome) non-recombining region. These W-specific sequences contain several genes of interest that might have played a pivotal role in sex determination and contributed to the initiation and evolution of a ZW sex chromosome system in pistachio. The W-specific genes including defA, defA-like, DYT1, two PTEN1 and two tandem duplications of six VPS13A paralogs are strong candidates for sex determination or differentiation. Demographic history analysis of re-sequenced genomes support that cultivated pistachio underwent severe domestication bottlenecks at approximately 7,640 years ago, dating the domestication event close to the archeological record of pistachio domestication in Iran. We identified 390, 211, and 290 potential selective sweeps in three subgroups that underlying agronomic traits such as nut development and quality, grafting success, flowering time shift, and drought tolerance. These findings have improved our understanding of genomic basis of sex-determination/differentiation and horticulturally important traits and will accelerate the improvement of pistachio cultivars and rootstocks.
Tocopherols are an essential dietary nutrient for mammals and photosynthetic products produced by green plants. Tocopherols commonly referred to as vitamin E exist in four forms (α-, β-, γ-, and δ-tocopherol). Synthetic α-tocopherol is a mixture of eight racemic forms and is less effective than natural tocopherol, thus the demand for plant-derived tocopherols is high. Tocopherols are lipophilic antioxidant and extensively used as therapeutic agents such as anti-inflammatory, anti-infection, anticancer, immune-stimulant, and nephro-protectant. They are also used as food additives and nutraceuticals. Plant cell and tissue culture is one of the promising techniques for mass production of tocopherols to meet the commercial demand. Optimizing physical and chemical factors for in vitro culture system has resulted in better accumulation of the product. Moreover, using bioreactors, precursor feeding, elicitation, biotransformation, and metabolic engineering approaches have resulted in enhanced yield of tocopherols from in vitro cultures. The present chapter deals with various important aspects of tocopherol in vitro production such as biosynthesis of tocopherol with special emphasis on key enzymes involved in the pathway whose modulation in expression can increase the yield of the product. Topics discussed include production of tocopherol from callus, cell and organ culture, metabolic engineering for mass production, different methods employed for extraction and quantification of tocopherols, and their biological activities and commercial applications.KeywordsTocopherolPlant cell and organ cultureElicitation strategiesMetabolic engineeringBiological activityBiosynthesis
Main conclusion
Tyrosine aminotransferase (AaTAT) from the hornwort Anthoceros agrestis Paton (Anthocerotaceae) was amplified and expressed in E. coli . The active enzyme is able to accept a wide range of substrates with distinct preference for l -tyrosine, therefore, possibly catalysing the initial step in rosmarinic acid biosynthesis.
Abstract
The presence of rosmarinic acid (RA) in the hornwort A. agrestis is well known, and some attempts have been made to clarify the biosynthesis of this caffeic acid ester in lower plants. Parallel to the biosynthesis in vascular plants, the involvement of tyrosine aminotransferase (EC 2.6.1.5; TAT) as the initial step was assumed. The amplification of a nucleotide sequence putatively encoding AaTAT (Genbank MN922307) and expression in E. coli were successful. The enzyme proved to have a high acceptance of l -tyrosine ( K m 0.53 mM) whilst slightly preferring 2-oxoglutarate over phenylpyruvate as co-substrate. Applying l -phenylalanine as a potential amino donor or using oxaloacetate or pyruvate as a replacement for 2-oxoglutarate as amino acceptor resulted in significantly lower catalytic efficiencies in each of these cases. To facilitate further substrate search, two methods were introduced, one using ninhydrin after thin-layer chromatography and the other using derivatisation with o -phthalaldehyde followed by HPLC or LC–MS analysis. Both methods proved to be well applicable and helped to confirm the acceptance of further aromatic and aliphatic amino acids. This work presents the first description of a heterologously expressed TAT from a hornwort ( A. agrestis ) and describes the possible entry into the biosynthesis of RA and other specialised compounds in a so far neglected representative of terrestrial plants and upcoming new model organism.
