The effect of prolonged light deprivation on ultrastructure, pigment composition and functions of photosynthetic apparatus of the resurrection plant Haberlea rhodopensis Friv. (Gesneriaceae) was studied. For this purpose, intact plants were kept in darkness for up to 6 months. Haberlea rhodopensis demonstrated extraordinary ability to preserve its photosynthetic machinery intact despite complete absence of light. During the first 4 weeks of light deprivation, we observed preservation of pigment content, chloroplast ultrastructure and a decrease in the rate of CO(2) assimilation. The signs of dark-induced senescence were observed only after the fourth week. This phase was characterized by decrease of pigment content, partial disintegration of chloroplast ultrastructure and by the development of photosystem II down regulation that includes the increases in non-photochemical fluorescence quenching, qN. In comparison with other plants like common bean and Arabidopsis, the processes of dark-induced senescence were very slow and the plants still can recover even after 6 months of light deprivation. We think these findings can open new opportunities for studying not only dark-induced senescence but also to investigate mechanisms determining tolerance to multiple stresses affecting integrity of photosynthetic apparatus.
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