CHLOROPHYLL FLUORESCENCE PROPERTIES OF CHLOROPLAST MEMBRANES ISOLATED FROM JASMONIC ACID-TREATED BARLEY SEEDLINGS

Effects of in vivo jasmonic acid (JA)-treatments on the photosynthetic apparatus of barley chloroplasts were studied by chlorophyll fluorescence measurements. Low temperature (77K) fluorescence emission spectra indicate that the peak at 735 nm originating from photosystem I (PSI) is considerably reduced and the F735/F695 ratio is markedly lower in chloroplasts isolated from JA-treated plants than in control chloroplasts. This effect is most pronounced at an exogenous JA concentration of 10(-4) M. Concomitant with this the F695/F685 ratio is enhanced in JA-treated chloroplasts, the effect being also concentration dependent. It is demonstrated that chlorophyll a fluorescence levels (F(o), F(m)) are also increased to 160% and 123%, respectively, as a result of JA (10(-4) M) treatment. However, the variable fluorescence (F(v) = F(m) = F(o)) remains almost constant under the same conditions. The fluorescence ratio F(v)/F(m) exhibits a certain decrease in chloroplasts isolated from JA-treated plants. These data are discussed in terms of possible involvement of JA-induced alteration at the level of supramolecular organization of the thylakoid membranes.