Light sensitivity of Haberlea rhodopensis shade adapted phenotype under drought stress

Haberlea rhodopensis belongs to the group of homoiochlorophyllous desiccation-tolerant plants which preserve their chlorophyll content during dehydration. It is a typical shade adapted plant and it is proved to be very sensitive to light intensity higher than the natural during drought stress. To reveal the reasons of their light sensitivity, we compared the damages and protective mechanisms of shade plants during desiccation either simulating their natural light conditions (30 mu mol photons m(-2) s(-1), LL) or at a moderately higher light intensity (100 mu mol photons m(-2) s(-1), ML). In the desiccated stage, no damage could be discovered in terms of thylakoid membrane quantity or integrity either at LL or ML. Nevertheless, the altered structure and localization of chloroplasts did not restore in plants desiccated and rehydrated at ML, where no starch could be re-synthesized, but a number of plastoglobuli appeared. The PSII activity and the amount of beta-carotene and lutein decreased more strongly in ML leaves in agreement with their higher MDA production. Lack of recovery of ML plants may be connected with the very high number of damaged PSII reaction centres caused by the loss of the subtle balance between ROS production and scavenging. In addition, because of the impaired starch re-synthesis, there is no sink for the water-replacing sugars and water cannot be taken up which proved to be lethal to ML plants.