Photosynthetic responses in the inducible mechanisms of desiccation tolerance of a liverwort and a moss

Chlorophyll fluorescence was used to study the effect of hardening treatments on aspects of desiccation tolerance in the liverwort Dumortiera hirsuta and the moss Atrichum androgynum. After desiccation the recovery of PS2 was monitored during rehydration. We show that partial dehydration and ABA treatments can increase desiccation tolerance. In A. androgynum, the increased desiccation tolerance is accompanied by increased NPQ. However, hardening decreases the efficiency of photosynthesis in unstressed plants as well. In D. hirsuta, as for Atrichum, treatment with ABA greatly increased desiccation tolerance. D. hirsuta was much more responsive to ABA hardening than Atrichum. Unlike Atrichum, increased desiccation tolerance was not accompanied by increased NPQ and decreased PS2 efficiency. While partial dehydration hardening had little effect on the liverwort before stress, hardened plants displayed a moderate (22%) but significant improvement in PS2 activity 1 h following rehydration. As for the ABA hardening treatments, improved recovery of PS2 activity was not accompanied by increased NPQ, and NPQ was actually lower in hardened plants. Partial dehydration can increase tolerance in D. hirsuta, however, the increases were less than those induced by ABA. The mechanism of the hardening-induced increases in desiccation tolerance appear quite different in the two species