Leaf Photosynthesis Under Drought Stress

Abstract

The photosynthetic apparatus is resistant to drought. Net uptake of a leaf submitted to a mild desiccation decreases because of stomatal closure. As a result, exposed to water shortage. This drop in the chloroplast concentration in the chloroplast decreases in plants concentration causes: (i) a decrease in photochemical yield of open PS II centers and, consequently, an increase of thermal dissipation of the excitons trapped in PS II units; (ii) a decline in the activity of some enzymes, e.g. sucrose phosphate synthase and nitrate reductase; (iii) an increase in the activity of ribulose 1,5-bisphosphate oxygenase. The water status of the plants can be maintained under fluctuating water supply through a regulation of waterloss and water uptake, in which abscissic acid plays a major role. The role of photorespiration in protecting the photosynthetic apparatus against high light damage is unclear. Leaf movements (paraheliotropism) and thermal dissipation of excitons trapped in PS II units are probably much more efficient mechanisms than photorespiration to protect photosystems against photoinhibition. Drought also causes large changes in carbon partitioning at the cellular and plant levels, and profound modifications in the composition of membrane proteins and lipids in the photosynthetic apparatus.