In natural conditions, there exist different biotic and abiotic stresses. Among them, pathogens, extreme temperature, water submergence, salinity, drought, severe cold, toxic heavy metals, strong light, UV radiations, etc., cause detrimental effects on plant bodies. Reactive oxygen species (ROS) is generated as outcome of these stresses, which is found mostly in cell organelles such as chloroplast, peroxisome, mitochondria, endoplasmic reticulum, etc. ROS causes damage of plant cells by oxidizing protein, lipid, chlorophyll, and nucleic acids. Plants evolved inherent self‐combating defense strategies to resist these ROS‐induced damages. In plant bodies, enzymatic antioxidation system and nonenzymatic antioxidants confer plant's protective mechanism to combat the deleterious effects of ROS. Ascorbic acid and tocopherol are two major nonenzymatic antioxidants. These two antioxidants have capability to overcome the negative effects of free radicals and ROS. Under elevated ROS, these two nonenzymatic antioxidants can affect in genetic level by altering acclimatization process of plants. Both of ascorbate and tocopherol have metal ion chelation activity inhibiting formation of ROS. These nonenzymatic antioxidants are upregulated under induction of various stresses. The detoxification of H2O2 is done by ascorbate as substrate ascorbate peroxidase (APX). Here, ascorbate acts as electron donor. The ROS‐scavenging mechanism is performed by ascorbate–glutathione (GSH) cycle. This cycle was first observed in chloroplast and it is also called as Foyer–Halliwell–Asada cycle. Later, this cycle was found in cytosol, peroxisome, and in mitochondria. Vitamin E has two components: tocopherol and tocotrienol. The prenyl tail is associated with membrane lipid. Tocopherol has α, β, γ, and δ isoforms. Its site of synthesis is plastidial envelop stored in plastoglobuli of stroma. The antioxidant tocopherol quenches singlet oxygen (¹O2) and scavenges lipid peroxy radicals. Enhanced quantity of tocopherol was noted in spinach, pea, wheat, and grasses under water‐deficit condition. The plant growth regulators that are activated during stresses regulate the activity of tocopherol in cells. Under acute stress conditions, increased ROS in chloroplasts causes irreversible damage of α‐tocopherol.
Variation in plant adaptive strategies to the diversity and variability of the environmental factors is the key to plant developmental success. Climate change phenomenon may be considered as one of the important factors of the adverse environment since it may lead to visible changes in rainfall and temperature in the global as well as regional aspects. Under the conditions of such an unfavorable environment, plants increase the production of reactive forms of oxygen which further trigger disequilibrium between their production and removal. To control the production of reactive oxygen species (ROS), higher plants possess the ROS detoxification system which includes enzymatic and non-enzymatic antioxidant components that remove ROS and protect plant cells from oxidative damage. This chapter provides main information on ROS generation, redox balance, and plant protection in the view of ecophysiological adaptations to the adverse environment with a special focus on the antioxidant defense system.
Tocopherols and tocotrienols, commonly referred to as vitamin E, are essential compounds in food and feed. Due to their lipophilic nature they protect biomembranes by preventing the propagation of lipid-peroxidation especially during oxidative stress. Since their synthesis is restricted to photosynthetic organisms, plant-derived products are the major source of natural vitamin E. In the present study the genetic basis for high vitamin E accumulation in leaves and grains of different barley (Hordeum vulgare L.) accessions was uncovered. A genome wide association study (GWAS) allowed the identification of two genes located on chromosome 7H, homogentisate phytyltransferase (HPT-7H) and homogentisate geranylgeranyltransferase (HGGT) that code for key enzymes controlling the accumulation of tocopherols in leaves and tocotrienols in grains, respectively. Transcript profiling showed a correlation between HPT-7H expression and vitamin E content in leaves. Allele sequencing allowed to decipher the allelic variation of HPT-7H and HGGT genes corresponding to high and low vitamin E contents in the respective tissues. Using the obtained sequence information molecular markers have been developed which can be used to assist smart breeding of high vitamin E barley varieties. This will facilitate the selection of genotypes more tolerant to oxidative stress and producing high-quality grains.
