Survival strategies of plants during water stress

Fluorescence and gas exchange of bean, maize, sunflower and wooly foxglove were simultaneously measured at 250 μmol quanta/m2/s. Under severe water stresses conditions about 40% of the photochemical energy was converted to heat at PS II. This is interpreted as a protective mechanism against photoinhibitory damage when net CO2 uptake is reduced by about 70%. After 14CO2 gas exchange, only in bean was a homogeneous distribution of radioactivity over the leaf observed. In all other plants we found a patchy distribution of regions with either an intensive or a reduced gas exchange. We conclude that CO2-recycling (photorespiration and reassimilation) behind closed stomata also contributed to energy dissipation under severe stress conditions