Plasticity of photosynthetic metabolism in Jatropha curcas genotypes under water deficit
With the advent of the Brazilian Government Biodiesel Program and the increasing demand for vegetable oils, Jatropha curcas has been emphasized as an alternative raw material. Given the known water stress tolerance of this species, we evaluated the plasticity of photosynthetic metabolism in nine genotypes of J. curcas under water stress (WS). The hypotheses that (1) the photosynthetic metabolism of J. curcas is plastic and changes towards crassulacean acid metabolism (CAM) according to water availability and (2) the plasticity of the metabolic alteration is variable among the different genotypes and is related to physiological adjustments, were tested. Water deficit led to 167 and 187% increase in phosphoenolpyruvate carboxylase (PEPC) activity in leaves collected at 4 and 16 h,, respectively, when compared to control plants. The accumulation of organic acids (malate and citrate) differed among genotypes and WS treatments. There was an average increase of 270% for plants submitted to WS, when citrate was compared to malate. There was an increase of 62% in total soluble sugar content and a decrease of 27% in starch content in plants under WS when compared to controls. Significant effects of genotype and watering regime were detected for carbon isotope composition of leaf biomass. We detected changes in photosynthetic metabolism towards low CAM levels, thus explaining the maintenance of efficiency of water use under water deficit.