In the natural environment, plants are continuously exposed to a variety of abiotic stresses yielding higher concentrations of reactive oxygen species (ROS), which may cause strong oxidation of cellular structures. To cope with oxidative stress plants have evolved very efficient antioxidant machinery, among which, lipophilic tocopherols represent an important nonenzymatic component. Tocopherol exists in four isomeric forms (α-, β-, γ-, δ-) and its composition depends on plant genotypic features and tissue type. It plays a crucial role together with other antioxidants (e.g., ascorbic acid, carotenoids, glutathione) in detoxifying ROS that emerge during stress conditions. As a component of thylakoid membranes, tocopherol acts as an important scavenger of singlet oxygen and other ROS thereby preventing lipid peroxidation and maintaining stable redox status in plant cells. In addition, tocopherols may protect the embryo from ROS during germination, under both aging and stress conditions. In this chapter, the role of tocopherols in the regulation of abiotic stress responses in plants will be emphasized.
Plastochromanol-8 (PC-8) belongs to the group of tocochromanols, and together with tocopherols and carotenoids, might help protect photosystem II from photoinhibition during environmental stresses. Here, we aimed to unravel the time course evolution of PC-8 together with that of vitamin E compounds, in maize (Zea mays L.) plants exposed to reiterated drought. Measurements were performed in plants grown in a greenhouse subjected to two consecutive cycles of drought-recovery. PC-8 contents, which accounted for more than 25% of tocochromanols in maize leaves, increased progressively in response to reiterated drought stress. PC-8 contents paralleled with those of vitamin E, particularly α-tocopherol. Profiling of the stress-related phytohormones (ABA, jasmonic acid and salicylic acid) was consistent with a role of ABA in the regulation of PC-8 and vitamin E biosynthesis during drought stress. Results also suggest that PC-8 may help tocopherols prevent damage to the photosynthetic apparatus. A better knowledge of the ABA-dependent regulation of PC-8 may help us manipulate the contents of this important antioxidant in crops.
High temperature (HT) has become a global concern because it severely affects the growth and production of crops. Heat stress causes an abrupt increase in the expression of stress-associated proteins which provide tolerance by stimulating the defense response in plants. Heat-shock proteins (Hsps) and antioxidant enzymes are important in encountering heat stress in plants. The heat-shock response is characterized by repression of normal cellular protein synthesis and induction of Hsp synthesis. Under HT stress, upregulation of various enzymatic and nonenzymatic antioxidants, maintenance of cell membrane stability, production of various compatible solutes and hormonal changes occurs. Reactive oxygen species involving several pathways such as water-water cycle, Halliwell-Asada, glutathione peroxidase, Haber-Weiss and Fenton reactions helps in protecting plants against toxic radicals which otherwise could cause damage to lipophilic protein. Genetic approaches to elucidate and map genes or quantitative trait loci conferring thermotolerance will facilitate marker-assisted breeding for heat tolerance and also pave the way for characterizing genetic factors which could be useful for engineering plants with improved heat tolerance. This review discusses the protective mechanism of heat stress responses encompassing different pathways that provide tolerance during HT stress.
Legumes belong to the family Fabaceae, and form an important part of the human diet. They are also key players in maintaining soil fertility and hence are considered as ?wonderful gift? of Nature for all living beings. However, several constraints limit the productivity of legumes, including environmental stresses like salinity, drought, waterlogging, temperature extremes, toxic metals, ozone and UV radiation. These stresses result in severe damage to the plants in terms of growth, development, metabolism and yield. Most legumes are sensitive to environmental stresses depending on the plant species, extent and duration of stresses. Considering the importance of legumes and the adverse effects of environmental stresses on their growth and productivity, looking at ways to develop stress-tolerant varieties of legume crops is a vital task for plant biologists and agronomists. Due to the multigenic nature of stresss tolerance, developing such varieties is a difficult task in most cases. Over the last few decades the effects of certain phytoprotectants, such as phytohormones, amino acids and their derivatives, antioxidants and trace elements, have been studied extensively and the results reveal that these phytoprotectants could confer stress tolerance on legumes. In this chapter, we shed light on the most recent advances in using exogenous phytoprotectants against environmental stresses in legumes.
Main conclusion
Twenty-nine genes related to phenolic acid biosynthesis were identified in the
Salvia miltiorrhiza
genome. Nineteen of these are described for the first time, with ten genes experimentally correlating to phenolic acid biosynthesis.
