| Although light capture fuels growth and development of photosynthetic organisms, excess light absorption severely damages photosynthetic structures. A green alga, Chlamydomonas reinhardtii, responds to excess-light stress by down-regulating the light-harvesting complexes (LHCs) that surround and funnel absorbed energy into Photosystem II. Following transfer from low-light (LL) to high-light (HL), abundance of Lhcb transcripts (encoding LHCII proteins) declines but then rebounds to LL levels within 6 to 8 hours. However, LHC protein levels continue to decline, suggesting that antennae abundance may be translationally controlled, a possibility examined herein using polysome profiles. Initially following a LL to HL shift, Lhcb transcripts are off-loaded from polysomes; within 8 hours, however, the transcripts are loaded back onto polysomes, suggesting that translational repression recovers co-ordinately with the rebound of total Lhcb mRNA levels. Therefore, continual decline of antennae proteins during photo acclimation in HL is likely mediated by post-translational mechanisms such as protein turnover. |
