Unravelling the roles of desiccation-induced xanthophyll cycle activity in darkness: a case study in Lobaria pulmonaria.

Desiccation-tolerance ability in photosynthetic organisms is largely based on a battery of photoprotective mechanisms. Xanthophyll cycle operation induced by desiccation in the absence of light has been previously proven in the desiccation-tolerant fern Ceterach officinarum. To understand the physiological function of xanthophyll cycle induction in darkness and its implication in the desiccation tolerance in more detail, we studied its triggering factors and its photochemical effects in the lichen Lobaria pulmonaria. We found that both the drying rate and the degree of desiccation play a crucial role in the violaxanthin de-epoxidase activation. De-epoxidation of violaxanthin to zeaxanthin (Z) occurs when the tissue has lost most of its water and only after slow dehydration, suggesting that a minimum period of time is required for the enzyme activity induction. Fluorescence analysis showed that Z, synthesised during tissue dehydration in the absence of light, prevents photoinhibition when rewatered tissues are illuminated. This is probably due to Z implication in both non-photochemical quenching and/or antioxidative responses.