Physiological and biochemical responses of common bush bean to drought

Abstract

Agriculture has been adversely affected by the low water availability resulting from climate change, creating environmental stress for the common bean (Phaseolus vulgaris L.). A growth room experiment was performed to evaluate the physiological and biochemical responses of the several bush bean genotypes to water deficit conditions. Plants in soil with 20 g·L-1 polyethylene glycol 6000 (PEG) were subjected to drought for 15 d. The levels of photosynthesis, stomatal conductance and transpiration in all genotypes decreased by approximately 65% under water deficit conditions compared with the corresponding values in the controls. Water use efficiency was enhanced by water deficit conditions, with 'Bianca' plants exhibiting the highest values (28.08 μmol·mol-1), followed by 'NUA35', 'Bachue' and 'Cerinza' (20.46, 20.11 and 18.21 μmol·mol-1, respectively). The 'Bianca' plants exhibited a lower relative tolerance index (50%), and water deficit increased the levels of leaf photosynthetic pigments, chlorophyll and carotenoids in this genotype by approximately 100%. The photosynthetic efficiency, which was evaluated using the Fv/Fm ratio and rapid light-derived parameters (the maximum electron transport rate and a light saturation parameter), decreased due to water deficit conditions, particularly in the 'Bianca' plants, in which these parameters were reduced by approximately 60%. The proline and malondialdehyde (MDA) contents were increased by the addition of PEG, primarily in the 'Bacatá' and 'Bianca' plants. In conclusion, our results suggest that rapid light-response curves can be useful for characterizing genotypes because they represent an easy and non-destructive tool for understanding acclimatization mechanisms under water deficit conditions. In addition, all genotypes exhibited susceptibility to water deficit conditions, and the most susceptible genotype was 'Bianca', as reflected by a significant reduction in the electron transport rate and the presence of oxidative damage (high MDA content and electrolyte leakage), suggesting that this cultivar could not adapt well to landscaping situations in which periods of extreme water deficit can be expected.