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

Effects of in vivo jasmonic acid (JA)-treatments on the photosynthetic apparatus of barley chloroplasts were studied by chlorophyll fluoresc ence 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 chloropla sts. This effect is most pronounced at an exogenous JA concentration o f 10(-4) M. Concomitant with this the F695/F685 ratio is enhanced in J A-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 fluore scence ratio F(v)/F(m) exhibits a certain decrease in chloroplasts iso lated from JA-treated plants. These data are discussed in terms of pos sible involvement of JA-induced alteration at the level of supramolecu lar organization of the thylakoid membranes.