Abstract
The susceptibility to photoinhibition changes with growth conditions. This has been ascribed to changes in ability of photoprotective mechanisms. Although many authors have studied various photoprotective mechanisms, their quantitative contribution to the susceptibility to photoinhibition is still unclear, partly due to that most of previous studies focused on only one or two photoprotective systems in each study. We have developed an experimental system, in which many photoprotective mechanisms are simultaneously evaluated. We used plants grown under different combination of nutrient and light availability, which realised different combination of abilities of photoprotective mechanisms. We used the model of Demmig-Adams (1996), in which energy partitioning to electron transport and heat dissipation is quantified. Excess energy, defined as the energy that was neither used for electron transport nor dissipated as heat, was strongly correlated with the rate of photoinactivation irrespective of growth conditions, suggesting that the excess energy causes photoinactivation.
