Methyl jasmonate is a more effective senescence-promoting factor in Cucurbita pepo (zucchini) cotyledons when compared with darkness at the early stage of senescence

Academy of Sciences of the Czech Republic, Praha, Praha, Czech Republic
Journal of Plant Physiology (Impact Factor: 2.56). 10/2007; 164(9):1179-87. DOI: 10.1016/j.jplph.2006.07.008
Source: PubMed


The effects of short-term darkening and methyl jasmonate (MeJA) on cotyledon senescence were studied 24h after transfer of intact 7-day-old Cucurbita pepo (zucchini) seedlings to darkness or spraying with 100 microM MeJA. The jasmonate inhibitory effect on chlorophyll content and chloroplast transcriptional activity was stronger compared with darkness. Further, MeJA reduced the photosynthetic rate whereas darkness did not affect photosynthesis. Neither stress factor affected the photochemical quantum efficiency of photosystem II (PSII) estimated by the variable fluorescence (F(v))/maximal fluorescence (F(m)) ratio, suggesting the existence of mechanisms protecting the functional activity of PSII at earlier stages of senescence, thus making this parameter more stable compared to others used to quantify senescence. Both stress factors caused a decrease in the content of physiologically active cytokinins, especially trans-zeatin (Z), with the jasmonate effect being much more pronounced when compared to darkness. Our results indicate that MeJA is a more potent inducer of senescence in zucchini cotyledons, at least within the relatively short period of the 24h treatment. This is likely due to its stronger down-regulatory effect on the levels of physiologically active cytokinins.

