Effects of anaerobiosis as probed by the polyphasic chlorophyll a fluorescence rise kinetic in pea (Pisum sativum L.)

We analysed the changes of the chlorophyll (Chl) a fluorescence rise kineti c (from 50 mu s to 1 s) that occur when leaves or chloroplasts of pea ( Pis um sativum L.) are incubated under anaerobic conditions in the dark. In con trol leaves, Chl a fluorescence followed a typical O-J-I-P polyphasic rise [Strasser et al. (1995) Photochem Photobiol 61: 32-42]. Anaerobiosis modifi ed the shape of the transient with the main effect being a time-dependent i ncrease in the fluorescence yield at the J-step (2 ms). Upon prolongation o f the anaerobic treatment (> 60 min), the O-J-I-P fluorescence rise was eve ntually transformed to an O-J (J = P) rise. A similar transformation was ob served when pea leaves were treated with DCMU or sodium dithionite. Anaerob iosis resulted in a 10-20% reduction in the maximum quantum yield of the pr imary photochemistry of Photosystem II, as measured by the ratio of the max imal values of variable and total fluorescence (F-V/F-M). When the leaves w ere returned to the air in the dark, the shape of the fluorescence transien t showed a time-dependent recovery from the anaerobiosis-induced change. Th e original O-J-I-P shape could also be restored by illuminating the anaerob ically treated samples with far-red light but not with blue or white light. Osmotically broken chloroplasts displayed under anaerobic conditions fluor escence transients similar to those observed in anaerobically treated leave s, but only when they were incubated in a medium comprising reduced pyridin e nucleotides (NADPH or NADH). As in intact leaves, illumination of the ana erobically treated chloroplasts by far-red light restored the original O-J- I-P transient, although only in the presence of methyl viologen. The result s provide additional evidence for the existence of a chlororespiratory path way in higher plant cells. Furthermore, they suggest that the J-level of th e fluorescence transient is strongly determined by the redox state of the e lectron carriers at the PS II acceptor side.