Vast stores of secondary metabolites exist in plants, many of which possess biological activities related to human health. Phenolic acid derivatives are a class of valuable bioactive pharmaceuticals abundant in the widely used Chinese medicinal herb, Salvia miltiorrhiza. The biosynthetic pathway for phenolic acids differs in this species from that of other investigated plants. However, the molecular basis for this is unknown, with systematic analysis of the genes involved not yet performed. As the first step towards unraveling this complex biosynthetic pathway in S. miltiorrhiza, the current genome assembly was searched for putatively involved genes. Twenty-nine genes were revealed, 19 of which are described here for the first time. These include 15 genes predicted in the phenylpropanoid pathway; seven genes in the tyrosine-derived pathway; six genes encoding putative hydroxycinnamoyltransferases, and one CYP98A, namely CYP98A78. The promoter regions, gene structures and expression patterns of these genes were examined. Furthermore, conserved domains and phylogenetic relationships with homologous proteins in other species were revealed. Most of the key enzymes, including 4-coumarate: CoA ligase, 4-hydroxyphenylpyruvate reductase and hydroxycinnamoyltransferase, were found in multiple copies, each exhibiting different characteristics. Ten genes putatively involved in rosmarinic acid biosynthesis are also described. These findings provide a foundation for further analysis of this complex and diverse pathway, with potential to enhance the synthesis of water-soluble medicinal compounds in S. miltiorrhiza.
Allene oxide synthase, an enzyme of the octadecanoid pathway to jasmonates, was cloned from Arabidopsis thaliana as a full-length cDNA encoding a polypeptide of 517 amino acids with a calculated molecular mass of 58705 Da. From the sequence, an N-terminal transit peptide of 21 amino acids resembling chloroplast transit peptides was deduced. Three out of four invariant amino acid residues of cytochrome P450 heme-binding domains are conserved and properly positioned in the enzyme coding region, including the heme-accepting cysteine (Cys-470). Southern analysis indicated in A. thaliana only one allene oxide synthase gene to be present. While transcript levels were rapidly and transiently induced after wounding of the leaves, allene oxide synthase activity remained nearly constant at a low level of ca. 0.8 nkat per mg of protein. The cDNA encoding A. thaliana allene oxide synthase was highly expressed in bacteria giving rise to a polypeptide of the calculated molecular mass. The protein was enzymatically active, and verification of the reaction products by GC-MS showed that it was capable of utilizing not only 13-hydroperoxylinolenic acid (13-hydroperoxy-9(Z), 11(E), 15(Z)-octadecatrienoic acid), but also 13-hydroperoxylinoleic acid (13-hydroperoxy-9(Z), 11(E)-octadecadienoic acid) as substrate. The data suggest parallel pathways to jasmonates from linolenic acid or linoleic acid in A. thaliana.
alpha-Tocopherol (vitamin E) is a lipid-soluble antioxidant synthesized only by photosynthetic organisms. alpha-Tocopherol is an essential component of mammalian diets, and intakes in excess of the U.S. recommended daily allowance are correlated with decreased incidence of a number of degenerative human diseases. Plant oils, the main dietary source of tocopherols, typically contain alpha-tocopherol as a minor component and high levels of its biosynthetic precursor, gamma-tocopherol. A genomics-based approach was used to clone the final enzyme in alpha-tocopherol synthesis, gamma-tocopherol methyltransferase. Overexpression of gamma-tocopherol methyltransferase in Arabidopsis seeds shifted oil compositions in favor of alpha-tocopherol. Similar increases in agricultural oil crops would increase vitamin E levels in the average U.S. diet.
The lipid-soluble antioxidants alpha-tocopherol and carnosic acid were studied in field-grown rosemary (Rosmarinus officinalis L.) plants subjected to drought. During summer in the Mediterranean region, the predawn water potential decreased to -3 MPa and the relative water content to 42%, which caused a depletion of the maximum diurnal CO(2) assimilation rate by 80%. Meanwhile, the maximum efficiency of photosystem II photochemistry and the chlorophyll content of leaves remained unaltered, indicative of the absence of photooxidative damage. The concentration of alpha-tocopherol increased by 15-fold and that of carotenoids by approximately 26% in response to water stress. Enhanced formation of the highly oxidized abietane diterpenes isorosmanol (by 25%) and dimethyl isorosmanol (by 40%) was observed during the summer as result of the oxidation of carnosic acid, which decreased by 22%. The large amounts of carnosic acid, alpha-tocopherol, and carotenoids present in rosemary leaves might contribute to the prevention of oxidative damage in plants exposed to drought.
