[show abstract][hide abstract] ABSTRACT: Strigolactones, important rhizosphere signalling molecules and a class of phytohormones that control shoot architecture, are apocarotenoids of plant origin. They have a structural core consisting of a tricyclic lactone connected to a butyrolactone group via an enol ether bridge. Deuterium-labelled 5-deoxystrigol stereoisomers were administered to aquacultures of a high sorgomol-producing sorghum cultivar, Sorghum bicolor (L.) Moench, and conversion of these substrates to sorgomol stereoisomers was investigated. Liquid chromatography-mass spectrometry analyses established that 5-deoxystrigol (5-DS) and ent-2'-epi-5-deoxystrigol were absorbed by sorghum roots, converted to sorgomol and ent-2'-epi-sorgomol, respectively, and exuded out of the roots. The conversion was inhibited by uniconazole-P, implying the involvement of cytochrome P450 in the hydroxylation. These results provide experimental evidence for the postulated biogenetic scheme for formation of strigolactones, in which hydroxylation at C-9 of 5-DS can generate sorgomol.
[show abstract][hide abstract] ABSTRACT: KEY MESSAGE : Structure-activity relationship studies of strigolactones and Striga gesnerioides seed germination revealed strict structural requirements for germination induction and a new function of the plant hormones as germination inhibitors. Stereoisomers of the naturally occurring strigolactones, strigol, sorgolactone, orobanchol, sorgomol and 5-deoxystrigol, 36 in total, were prepared and screened for the ability to induce and/or inhibit the germination of Striga hermonthica and Striga gesnerioides seeds collected from mature plants that parasitized on sorghum and cowpea, respectively. All of the compounds induced S. hermonthica seed germination, albeit displayed differential activities. On the other hand, only a limited number of the compounds induced significant germination in S. gesnerioides, thus indicating strict structural requirements. Strigolactones inducing high germination in S. gesnerioides induced low germination in S. hermonthica. Strigolactones with the same configuration at C3a, C8b and C2' as that in 5-deoxystrigol (9a) induced high germination of S. hermonthica seeds, but most of them inhibited the germination of S. gesnerioides. The differential response of S. gesnerioides to strigolactones may play an important role in the survival of the species. However, the compounds could be used as means of control if mixed cropping of cowpea and sorghum is adopted.
[show abstract][hide abstract] ABSTRACT: Under a moderately heat-stressed condition, the photosystems of higher plants are damaged in the dark more easily than they are in the presence of light. To obtain a better understanding of this heat-derived damage mechanism that occurs in the dark, we focused on the involvement of the light-independent electron flow that occurs at 40 °C during the damage. In various plant species, the maximal photochemical quantum yield of photosystem (PS) II (Fv/Fm) decreased as a result of heat treatment in the dark. In the case of wheat, the most sensitive plant species tested, both Fv/Fm and oxygen evolution rapidly decreased by heat treatment at 40 °C for 30 min in the dark. In the damage, specific degradation of D1 protein was involved, as shown by immunochemical analysis of major proteins in the photosystem. Because light canceled the damage to PSII, the light-driven electron flow may play a protective role against PSII damage without light. Light-independent incorporation of reducing power from stroma was enhanced at 40 °C but not below 35 °C. Arabidopsis mutants that have a deficit of enzymes which mediate the incorporation of stromal reducing power into thylakoid membranes were tolerant against heat treatment at 40 °C in the dark, suggesting that the reduction of the plastoquinone pool may be involved in the damage. In conclusion, the enhanced introduction of reducing power from stroma into thylakoid membranes that occurs around 40 °C causes over-reduction of plastoquinone, resulting in the damage to D1 protein under heat stress without linear electron flow.
[show abstract][hide abstract] ABSTRACT: Lipid peroxide-derived reactive carbonyls (RCs) can cause serious damage to plant functions. A chloroplastic NADPH-dependent alkenal/one oxidoreductase (AOR) detoxifies RCs, but its physiological significance remains unknown. In this study, we investigated the biological impacts of AOR using an AOR-knock out Arabidopsis line (aor). Methyl viologen treatment, mainly to enhance photosystem (PS) I-originated reactive oxygen species (ROS) production, caused more severe damage to aor than wild type (Col-0). In contrast, the high light treatment used to enhance PSII-originated ROS production resulted in no difference in PSII damage between Col-0 and aor. In conclusion, AOR can contribute to detoxify stromal RCs produced under oxidative stress.
