UV-B AND UV-C IRRADIATION OF SPINACH PSII PREPARATIONS IN VITRO - IDENTIFICATION OF DIFFERENT FRAGMENTS OF THE D1 PROTEIN DEPENDING UPON IRRADIATION WAVELENGTH

摘要

We have investigated the effects of UV-B and UV-C radiation upon isolated spinach (Spinacia oleracea L.) photosystem II preparations both containing and lacking quinones. UV-B irradiation of both PSII core and reaction centre particles gives rise to a prominent 20 kDa C-terminal fragment of the D1 protein, as well as to a 12 kDa fragment. The smaller fragment would be associated with cleavage near the Q(B)site of PS II and the larger with a cleavage at or near helix II under conditions that produce damage of acceptor-side type under visible high light. In the case of UV-C irradiation, C-terminal fragments of 20 kDa and 10 kDa are produced in core particles, and in reaction centres fragments of 16, 12 and 10 kDa are found. UV-C irradiation is also associated with multiple cleavages. In the case of reaction centre particles, the damage caused by UV-C irradiation is similar to that caused by acceptor side overreduction by visible light. The results suggest that a common receptor/photosensitiser for UV-B irradiation is present in all types of PSII. For UV-C irradiation, the receptor/sensitiser differs between PSTI cores and reaction centres. We suggest that damage as a result of UV irradiation leads to structural instability of PSII and increased accessibility to proteolytic events. [References: 30]