The signaling pathways that allow plants to mount defenses against chewing insects are known to be complex. To investigate the role of jasmonate in wound signaling in Arabidopsis and to test whether parallel or redundant pathways exist for insect defense, we have studied a mutant (fad3-2 fad7-2 fad8) that is deficient in the jasmonate precursor linolenic acid. Mutant plants contained negligible levels of jasmonate and showed extremely high mortality ( approximately 80%) from attack by larvae of a common saprophagous fungal gnat, Bradysia impatiens (Diptera: Sciaridae), even though neighboring wild-type plants were largely unaffected. Application of exogenous methyl jasmonate substantially protected the mutant plants and reduced mortality to approximately 12%. These experiments precisely define the role of jasmonate as being essential for the induction of biologically effective defense in this plant-insect interaction. The transcripts of three wound-responsive genes were shown not to be induced by wounding of mutant plants but the same transcripts could be induced by application of methyl jasmonate. By contrast, measurements of transcript levels for a gene encoding glutathione S-transferase demonstrated that wound induction of this gene is independent of jasmonate synthesis. These results indicate that the mutant will be a good genetic model for testing the practical effectiveness of candidate defense genes.
Plant foods contain almost all of the mineral and organic nutrients established as essential for human nutrition, as well as a number of unique organic phytochemicals that have been linked to the promotion of good health. Because the concentrations of many of these dietary constituents are often low in edible plant sources, research is under way to understand the physiological, biochemical, and molecular mechanisms that contribute to their transport, synthesis and accumulation in plants. This knowledge can be used to develop strategies with which to manipulate crop plants, and thereby improve their nutritional quality. Improvement strategies will differ between various nutrients, but generalizations can be made for mineral or organic nutrients. This review focuses on the plant nutritional physiology and biochemistry of two essential human nutrients, iron and vitamin E, to provide examples of the type of information that is needed, and the strategies that can be used, to improve the mineral or organic nutrient composition of plants.
Analyses of tocopherols in flag leaves of barley cultivated in a field revealed that both alpha-and gamma-tocopherol accumulate with the beginning of senescence. Correspondingly one of the genes expressed during barley leaf senescence is coding for a key enzyme of the biosynthetic pathway leading to tocopherols and plastoquinones. This enzyme, 4-hydroxyphenylpyruvate dioxygenase, catalyzes the formation of homogentisate from 4-hydroxyphenylpyruvate, a product of the shikimate pathway. It is hypothesized that tocopherols acting as lipophilic antioxidants play an important role in differential stabilization of plastid envelope membranes over thylakoid membranes which become degraded during senescence. A model emphasizing the important function of envelope membranes for senescence associated remobilization of thylakoid lipids is presented.
Spinach (Spinacta oleracea L. 'Meridian') plants were irradiated for 9 h d-1 for 12 d with ultra-violet-B (UV-B) radiation [13.5 kJ m-2 d-1 of biologically effective UV-B radiation (UV-B(BE)) + 350 μmol m-2 s-1 of photosynthetically active radiation (PAR)] or PAR (350 μmol m-2 s-1) to determine if incipient UV-B-induced inhibition of photosynthetic function occurred in photosystem 2 (PS2) reaction centers or in the lipid matrix of thylakoid membranes. Chlorophyll concentrations (leaf area basis) in UV-B-irradiated spinach leaves were significantly lower than in PAR plants after 4, 8 and 12 d of exposure. A significant UV-B-induced rise in initial fluorescence (Fo) at days 8 and 10 was accompanied by a decline in the photochemical efficiency (Fv/Fm) ratio, indicating a reduction in the efficiency of PS2 energy harvesting and trapping. When based upon the chlorophyll content of thylakoid membranes, UV-B radiation did not alter lipid per-oxidation but did increase α-tocopherol content compared with the PAR treatment during the first 8 of the 12 exposure days. These data suggest that incipient UV-B damage to the photochemical apparatus did not occur in PS2 reaction center complexes nor in the lipid matrix of the thylakoid membranes. Photosynthetic function was more susceptible to UV-B-induced impairment than thylakoid membrane lipids were to UV-B radiation damage.
