ABA increases the desiccation tolerance of photosynthesis in the afromontane understorey moss Atrichum androgynum

The effect of pretreatment with abscisic acid (ABA) on the physiology of the moss Atrichum androgynum during a desiccation-rehydration cycle was examined. During rehydration following desiccation for 16 h. net CO. fixation recovered much more slowly than photosystem II (PSII) activity, conditions conducive to the formation of reactive oxygen species (ROS) in the photosynthetic apparatus, Pretreatment with ABA increased the rate of recovery of photosynthesis and PSII activity, and also doubled non-photochemical quenching (NPQ). Increased NPQ activity will reduce ROS formation, and may explain in part how ABA hardens the moss to desiccation. In ABA-pretreated, but not untreated mosses, desiccation significantly increased the concentration of soluble sugars. Sugar accumulation may promote nitrification of the cytoplasm and protect membranes during desiccation. Starch concentrations in freshly collected A. androgynum were only approx. 40 mg g(-1) dry mass; they rose slightly during desiccation but were only slightly affected by ABA pretreatment. ABA did not reduce chlorophyll breakdown during desiccation. (C) 1001 Annals of Botany Company.