EFFECT OF ULTRAVIOLET-RADIATION ON STRUCTURAL-FUNCTIONAL CHARACTERISTICS OF THE THYLAKOID MEMBRANE

We used the EPR method to study the action of UV radiation (290-330 nm ) on membrane structural characteristics and chloroplast photochemical activity. It is demonstrated that UV irradiation suppresses photochem ical activity of photosystem II, lowering the flow of electrons betwee n the photosystems in the process. Photosystem I here turns out to be less sensitive to the harmful action of UV irradiation. Use of the spi n probe method to investigate thylakoid membrane structural characteri stics revealed that exposure to UV causes no significant changes in st ructural organization of the lipid regions of those membranes. On the other hand, UV irradiation leads to significant increase in value of t he surface potential of the thylakoid membrane. Ultraviolet irradiatio n of isolated thylakoid membranes and subchloroplast fragments of PSII is accompanied by increase in the six-component EPR signal of activat ed Mn2+. It is hypothesized that the complex of water photodegradation is the sector of PSII most sensitive to UV irradiation in isolated ch loroplasts and their fragments.