To isolate brassinosteroid (BR) inducible genes, a subtractive cDNA-cloning strategy was applied. One of the isolated genes encodes a plant homologue to yeast old yellow enzymes (OYE) with strong sequence similarity to two cloned 12-oxo-phytodienoic acid reductases (OPR1 and OPR2) from A. thaliana and was termed 12-oxophytodienoate reductase 3 (OPR3; accession number: AJ238149). The expression of the OPR3 gene is induced by brassinosteroids, jasmonic acid (JA), and by a variety of stimuli like UV-light, touch, wind, wounding, and application of a detergent. Recombinant OPR3 protein converts 12-oxophytodienoate (OPDA) into 12-oxo phytoenoic acid (OPC8: 0), indicating the participation of OPR3 in the biosynthesis of JA from linolenic acid via the Vick-Zimmerman-pathway. In plants, OPC8: 0 is inevitably metabolized to JA by three cycles of β-oxidation. Both OPDA and JA are signal molecules involved in developmental processes and stress responses. Depending on environmental or developmental conditions, OPR potentially regulates the ratio between these two signal molecules. The yeast old yellow enzymes act on various enones and phenols including steroids, catalyzing reduction and disproportionation reactions. Thus, in addition to OPDA to OPC8: 0 conversion, OPR3 might be involved in further biosynthetic or degradative pathways in plants. As OPR3 expression is increased through treatment with brassinosteroids, it provides a potential link between brassinosteroid action and JA synthesis. BRs may thus influence the stress responses of plants through stimulation of JA synthesis.
Tocopherols and tocotrienols, which differ only in the degree of saturation of their hydrophobic prenyl side chains, are lipid-soluble molecules that have a number of functions in plants. Synthesized from homogentisic acid and isopentenyl diphosphate in the plastid envelope, tocopherols and tocotrienols are essential to maintain membrane integrity. α-Tocopherol is the major form found in green parts of plants, while tocotrienols are mostly found in seeds. These compounds are antioxidants, thus they protect the plant from oxygen toxicity. Tocopherols and tocotrienols scavenge lipid peroxy radicals, thereby preventing the propagation of lipid peroxidation in membranes, and the ensuing products tocopheroxyl and tocotrienoxyl radicals, respectively, are recycled back to tocopherols and tocotrienols by the concerted action of other antioxidants. Furthermore, tocopherols and tocotrienols protect lipids and other membrane components by physically quenching and reacting chemically with singlet oxygen. The scavenging of singlet oxygen by α-tocopherol in chloroplasts results in the formation of, among other products, α-tocopherol quinone, a known contributor to cyclic electron transport in thylakoid membranes, therefore providing photoprotection for chloroplasts. Moreover, given that α-tocopherol increases membrane rigidity, its concentration, together with that of the other membrane components, might be regulated to afford adequate fluidity for membrane function. Furthermore, α-tocopherol may affect intracellular signaling in plant cells. The effects of this compound in intracellular signaling may be either direct, by interacting with key components of the signaling cascade, or indirect, through the prevention of lipid peroxidation or the scavenging of singlet oxygen. In the latter case, α-tocopherol may regulate the concentration of reactive oxygen species and plant hormones, such as jasmonic acid, within the cell, which control both the growth and development of plants, and also plant response to stress.
A toxin causing chlorosis in bean and soybean leaves has been isolated from liquid cultures of Pseudomonas glycinea, and purified. It has been identified as coronatine, a toxin produced also by Pseudomonas coronafaciens var. atropurpurea.
