Activation of Photorespiration Facilitates Drought Stress Tolerance in Lotus corniculatus

Photorespiration is the process that recycles 2-phosphoglycolate back to 3-phosphoglycerate resulting from the oxygenase activity of Rubisco. Recent studies proved the importance of photorespiration for plant survival under stress conditions, including drought stress. In the present study, physiological, biochemical and molecular responses of a moderately drought-tolerant plant Lotus corniculatus to PEG-mediated drought stress were examined. Growth, stomatal conductance (g(s)), maximum quantum yield of photosystem II (Fv/Fm), CO2 assimilation (A), electron transport (ETR) and transpiration rates (E) were decreased, whilst intercellular CO2 concentrations (Ci), non-photochemical quenching (NPQ) and photorespiration rates were increased in the drought stress-exposed plants. Activities and expression profiles of photorespiratory cycle enzymes correlated well with the increased photorespiration rates. In the line of our results, we conclude that the activation of photorespiration for recycling 2-phosphoglycolate (2PG) to chloroplast facilitated the maintenance of growth and drought stress tolerance in L. corniculatus. Accordingly, we can speculate that drought stress exerted by PEG20 (20% PEG6000) with an osmotic pressure of -0.73 MPa may be a threshold level for drought tolerance in L. corniculatus since the long-term effects of PEG20 on tolerance-related parameters (RGR, membrane integrity, leaf water status and photosynthesis) were more remarkable.