Multiple effects of chromate on the photosynthetic apparatus of Spirodela polyrhiza as probed by OJIP chlorophyll a fluorescence measurements

Chromate (Cr) decreases the growth of Spirodela polyrhiza. The fronds lost their pigments. The O-2 evolution was also decreased. The Cr effect was fou nd to be dose dependent. The toxic effects of Cr have further been studied on the photosynthetic activity of Spirodela polyrhiza by means of the chlor ophyll a (Chl a) fluorescence transient O-J-I-P. The Chl a fluorescence tra nsients were recorded in vivo with high time resolution and analyzed accord ing to the JIP-test which can quantify the photosystem II behavior. Cr trea ted plants show a decrease in yield for primary photochemistry, phi (Po). T he performance index of PSII, PIABS, which is the combination of the indexe s of three independent parameters, (1) the total number of active reaction centers per absorption (RC/ABS), (2) yield of primary photochemistry (phi ( Po)) and (3) efficiency with which a trapped exciton can move an electron i nto the electron transport chain (psi (0)), decreased due to Cr treatment. Chromate sensitivity varies within plant populations. In summary Cr affects several targets of PSII. More specifically, the main targets of Cr, accord ing to the JIP-test, can be listed as a decrease in the number of active re action centers and damage to the oxygen-evolving complex. (C) 2001 Elsevier Science Ltd. All rights reserved.