Rapid photoprotection in sea‐ice diatoms from the East Antarctic pack ice

Abstract

Photoinhibition and D1 protein re‐synthesis were investigated in bottom‐dwelling sea‐ice microalgal communities from the East Antarctic pack ice during early spring. Bottom‐dwelling sea‐ice microalgal communities were dominated by diatoms that exhibited rapid photoprotection when exposed to a range of different light levels (10 µmol photons m−2 s−1, 50 µmol photons m−2 s−1, 100 µmol photons m−2 s−1, and 200 µ;mol photons m−2 s−1). Photosynthetic capacity of photosystem II (PSII) dropped significantly over 3 h under 200 −mol photons m−2 s−1, but largely recovered when placed in a low‐light environment (10 µmol photons m−2 s−1) for an additional 3 h. PSII repair rates increased with increasing irradiance, and the D1‐protein pool remained steady even under high light (200 µmol photons m−2 s−1). Sea‐ice diatoms showed a low intrinsic susceptibility to photoinactivation of PSII across all the light treatments, and a strong and irradiance‐dependent induction of nonphotochemical quenching, which did not depend upon chloroplast protein synthesis, was also seen. These highly plastic organisms, once thought to be adapted to shade, are in fact well equipped to withstand rapid and relatively large changes in light at low temperatures with minimal long‐term effect on their photosynthetic machinery.