Abstract
Summary Effects of in vivo jasmonic acid OA)-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.
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