Shared mechanisms of photoprotection in photosynthetic organisms tolerant to desiccation or to low temperature

Plants that are tolerant of extreme low temperatures, and plants that are tolerant of desiccation, face similar physiological challenges, as low temperatures often result in extracellular ice formation resulting in desiccation of cells. Desiccation due to either low temperatures or water loss leads to severe mechanical as well as oxidative stress, and plants tolerant to either low temperatures or desiccation utilize similar mechanisms to cope with the extreme stress. Key mechanisms to cope with the mechanical stressors associated with cellular crowding include accumulation of both non-reducing sugars as well as LEA proteins. Key mechanisms to cope with oxidative stress include increases in (or the ability to maintain) antioxidant capacity, as well as increased usage of thermal energy dissipation. During both stressors major reductions in photochemical efficiency are observed that correlate with dark retention of the xanthophyll pigments zeaxanthin and antheraxanthin, suggesting sustained forms of thermal energy dissipation persist in these extreme stress scenarios to cope with the increased excitation pressure. The focus of this review is to highlight the shared physiological mechanisms used in both stress scenarios, with a focus on the mechanisms of photoprotection.