[show abstract][hide abstract] ABSTRACT: Coumarins are important compounds that contribute to the adaptation of plants to biotic or abiotic stresses. Among coumarins, umbelliferone occupies a pivotal position in the plant phenylpropanoid network. Previous studies indicated that umbelliferone is derived from the ortho-hydroxylation of p-coumaric acid by an unknown biochemical step to yield 2,4-dihydroxycinnamic acid, which then undergoes spontaneous lactonization. Based on a recent report of a gene encoding a 2-oxoglutarate-dependent dioxygenase from Arabidopsis thaliana that exhibited feruloyl CoA 6'-hydroxylase activity (Bourgaud et al., 2006), we combined a bioinformatic approach and a cDNA library screen to identify an orthologous ORF (Genbank accession number JF799117) from Ruta graveolens L. This ORF shares 59% amino acid identity with feruloyl CoA 6'-hydroxylase, was functionally expressed in Escherichia coli, and converted feruloyl CoA into scopoletin and p-coumaroyl CoA into umbelliferone with equal activity. Its bi-functionality was further confirmed in planta: transient expression of JF799117 in Nicotiana benthamiana yielded plants with leaves containing high levels of umbelliferone and scopoletin when compared to control plants, which contained barely detectable traces of these compounds. The expression of JF799117 was also tightly correlated to the amount of umbelliferone that was found in UV-elicited R. graveolens leaves. Therefore, JF799117 encodes a p-coumaroyl CoA 2'-hydroxylase in R. graveolens, which represents a previously uncharacterized step in the synthesis of umbelliferone in plants. Psoralen, which is an important furanocoumarin in R. graveolens, was found to be a competitive inhibitor of the enzyme, and it may exert this effect through negative feedback on the enzyme at an upstream position in the pathway.
The Plant Journal 12/2011; 70(3):460-70. · 6.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: Striga gesnerioides is a root parasitic weed of economic significance to cowpea (Vigna unguiculata) crops in Western Africa. Seeds of the parasite germinate in response to cowpea root exudates. Germination stimulants for the seeds were isolated from the hydroponic culture filtrate of cowpea, and their structures were unambiguously determined as (-)-(3aR,4R,8bR,2'R)-ent-2'-epi-orobanchol and (+)-(3aR,4R,8bR,2'R)-ent-2'-epi-orobanchyl acetate, on the basis of mass, CD, and (1)H NMR spectra; optical rotatory power; and chromatographic behavior on HPLC. The alcohol was first isolated and identified from the cowpea root exudates, and the acetate may be the same compound that had been previously isolated from the exudates and designated as alectrol. Identity of the stimulants produced by cowpea to those produced by red clover (Trifolium pratense) was confirmed.
Journal of Agricultural and Food Chemistry 09/2011; 59(19):10485-90. · 2.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Strigolactones are highly potent germination stimulants for seeds of the parasitic weeds Striga and Orobanche spp. 4-Hydroxy-GR24 and 4-acetoxy-GR24 were prepared and their abilities to induce seed germination of Striga gesnerioides evaluated. Optically active (8bR,2'R)-isomers induced germination, although the racemic diastereomers were inactive. In contrast, the stereoisomer of GR24 with the same configuration induced negligible germination. Some stereoisomers of GR24 and its analogues acted as effective antagonists for induction of seed germination by cowpea root exudates. These results suggest that both an oxygenated substituent at C-4 and the configuration of the tricyclic lactone and the D-ring are essential structural requirements for induction of germination in S. gesnerioides seeds.
Journal of Agricultural and Food Chemistry 08/2011; 59(17):9226-31. · 2.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Sorgomol, isolated from Sorghum bicolor, is the germination stimulant for seeds of root parasitic weeds. The first synthesis of (±)-sorgomol has been achieved by starting from ethyl 2-oxocyclohexanecarboxylate.
Tetrahedron Letters - TETRAHEDRON LETT. 01/2011; 52(6):724-726.
[show abstract][hide abstract] ABSTRACT: Reactive carbonyls, especially α,β-unsaturated carbonyls produced through lipid peroxidation, damage biomolecules such as proteins and nucleotides; elimination of these carbonyls is therefore essential for maintaining cellular homeostasis. In this study, we focused on an NADPH-dependent detoxification of reactive carbonyls in plants and explored the enzyme system involved in this detoxification process. Using acrolein (CH(2) = CHCHO) as a model α,β-unsaturated carbonyl, we purified a predominant NADPH-dependent acrolein-reducing enzyme from cucumber leaves, and we identified the enzyme as an alkenal/one oxidoreductase (AOR) catalyzing reduction of an α,β-unsaturated bond. Cloning of cDNA encoding AORs revealed that cucumber contains two distinct AORs, chloroplastic AOR and cytosolic AOR. Homologs of cucumber AORs were found among various plant species, including Arabidopsis, and we confirmed that a homolog of Arabidopsis (At1g23740) also had AOR activity. Phylogenetic analysis showed that these AORs belong to a novel class of AORs. They preferentially reduced α,β-unsaturated ketones rather than α,β-unsaturated aldehydes. Furthermore, we selected candidates of other classes of enzymes involved in NADPH-dependent reduction of carbonyls based on the bioinformatic information, and we found that an aldo-keto reductase (At2g37770) and aldehyde reductases (At1g54870 and At3g04000) were implicated in the reduction of an aldehyde group of saturated aldehydes and methylglyoxal as well as α,β-unsaturated aldehydes in chloroplasts. These results suggest that different classes of NADPH-dependent reductases cooperatively contribute to the detoxification of reactive carbonyls.
