heat stress, photosystem II thermostability, pigment-protein complexes, circular dichroism spectroscopy

High temperature stress decreases photosynthetic assimilation through the inactivation of photosystem II (PSII), the most heat-sensitive component of the oxygen-evolving complex. We have recently found higher thermostability of spruce PSII photochemistry compared to such control plants as Arabidopsis species and barley. In this work, we have therefore attempted to describe the causes of this effect on the level of the organization of pigment-protein complexes (PPCs) in spruce thylakoid membranes using circular dichroism (CD) spectroscopy. We have confirmed higher maximum efficiency of PSII photochemistry (FV/FM) for spruce needles in comparison to barley leaves. Temperature-dependent CD spectra have also demonstrated higher (by about 6° C) PSII thermostability of chiral macro-organization of PPCs in spruce thylakoid membranes compared to those in barley.