The analysis of allene oxide synthase (AOS) mRNA levels, of AOS polypeptide levels and specific enzymatic activities, as well as the quantitative determination of the levels of the octadecanoids cis-12-oxophytodienoic acid (cis-OPDA) and JA following a number of treatments, has shown that AOS is a regulatory site in octadecanoid biosynthesis in A. thaliana. AOS activity, mRNA and polypeptide levels are increased in wounded leaves locally and systemically. The methyl esters of OPDA or JA (OPDAME, JAME) and coronatine, are strong inducers of AOS mRNA, polypeptide and enzymatic activity. Ethephon also induces AOS activity. Salicylic acid (SA) was an inducer of AOS activity while abscisic acid (ABA) had no effect. At the level of the octadecanoids, the consequences of induction of AOS by the different inducers were distinctly different, depending on the nature of the inducer. Wounding led to a strong, bi-phasic accumulation of JA in wounded leaves and to a less pronounced increase in JA-levels in systemic leaves. Levels of OPDA changed very little in wounded leaves and remained constant or even declined in systemic leaves. Ethephon treatment resulted in a strong, transient increase in JA-levels kinetically coinciding with the second, more pronounced peak in wound-induced JA. In SA-treated leaves, the level of cis-OPDA increased throughout the experimental period while there was no effect on JA levels during the first 24 h following treatment and only a slight accumulation after 48 h. Clearly, mechanisms in addition to regulating substrate (LA) availability and the regulation of AOS accumulation control the output of the octadecanoid pathway.
Diphenylether-type herbicides are extremely potent inhibitors of protoporphyrinogen oxidase, a membrane-bound enzyme involved in the heme and chlorophyll biosynthesis pathways. Tritiated acifluorfen and a diazoketone derivative of tritiated acifluorfen were specifically bound to a single class of high-affinity binding sites on yeast mitochondrial membranes with apparent dissociation constants of 7 nM and 12.5 nM, respectively. The maximum density of specific binding sites, determined by Scatchard analysis, was 3 pmol.mg-1 protein. Protoporphyrinogen oxidase specific activity was estimated to be 2500 nmol protoporphyrinogen oxidized h-1.mol-1 enzyme. The diazoketone derivative of tritiated acifluorfen was used to specifically photolabel yeast protoporphyrinogen oxidase. The specifically labeled polypeptide in wild-type mitochondrial membranes had an apparent molecular mass of 55 kDa, identical to the molecular mass of the purified enzyme. This photolabeled polypeptide was not detected in a protoporphyrinogen-oxidase-deficient yeast strain, but the membranes contained an equivalent amount of inactive immunoreactive protoporphyrinogen oxidase protein.
The sparing/recycling effect of a highly purified, high molecular weight fraction of catechin oligomers (procyanidins) from Vitis vinifera seeds on alpha-tocopherol was studied in both homogeneous solution and in heterogeneous phase (phosphatidylcholine liposomes and red blood cells). By HPLC and electron spin resonance (ESR) spectroscopy we evidenced that tocopheroxyl radical, induced by reaction of alpha-tocopherol with the stable radical DPPH (2,2-diphenyl-1-picrylhydrazyl) is recycled by procyanidins. In addition procyanidins significantly and dose-dependently spare vitamin E from consumption (HPLC monitoring) during the autooxidation phase of the HO-induced peroxidation of phosphatidylcholine, by 23% at the lowest concentration (0.5 microM) and by 65.5% at 3 microM. In this membrane model the combination of 0.5 microM procyanidins and 2 microM alpha-tocopherol results in a marked delay in the appearance of conjugated dienes in respect to the single antioxidants (synergistic interaction), while catechin showed to be active only at 5 microM. In red blood cells oxidatively stressed by UVB exposure, procyanidins at 0.1-1.0 microM prevent vitamin E loss, markedly decrease membrane lipid peroxidation, linearly related to the concentration of vitamin E in the membranes, and significantly delay the onset of hemolysis (catechin protects between 5 and 10 microM).
In plants, the phytotoxin coronatine, which is an analog of the octadecanoids 12-oxo-phytodienoic acid and/or jasmonic acid, gives rise to a number of physiological responses similar to those of octadecanoids. To further elucidate the physiological role of these compounds, the differential RNA display technique was used to isolate a number of novel octadecanoid-inducible genes expressed in coronatine-treated Arabidopsis. Among these, a cDNA clone was identified that was similar to known tyrosine aminotransferases (TATs). The function was verified with the expressed recombinant protein. In Arabidopsis, the protein is present as a multimer of 98 kD, with a monomer of an apparent molecular mass of 47 kD. TAT mRNA could be induced within 2 h by various octadecanoids and by wounding of the plants. Accumulation of the TAT protein and a 5- to 7-fold increase in its enzymatic activity was observed 7 to 9 h after application of octadecanoids, coronatine, or wounding. The potential role of TAT in the defense response to herbivores and pathogens is discussed.