Journal of Biological Chemistry 12/2010; 286(9):6999-7009. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Previously we observed that the oxygen-evolving complex 33 kDa protein (OEC33) which stabilizes the Mn cluster in photosystem II (PSII), was modified with malondialdehyde (MDA), an end-product of peroxidized polyunsaturated fatty acids, and the modification increased in heat-stressed plants (Yamauchi et al. 2008). In this study, we examined whether the modification of OEC33 with MDA affects its binding to the PSII complex and causes inactivation of the oxygen-evolving complex. Purified OEC33 and PSII membranes that had been removed of extrinsic proteins of the oxygen-evolving complex (PSIIOEE) of spinach (Spinacia oleracea) were separately treated with MDA. The binding was diminished when both OEC33 and PSIIOEE were modified, but when only OEC33 or PSIIOEE was treated, the binding was not impaired. In the experiment using thylakoid membranes, release of OEC33 from PSII and corresponding loss of oxygen-evolving activity were observed when thylakoid membranes were treated with MDA at 40 degrees C but not at 25 degrees C. In spinach leaves treated at 40 degrees C under light, maximal efficiency of PSII photochemistry (F(v)/F(m) ratio of chlorophyll fluorescence) and oxygen-evolving activity decreased. Simultaneously, MDA contents in heat-stressed leaves increased, and OEC33 and PSII core proteins including 47 and 43 kDa chlorophyll-binding proteins were modified with MDA. In contrast, these changes were to a lesser extent at 40 degrees C in the dark. These results suggest that MDA modification of PSII proteins causes release of OEC33 from PSII and it is promoted in heat and oxidative conditions.
[show abstract][hide abstract] ABSTRACT: The root parasitic plant, Striga hermonthica, constrains the production of several agronomically important poaceous crops in the arid and semiarid tropical regions of Sub-Saharan Africa. The parasite is incompatible with the model legume, Lotus japonicus. Studies at the molecular and metabolic levels have revealed that expression of the genes involved in the biosynthesis of vestitol, a legume-specific phytoalexin, was highly up-regulated in L. japonicus roots challenged with S. hermonthica. High-performance liquid chromatography and mass spectroscopy confirmed the presence of vestitol in the exudate released from L. japonicus roots inoculated with S. hermonthica seedlings. Fluorescence, similar to that emitted by authentic vestitol, was displayed on the surface of L. japonicus roots to which successful attachment of S. hermonthica had been achieved. Vestitol exerted a limited inhibitory effect on S. hermonthica germination, but it significantly inhibited seedling growth. These results indicate that vestitol biosynthesis in L. japonicus was induced by S. hermonthica attachment and that vestitol contributed, at least in part, to the host's defence mechanism and acted as a chemical barrier against the intrusion of the parasite.
Bioscience Biotechnology and Biochemistry 01/2010; 74(8):1662-7. · 1.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Dechlorodauricumine (5) and dechloroacutumine (6) were converted to miharumine (7) and dechloroacutumidine (8), respectively, by a cell-free preparation from cultured roots of Menispermum dauricum in the presence of FAD. The structures of 7 and 8 were elucidated on the basis of spectroscopic analyses and chemical conversion.
Bioscience Biotechnology and Biochemistry 03/2009; 73(2):440-2. · 1.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Metabolites of the fungus Fusarium solani (Sud 96) inhibited Striga hermonthica germination induced by the germination stimulant GR24. The active principles were identified as trichothecenes acuminatin, neosolaniol, 8-acetylneosolaniol, and tetraacetoxy T-2 tetraol (neosolaniol diacetate) on the basis of their chromatographic behavior and nuclear magnetic resonance and mass spectra. Inhibitory activity of the four trichothecenes against Striga germination increased with acetylation of the hydroxyl moieties. The most abundant inhibitor produced by the fungus, 8-acetylneosolaniol, completely inhibited Striga germination at 24 μM. The fungal toxin did not affect the germination of sorghum, a host crop, but retarded root and shoot elongation of the seedlings by 60 and 30%, respectively, at the same concentration. Nomenclature: Fusarium solani (Mart.) Sacc.; sorghum, Sorghum bicolor (L.) Moench; Striga hermonthica (Del.) Benth.
