A reassessment of the prevalent organic solutes constitutively accumulated and potentially involved in osmotic adjustment in pear leaves

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceIn higher plants, osmotic adjustment at the various levels of plant organization is partly achieved through accumulation of a range of osmolytes especially LMW organic solutes often termed as osmotic solutes. A metabolite profiling of crude extracts of mature pear leaves of a range of 8 Pyrus genotypes was performed using current HPLC, UPLC and 1H NMR spectroscopy techniques in order to identify such putative compounds. Using as variables the concentrations of 45 identified substances and those of a restricted number of unknowns, all belonging to LMW carbohydrates, polyols, organic acids, amino acids and phenolics on the one hand, and the varieties investigated as individuals on the other, we generated a set of data analyzed further by PCA. Those varieties were discriminated into three clusters respectively comprised of the four Asian varieties, the European variety Williams grafted onto 4 different rootstocks, and the two other European varieties Conference and Angelys. These metabolic phenotypes were shown to rely more on scion genotypes than on rootstocks. High to very high amounts of sorbitol (average content of 363 μmol g−1 DW) associated with low amounts of mannitol and myo-inositol were found in all genotypes as well as in a local ecotype of P. communis where the hexitol accounted for 7.3% DW. Sorbitol actually represented up to 30-40% of the total osmotically active organic solutes accumulated in the set of pear leaves investigated, and it was shown to be significantly more abundant in the variety Williams than in Asian ones (p < 0.01). In contrast, the other well-known compatible solute glycine betaine, barely detectable using 1H NMR spectroscopy or HPLC, occurred in leaves of all pear varieties at weak levels lower than 2 μmol g−1 DW which suggested a minor role in osmotic adjustment. Its amount does not seem to be altered in response to an osmotic upshift applied to detached leaves or to depend on exogenously supplied ABA. For non-sustantiated reasons, these results are in contrast with those showing elsewhere very high accumulation of GB in the Asian genotype Su li. In this study mature leaves of this genotype collected from the same tree in July 2007 and July 2006 were shown to contain respectively 0.59 ± 0.04 and 0.85 ± 0.04 μmol g−1 DW. Other abundant organic substances like arbutine, quinic acid, malic acid, sucrose as well as chlorogenic acid and other quinic acid adducts, might also behave as osmotically active substances. In addition to arbutine, its derivative hydroquinone, chlorogenic acid and structurally related substances might be involved in protective functions against secondary oxidative stresses induced by abiotic and biotic stresses encountered during the growing season

Metabolome and water homeostasis analysis of Thellungiella salsuginea suggests that dehydration tolerance is a key response to osmotic stress in this halophyte

International audienceP>Thellungiella salsuginea, a Brassicaceae species closely related to Arabidopsis thaliana, is tolerant to high salinity. The two species were compared under conditions of osmotic stress to assess the relationships between stress tolerance, the metabolome, water homeostasis and growth performance. A broad range of metabolites were analysed by metabolic fingerprinting and profiling, and the results showed that, despite a few notable differences in raffinose and secondary metabolites, the same metabolic pathways were regulated by salt stress in both species. The main difference was quantitative: Thellungiella had much higher levels of most metabolites than Arabidopsis whatever the treatment. Comprehensive quantification of organic and mineral solutes showed a relative stability of the total solute content regardless of the species or treatment, meaning that little or no osmotic adjustment occurred under stress. The reduction in osmotic potential observed in plants under stress was found to result from a passive loss of water. Thellungiella shoots contain less water than Arabidopsis shoots, and have the ability to lose more water, which could contribute to maintain a water potential gradient between soil and plant. Significant differences between Thellungiella and Arabidopsis were also observed in terms of the physicochemical properties of their metabolomes, such as water solubility and polarity. On the whole, the Thellungiella metabolome appears to be more compatible with dehydration. Osmotic stress was also found to impact the metabolome properties in both species, increasing the overall polarity. Together, the results suggest that Thellungiella copes with osmotic stress by tolerating dehydration, with its metabolic configuration lending itself to osmoprotective strategies rather than osmo-adjustment

Potentiation of proline accumulation in oilseed rape leaf discs exogenously supplied with combinations of PEG and cryoprotective agents is associated with overproduction of ABA

International audiencePhysiological processes involved in the control of the magnitude of the stress-induced proline (Pro) response of higher plants are not fully understood. Here we are dealing with Pro accumulation by rape leaf discs (RLDs) treated in vitro, under light conditions, with dual unusual systems containing low concentrations of the non-permeant polymer PEG 6000 (PEG) added with readily permeant cryoprotective agents (CPAs). At osmotically active concentrations, dimethylsulfoxide (DMSO), glycerol, 1,3-propanediol, ethylene glycol and dimethylformamide (DMF) behaved as very poor inducers of the Pro response when provided alone. On the contrary when all those substances (apart DMF) were supplied at onset of treatments, in combination with PEG, Pro levels greatly exceeded what could be predicted through simple additivity of the effects of those substances provided individually. This suggested potentiation effects at the level of some component(s) of Pro metabolism involved in stress-induced Pro accumulation. We have also demonstrated that exogenous ABA could substitute for DMSO (but not PEG), this other binary system also inducing (through potentiation) high rate of Pro accumulation. The strinking similarity between the responses induced with PEG + DMSO and PEG + ABA suggested that DMSO induced increases in the endogenous amount of ABA which might be, at its turn, acting as exogenously supplied ABA. Additional amounts of ABA actually accumulated in leaf discs treated with the dual system PEG + DMSO. Other CPAs tested in this study, except dimethylformamide (DMF), might also be acting on the same way. Potentiating effects, associated with enhanced amount of ABA, were also found to result from combinations of PEG with a range of organic and inorganic substances which mimick to some extent the cytosolute composition of plant cells. Together, our results gain some insight into the physiological mechanisms involved in the control of stress-induced Pro accumulation and strongly suggest their relationship with stress-induced changes in ABA content. (C) 2012 Elsevier B.V. All rights reserved