Reversible Effects of High, Sublethal Temperatures on Light-Induced Light Scattering Changes and Electrochromic Pigment Absorption Shift in Spinach Leaves

Abstract

Summary Intact spinach leaves were subjected to high but sublethal temperatures (3 min at 40°C or 0.5–4 h at 34°C). The alterations which occured at the thylakoid membrane have been investigated by analysis of light induced absorption changes around 518 and 535 nm. The dark decay of a slow absorption change peaking at 535 nm was accelerated after heating whereas the amplitude was strongly enhanced at wavelengths lower than 520 nm indicating a modulation of kinetic and spectral characteristic of light induced light scattering changes of thylakoid membranes. Fast absorption changes after 1 min illumination showing the spectral characteristic of the electrochromic absorption shift of thylakoid pigments was lowered by heating; the dark decay of the electrochromic shift after a 1 ms flash was accelerated. The heat induced alterations of absorption changes disappeared within 20–30 min after lowering the temperature to 20°C and was accompanied by a reversible decrease of photosynthetic CO 2 , uptake by leaves. The heat effect on the electrochromic shift observed after 30 min exposure to 34°C disappeared after prolonged exposure (1–4 h) to this temperature indicating an increase in thermostability of thylakoid membranes. The results are discussed in terms of heat induced alterations of thylakoid membrane structure leading to increased ion fluxes across the membrane during illumination. It is discussed whether the temperature sensitivity of thylakoid membrane interferes with the regulation of photosynthesis and starts the process of acclimation.