The enzyme geranylgeranyl reductase (CHL P) catalyses the reduction of geranylgeranyl diphosphate to phytyl diphosphate in higher-plant chloroplasts and provides phytol for both chlorophyll (Chl) and tocopherol synthesis. The reduction in CHL P activity in transgenic tobacco (Nicotiana tabacum L.) plants is accompanied by the reduction in total Chl and tocopherol content and the accumulation of geranylgeranylated Chl (ChlGG). The photosynthetic performance and the susceptibility to photo-oxidative stress have been investigated in these transgenic plants. The reduced total Chl content in Chl P antisense plants resulted in the reduction of electron transport chains per leaf area without a concomitant effect on the stoichiometry, composition and activity of both photosystems. However, Chl P antisense plants were much more sensitive to light stress. Analyses of Chl fluorescence quenching indicated an increased photoinhibitory quenching at the expense of the pH-dependent fluorescence quenching after short illumination (15 min) at moderate light intensities. Prolonged illumination (up to 1 h) at saturating light intensities induced an increased photoinactivation from which the Chl P antisense plants could not recover or could only partially recover during a subsequent low light phase. Our data imply that the presence of ChlGG has no influence on harvesting and transfer of light energy in either photosystem. However, the reduced tocopherol content of the thylakoid membrane is a limiting factor for defensive reactions to photo-oxidative stress.
The Arabidopsis opr3 mutant is defective in the isoform of 12-oxo-phytodienoate (OPDA) reductase required for jasmonic acid (JA) biosynthesis. Oxylipin signatures of wounded opr3 leaves revealed the absence of detectable 3R,7S-JA as well as altered levels of its cyclopentenone precursors OPDA and dinor OPDA. In contrast to JA-insensitive coi1 plants and to the fad3 fad7 fad8 mutant lacking the fatty acid precursors of JA synthesis, opr3 plants exhibited strong resistance to the dipteran Bradysia impatiens and the fungus Alternaria brassicicola. Analysis of transcript profiles in opr3 showed the wound induction of genes previously known to be JA-dependent, suggesting that cyclopentenones could fulfill some JA roles in vivo. Treating opr3 plants with exogenous OPDA powerfully up-regulated several genes and disclosed two distinct downstream signal pathways, one through COI1, the other via an electrophile effect of the cyclopentenones. We conclude that the jasmonate family cyclopentenone OPDA (most likely together with dinor OPDA) regulates gene expression in concert with JA to fine-tune the expression of defense genes. More generally, resistance to insect and fungal attack can be observed in the absence of JA.
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Coronatine is a toxin produced by Pseudomonas syringae pv. glycinea which induces the same chlorotic response in bean leaves as does infection by the bacterial pathogen. Although the structure of coronatine is known, the biological mode of action is not. One possible clue to its activity is the ethyl-substituted cyclopropane side chain of the molecule. This part structure (1-amino-2-ethycyclopropane-1-carboxylic acid or AEC) is an analog of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC).When coronatine was applied to bean leaf discs in solution, or to intact leaves through prick application, a substantial stimulation of ethylene production was measured. This stimulation was concomitant with an increase in ACC content of the tissue, and occurred under the same conditions as did the chlorotic response to the toxin. The stimulation of ethylene production was inhibited by aminoethoxyvinylglycine, an inhibitor of ACC synthesis. These results, along with those of experiments using l-[U-(14)C]methionine, indicated that the stimulation involved de novo production of ethylene via the methionine pathway.The whole, unhydrolyzed coronatine molecule is probably necessary to elicit both the ethylene and chlorosis responses since neither hydrolysis product (coronafacic acid and coronamic acid AEC]) is effective alone. A naturally occurring analog of coronatine, coronafacoylvaline, also stimulated ethylene production and caused chlorosis. However, the unrelated pseudomonad phytotoxin phaseolotoxin, which also causes chlorosis, did not stimulate ethylene production. Ethylene thus may have a specific role in the coronatine toxic syndrome.
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