PARENT SESSION

Symposium S2B Light, redox and metabolic regulation: Light reactions
Monday August 30th, 2004 2:40 PM-4:40 PM Room 210A
Chair: Frances-Andre Wollman
Co-Chair: Kris Niyogi

The importance and evolution of feedback de-excitation. Stefan Jansson^*,, Carsten Külheim¹, Jenny Andersson¹, Oskar Skogström¹, Peter Horton, Krishna Niyogi, Jon Ågren, ¹ Umeå Plant Science Centre, Umeå, Sweden

ABSTRACT- Feedback de-excitation, also called the qE type of non-photochemical quenching, is a process that regulates photosynthetic light harvesting. Two proteins have been found to be essential for feedback de-excitation, violaxanthin deepoxidase (VDE) converts violaxanthin to zeaxanthin and PsbS, that in a way not yet completely understood changes conformation after low pH-induced protonation and zeaxanthin binding. Mutants lacking VDE (npq1) or PsbS (npq4) perform under laboratory conditions as well as wildtype plants, but under field conditions Darwinian fitness of the plants are drastically reduced, showing that feedback de-excitation has a large adaptive significance. We have also shown that a likely cause of this lowered fitness is reduced capacity to cope with fluctuations in light. We have now subjected wt, npq1 and npq4 plants grown in the field and in the lab under constant and fluctuating light conditions to a detailed analysis of their photosynthetic performance. Under fluctuating light in otherwise constant conditions, the plants seem to acclimate by reducing the photosynthetic capacity while plants grown under field conditions, photoinhibitions leads to costs for repair and also to earlier senescence, perhaps due to an increased ROS production, resulting in reduced fitness. We have also noted an increased fitness of Arabidopsis overexpressing PsbS, and we have done studies on the regulation of the PsbS gene. In addition, we have created transgenic Populus trees lacking PsbS due to RNAi, and initiated a fucntional analysis of these trees. These results will be discussed in an evolutionary context.

KEY WORDS: NPQ, Arabidopsis, Fitness