Effect of dehydration on the photosynthetic apparatus of sun and shade leaves of laurel forest trees

In this work we study the effect of reduction in relative water content (RW C) on the chlorophyll fluorescence induction kinetics as well as on the mem brane integrity, measured as electrolyte leakage, in sun and shade leaves o f three Canarian laurel forest trees. No differences were found among the s pecies and type of leaves, when the slow fluorescence kinetic parameters an d electrolyte leakage were analyzed, values deviated from the normal ones a t 70% and 40% RWC respectively. On the contrary, the photochemical efficien cy of PSII was affected at higher values of RWC in sun leaves (90% and 52% RWC depending on the species) than in shade ones (40% RWC). These results i ndicate that the susceptibility of PSII to water deficit is different depen ding on species and environmental conditions where the leaves develop.