Identification of a functional allene oxide synthase-lipoxygenase fusion protein in the soft coral Gersemia fruticosa suggests the generality of ...

Identification of a functional allene oxide synthase-lipoxygenase fusion protein in the soft coral Gersemia fruticosa suggests the generality of this pathway in octocorals

The conversion of fatty acid hydroperoxides to allene epoxides is catalysed by a cytochrome P450 in plants. In contrast, in the coral Plexaura homomalla, a catalase-related hemoprotein fused to the lipoxygenase (LOX) was found to function as an allene oxide synthase. This work reports the homology-based RT-PCR cloning and functional expression of a Gersemia fruticosa analogue of the allene oxide synthase-lipoxygenase (AOS-LOX) fusion protein. The G. fruticosa mRNA codes for a protein with 84% sequence identity to the P. homomalla AOS-LOX. Our data indicate that the AOS-LOX fusion protein pathway is used by another coral and P. homomalla represents no exception.

Source: Biochim Biophys Acta. (2008) vol. 1780, p. 315-321

Cold and water stresses produce changes in endogenous jasmonates in two populations of Pinus pinaster Ait

There is considerable evidence suggesting that jasmonates (JAs) play a role in plant resistance against abiotic stress. It is well known that in Angiosperms JAs are involved in the defense response, however there is little information about their role in Gymnosperms. Our proposal was to study the involvement of JAs in Pinus pinaster Ait. reaction to cold and water stress, and to compare the response of two populations of different provenances (Gredos and Bajo Tiétar) to these stresses. We detected 12-oxo-phytodienoic acid (OPDA), jasmonic acid (JA), and the hydroxylates 11-hydroxyjasmonate and 12-hydroxyjasmonate in foliage and shoots of P. pinaster plants. The response of the Gredos population to cold stress differed from that of Bajo Tiétar. Gredos plants showed a lower JA-basal level than Bajo Tiétar; under cold stress JA increased twofold at 72 h, while it decreased in Bajo Tiétar plants. The hydroxylates slightly increased in both populations due to cold stress treatment. Under water stress, plants from Gredos showed a remarkable JA-increase; thus the JA-response was much more prominent under water stress than under cold stress. In contrast, no change was found in JA-level in Bajo Tiétar plants under water stress. The level of JA-precursor, OPDA, was very low in control plants from Gredos and Bajo Tiétar. Under water stress OPDA increased only in plants from Bajo Tiétar. Therefore, we inform here of a different JAs-accumulation pattern after the stress treatment in P. pinaster from two provenances, and suggest a possible correlation with adaptations to diverse ecological conditions.

Source: Plant Growth Regulation (2007) vol. 52, p.111-116

The Jasmonate-Induced Expression of the Nicotiana tabacum Leaf Lectin

Previous experiments with tobacco (Nicotiana tabacum L. cv Samsun NN) plants revealed that jasmonic acid methyl ester (JAME) induces the expression of a cytoplasmic/nuclear lectin in leaf cells and provided the first evidence that jasmonates affect the expression of carbohydrate-binding proteins in plant cells. To corroborate the induced accumulation of relatively large amounts of a cytoplasmic/nuclear lectin, a detailed study was performed on the induction of the lectin in both intact tobacco plants and excised leaves. Experiments with different stress factors demonstrated that the lectin is exclusively induced by exogeneously applied jasmonic acid and JAME, and to a lesser extent by insect herbivory. The lectin concentration depends on leaf age and the position of the tissue in the leaf. JAME acts systemically in intact plants but very locally in excised leaves. Kinetic analyses indicated that the lectin is synthesized within 12 h exposure time to JAME, reaching a maximum after 60 h. After removal of JAME, the lectin progressively disappears from the leaf tissue. The JAME-induced accumulation of an abundant nuclear/cytoplasmic lectin is discussed in view of the possible role of this lectin in the plant.

Source: Plant and cell physiology (2007) vol. 48, p. 1207-1218

Expression of an NADP-malic enzyme gene in rice (Oryza sativa. L) is induced by environmental stresses; over-expression of the gene in ...

Expression of an NADP-malic enzyme gene in rice (Oryza sativa. L) is induced by environmental stresses; over-expression of the gene in Arabidopsis confers salt and osmotic stress tolerance