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Available from: Miroslav Kamínek
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    • "However, G. dura in the present study showed the symptoms of depigmentation and bleaching at the 100 mM MeJA dose at 48 h, possibly due to the higher levels of ROS accumulation. The degradation of Chl a has also been observed in higher plants in response to MeJA-induced oxidative stress (Ananieva et al. 2007, Gómez et al. 2010). A decrease in Chl a content was accompanied by an increase in phycobiliproteins (especially phycoerythrin), as found in Gracilaria thalli exposed to abiotic stresses (Kumar et al. 2010, Kumar et al. 2011). "
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    ABSTRACT: The role of exogenously added methyl jasmonate (MeJA), a lipid-derived signaling compound, in inducing oxidative stress in the marine red macroalga Gracilaria dura was investigated. MeJA at a concentration of 1-100 µM was a strong stimulant of reactive oxygen species (H2O2, HO· and O(2) (·-)) (P < 0.05) causing considerable oxidative stress in G. dura. This further led to lipid peroxidation and degradation of the pigments Chl a and phycocyanin, with a concomitant increase in phycoerythrin. The MeJA-induced oxidative burst also led to the induction of a fatty acid oxidation cascade, resulting in the synthesis of hydroxy-oxylipins and the up-regulation of the 13-lipoxygenase pathway. Electrospray ionization-mass spectrometry-based shotgun lipidomic analysis revealed that monogalactosyldiacylglycerol (a chloroplastic glycerolipid) and phosphatidylcholine (extrachloroplastidic phopholipid) were the most affected lipid classes. The degradation of 18:3-fatty acid-containing monogalactosyldiacylglycerol inferred that it provided fatty acyl chains for the biosynthesis of 13-hydroperoxylinolenic acid, which was further directed towards either the jasmonate pathway or other alternative pathways of the fatty acid oxidation cascade, analogous to higher plants. Also, G. dura modulated the lipid acyl chains in such a way that no significant change was observed in the fatty acid profile of the treated thalli as compared with those of the control, except for C16:0, C16:1 (n-9), C20:3 (n-6) and C20:4 (n-6) (P < 0.05). Furthermore, MeJA caused the accumulation of phenolic compounds and the up-regulation of enzymes involved in secondary metabolism such as polyphenol oxidase, shikimate dehydrogenase and phenylalanine ammonia-lyase, indicating a shift towards secondary metabolism as a defense strategy to combat the induced oxidative stress.
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    • "In addition, MeJA treatment decreased the levels of PSI type III chlorophyll a/b-binding protein (spots 29 and 30), CAB1 (chlorophyll A/B binding protein 1, spots 14, 15, 16, 17, 18), as well as three chlorophyll biosynthesis-related proteins, 4-nitrophenylphosphatase-like protein (spot 1), chlorina 42 (spots 20 and 21) and CHLM (magnesium-protoporphyrin IX methyltransferase, spot 19) (Table 1, Fig. 1). In previous studies , the expression of chlorophyll-related genes and chlorophyll content were reported to decrease after JA treatment (Benedetti et al., 1998; Ananieva et al., 2007; Jung et al., 2007; Zhai et al., 2007). These results indicate that the inhibitory effect of JAs on photosynthesis was achieved by reducing the size of the effective light-harvesting complexes and decreasing the carbon fixation process. "
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    ABSTRACT: Jasmonates (JAs) are the well characterized fatty acid-derived cyclopentanone signals involved in the plant response to biotic and abiotic stresses. JAs have been shown to regulate many aspects of plant metabolism, including glucosinolate biosynthesis. Glucosinolates are natural plant products that function in defense against herbivores and pathogens. In this study, we applied a proteomic approach to gain insight into the physiological processes, including glucosinolate metabolism, in response to methyl jasmonate (MeJA). We identified 194 differentially expressed protein spots that contained proteins that participated in a wide range of physiological processes. Functional classification analysis showed that photosynthesis and carbohydrate anabolism were repressed after MeJA treatment, while carbohydrate catabolism was up-regulated. Additionally, proteins related to the JA biosynthesis pathway, stress and defense, and secondary metabolism were up-regulated. Among the differentially expressed proteins, many were involved in oxidative tolerance. The results indicate that MeJA elicited a defense response at the proteome level through a mechanism of redirecting growth-related metabolism to defense-related metabolism.
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    • "There was, however, a weak reducing effect of BR on transcript accumulation in apical leaf segments, similar to the effects of IAA and GA 3 (Fig. 6). Ananieva et al. (2007) reported an inhibitory effect of MeJA on the total transcriptional activity of chloroplasts in cotyledons of Cucurbita pepo seedlings, a dicotyledonous plant. We confirm this observation with a study on primary leaves of a monocot plant, Hordeum vulgare (Fig. 3). "
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    ABSTRACT: Phytohormones control growth and development of plants. Their effects on the expression of nuclear genes are well investigated. Although they influence plastid-related processes, it is largely unknown whether phytohormones exert their control also by regulating the expression of plastid/chloroplast genes. We have therefore studied the effects of methyl jasmonate (MeJA), gibberellic acid (GA(3)), an auxin (indole-3-acetic acid, IAA), a brassinosteroid (24-epibrassinolide, BR) and a cytokinin (6-benzyladenine) on transcription (run-on assays) and transcript levels (RNA blot hybridization) of chloroplast genes after incubation of detached barley leaves in hormone solutions. BR was the only hormone without significant influence on chloroplast transcription. It showed, however, a weak reducing effect on transcript accumulation. MeJA, IAA and GA(3) repressed both transcription and transcript accumulation, while BA counteracted the effects of the other hormones. Effects of phytohormones on transcription differed in several cases from their influence on transcript levels suggesting that hormones may act via separate signaling pathways on transcription and transcript accumulation in chloroplasts. We observed striking differences in the response of chloroplast gene expression on phytohormones between the lower (young cells) and the upper segments (oldest cells) of barley leaves. Quantity and quality of the hormone effects on chloroplast gene expression seem to depend therefore on the age and/or developmental stage of the cells. As the individual chloroplast genes responded in different ways on phytohormone treatment, gene- and transcript-specific factors should be involved. Our data suggest that phytohormones adjust gene expression in the nucleo-cytoplasmic compartment and in plastids/chloroplasts in response to internal and external cues.
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