Abstract
The photosynthetic electron transfer chain generates proton motive force (pmf) across thylakoid membranes, and the balancing the pmf is important for acclimation to environmental challenges. In this study, a change in the absorption spectra of carotenoid pigments in the thylakoid membranes, the so-called "electrochromic shift (ECS)" was analyzed to gain information on the energy balance in the thylakoid membrane of wild watermelon under drought/high light stresses. Proton flux across thylakoid membranes were estimated from dark-interval relaxation kinetics (DIRK) analysis, and plotted against electron transfer rate (ETR) from photosystem II. The analysis revealed that the slope of proton flux vs. ETR was significantly larger in the leaves under drought than that in the irrigated controls, suggesting the activation of cyclic electron flow around photosystem I under drought stress.
