ABA treatment increases both the desiccation tolerance of photosynthesis,and nonphotochemical quenching in the moss Atrichum undulatum

Pulse amplitude modulation fluorescence was used to investigate whether abscisic acid (ABA) pretreatment increases the desiccation tolerance of photosynthesis in the moss Atrichum undulatum. In unstressed plants, ABA pretreatment decreased the F_V/F_m ratio, largely as a result of an increase in F_o. This indicated a reduction in energy transfer between LHCII and PSII, possibly hardening the moss to subsequent stress by reducing the production of the reactive oxygen species near PSII. During desiccation, F₀, F_m, F_v/F_m, PSII, and NPQ and F₀ quenching declined in ABA-treated and nontreated mosses. However, during rehydration, F₀, F_m, F_v/F_m, and PSII recovered faster in ABA-treated plants, suggesting that ABA improved the tolerance of photosystem II to desiccation. NPQ increased upon rehydration in mosses from both treatments, but much more rapidly in ABA-treated plants; during the first hour of rehydration, NPQ was two-fold greater in plants treated with ABA. F₀quenching followed a similar pattern, indicating that ABA treatment stimulated zeaxanthin-based quenching. The implications of these results for the mechanisms of ABA-induced desiccation tolerance in A. undulatum are discussed.