NADP-malic enzyme (NADP-ME, EC 1.1.1.40) functions in many different pathways in plants, and has recently been implicated in plant defense such as in responses to wounding and UV-B radiation. In this study, we isolated a complementary DNA (cDNA) clone by using the differential display method and screening of a root cDNA library of rice (Oryza sativa. L) under carbonate (NaHCO3) stress, and identified it as one of the rice NADP-ME genes (we named it NADP-ME2, GenBank accession no. AB053295). The 5' end of NADP-ME2 was obtained by the 5'-RACE method, and the full-length cDNA had a length of 2217 bp encoding 593 amino acids. Expression of NADP-ME2 mRNA in roots was induced by stress from carbonates (NaHCO3 and Na2CO3, NaCl, and environmental pH changes. NADP-ME2 transcripts increased during 72-h exposures to NaHCO3, NaCl, and PEG stresses. Furthermore, NADP-ME activities in leaves and roots of rice seedlings increased by more than 50% in the presence of carbonates (NaHCO3 and Na2CO3), NaCl, and PEG. These results indicate that rice NADP-ME2 responds to salts and osmotic stresses. Transgenic Arabidopsis plants over-expressing NADP-ME2 were obtained through transformation, screening, Northern analysis and in situ NADP-ME activity assay. Transgenic Arabidopsis plants over-expressing NADP-ME2 grew well in 1/2 x MS medium with 100 mM NaCl or 4% mannitol, whereas growth of wild-type (WT) Arabidopsis seedlings was strongly inhibited. In addition, under 125 mM NaCl stress, the root lengths of transgenic lines were about twice as long as those of the WT. These results suggest that NADP-ME2 has a role in enhancing tolerance of plants to salt and osmotic stress.

Source: Plant Mol Biol. (2007) vol. 64, p. 49-58

Enhancing salt tolerance in a crop plant by overexpression of glyoxalase II

Earlier we have shown the role of glyoxalase overexpression in conferring salinity tolerance in transgenic tobacco. We now demonstrate the feasibility of same in a crop like rice through overproduction of glyoxalase II. The rice glyoxalase II was cloned in pCAMBIA1304 and transformed into rice (Oryza sativa cv PB1) via Agrobacterium. The transgenic plants showed higher constitutive activity of glyoxalase II that increased further upon salt stress, reflecting the upregulation of endogenous glyoxalase II. The transgenic rice showed higher tolerance to toxic concentrations of methylglyoxal (MG) and NaCl. Compared with non-transgenics, transgenic plants at the T1 generation exhibited sustained growth and more favorable ion balance under salt stress conditions.

Source: Transgenic Res. (2008) vol. 17, p. 171-180

Wounding increases salt tolerance in tomato plants: evidence on the participation of calmodulin-like activities in cross-tolerance signalling

Cross-tolerance is the phenomenon by which a plant resistance to a stress results in resistance to another form of stress. It has previously been shown that salt stress causes the accumulation of proteinase inhibitors and the activation of other wound-related genes in tomato plants (Solanum lycopersicum). However, very little is known about how different stresses interact with one another, and which are the signalling components that interrelate the responses triggered by different stress types. In the present work, it is shown that mechanical wounding increases salt-stress tolerance in tomato plants through a mechanism that involves the signalling peptide systemin and the synthesis of JA. Data are also provided indicating that calmodulin-like activities are necessary for the downstream signalling events that lead to cross-tolerance between wounding and salt stress. Finally, evidence was gathered supporting the hypothesis that LeCDPK1, a Ca2+-dependent protein kinase from tomato previously described in our laboratory, could participate in this cross-tolerance mechanism interrelating the signalling responses to wounding and salt stress.

Source: Journal of Experimental Botany (2006) vo.. 57, p. 2391-2400

Hydrogen peroxide is involved in methyl jasmonate-induced senescence of rice leaves

The role of H2O2 in the senescence of detached rice leaves induced by methyl jasmonate (MJ) was investigated. MJ treatment resulted in H2O2 production in detached rice leaves, which was prior to the occurrence of leaf senescence. Dimethylthiourea, a chemical trap of H2O2, was observed to be effective in inhibiting MJ-induced senescence and MJ-increased malondialdehyde (MDA) content in detached rice leaves. Diphenyleneiodonium chloride (DPI) and imidazole (IMD), inhibitors of NADPH oxidase, prevented MJ-induced H2O2 production, suggesting that NADPH oxidase is a H2O2-generating enzyme in MJ-treated detached rice leaves. DPI and IMD also inhibited MJ-promoted senescence and MJ-increased MDA content in detached rice leaves. Phosphatidylinositol 3-kinase inhibitors wortmannin (WM) or LY 294002 (LY) inhibited MJ-induced H2O2 production and senescence of detached rice leaves. Exogenous H2O2 reversed the inhibitory effect of WM or LY. In terms of leaf senescence, it was observed that rice seedlings of cultivar Taichung Native 1 (TN1) are jasmonic acid (JA)-sensitive and those of cultivar Tainung 67 (TNG67) are JA-insensitive. On treatment with JA, H2O2 accumulated in the leaves of TN1 seedlings but not in the leaves of TNG67. Evidence was also provided to show that MJ-induced H2O2 production in detached rice leaves is abscisic acid (ABA)-independent. Ethylene action inhibitor, silver thiosulfate, was observed to inhibit MJ- and ABA-induced H2O2 production and senescence of detached rice leaves, suggesting that the action of MJ and ABA is ethylene-dependent.

Source: Physiologia Plantarum (2006) vol. 127, p. 293-303