[show abstract][hide abstract] ABSTRACT: An isolate of Fusarium solani (Sud 96) obtained from infected Striga plants in Sudan and six other isolates from Japan were evaluated for their effects on Striga germination. Among all the isolates, only the one from Sudan demonstrated high inhibitory activity. Aqueous and organic solvent culture extracts, as well as fungus suspension, when mixed with GR24, a synthetic analog of the natural germination stimulant strigol, inhibited germination of conditioned Striga seeds. Fusarium solani (Sud 96) filtrates, from cultures grown on autoclaved rice, sorghum grains, and potato dextrose agar (PDA), were more effective in reducing Striga germination than those from cultures grown on wheat straw. A significant difference between rice compared to sorghum and PDA cultures only occurred at high dilutions (40-fold). Complete inhibition of germination occurred when F. solani (Sud 96) culture filtrates and GR24 were applied simultaneously. Filtrate treatments made 2, 4 and 6 h subsequent to treatment with GR24 were less inhibitory. Filtrate treatments applied 8 h or more following GR24 had negligible effects on germination. Chromatographic separation on a silica gel column indicated the presence of several compounds with high inhibitory activity. Nomenclature: Fusarium solani (Mart.) Sacc.; rice, Oryza sativa L.; sorghum, Sorghum bicolor (L.) Moench; wheat, Triticum aestivum L.; witchweed, Striga hermonthica (Del.) Benth.
[show abstract][hide abstract] ABSTRACT: Lotus japonicus genes responsive to parasitism by the compatible species Orobanche aegyptiaca and the incompatible species Striga hermonthica were isolated by using the suppression subtractive hybridization (SSH) strategy. O. aegyptiaca and S. hermonthica parasitism specifically induced the expression of genes involved in jasmonic acid (JA) biosynthesis and phytoalexin biosynthesis, respectively. Nodulation-related genes were almost exclusively found among the Orobanche-induced genes. Temporal gene expression analyses revealed that 19 out of the 48 Orobanche-induced genes and 5 out of the 48 Striga-induced genes were up-regulated at 1 dai. Four genes, including putative trypsin protease inhibitor genes, exhibited systemic up-regulation in the host plant parasitized by O. aegyptiaca. On the other hand, S. hermonthica attachment did not induce systemic gene expression.
Journal of Experimental Botany 01/2009; 60(2):641-50. · 5.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: The structure proposed for solanacol, the germination stimulant for seeds of root parasitic weeds isolated from tobacco (Nicotiana tabacum L.), was synthesized. Comparison of the 1H NMR data of the synthetic compounds with those reported for solanacol showed the previously proposed structure to be incorrect.
Tetrahedron Letters - TETRAHEDRON LETT. 01/2009; 50(31):4549-4551.
[show abstract][hide abstract] ABSTRACT: Witchweeds (Striga spp.) and broomrapes (Orobanche spp.) are obligate root parasitic plants on economically important field and horticultural crops. The parasites' seeds are induced to germinate by root-derived chemical signals. The radicular end is transformed into a haustorium which attaches, penetrates the host root and establishes connection with the vascular system of the host. Reactions of Lotus japonicus, a model legume for functional genomics, were studied for furthering the understanding of host-parasite interactions. Lotus japonicus was compatible with Orobanche aegyptiaca, but not with Orobanche minor, Striga hermonthica and Striga gesnerioides. Orobanche minor successfully penetrated Lotus japonicus roots, but failed to establish connections with the vascular system. Haustoria in Striga hermonthica attached to the roots, but penetration and subsequent growth of the endophyte in the cortex were restricted. Striga gesnerioides did not parasitize Lotus japonicus. Among seven mutants of Lotus japonicus (castor-5, har1-5, alb1-1, ccamk-3, nup85-3, nfr1-3 and nsp2-1) with altered characteristics in relation to rhizobial nodulation and mycorrhizal colonization, castor-5 and har1-5 were parasitized by Orobanche aegyptiaca with higher frequency than the wild type. In contrast, Orobanche aegyptiaca tubercle development was delayed on the mutants nup85-3, nfr1-3 and nsp2-1. These results suggest that nodulation, mycorrhizal colonization and infection by root parasitic plants in Lotus japonicus may be modulated by similar mechanisms and that Lotus japonicus is a potential model legume for studying plant-plant parasitism.
Journal of plant physiology 09/2008; 166(4):353-62. · 2.50 Impact Factor