Senescing leaves possess potential for stress adaptation: the developing leaves acclimated to high light exhibit increased tolerance to osmotic stress during senescence

Plants may experience environmental stress factors operating in nature either simultaneously or in sequence. In the study, we have acclimated the developing primary leaves of wheat seedlings to high light stress and examined their photosynthetic response to polyethylene glycol (PEG) mediated osmotic stress during different developmental phases including senescence. The high light acclimated leaves show higher level of total carotenoids as compared to their non-acclimated counterparts experiencing osmotic stress during senescence. They also exhibit greater membrane stability as indicated by the measurements of fluorescence polarisation and energy transfer efficiency in photosystem I (PSI) and Photosystem II (PSII). From the data of DCPIP photoreduction and pulse amplitude modulated (PAM) fluorimetry, a similar trend is observed for PSII photochemistry of the leaves experiencing osmotic stress during senescence. Our results may suggest that the stress adaptive potential induced by one stress during development is retained by the leaves and helps to mitigate another stress effect operating in sequence during another developmental phase, namely senescence.