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 kinetic (from 50 mu s to 1 s) that occur when leaves or chloroplasts of pea ( Pisum sativum L.) are incubated under anaerobic conditions in the dark. In control leaves, Chl a fluorescence followed a typical O-J-I-P polyphasic rise [Strasser et al. (1995) Photochem Photobiol 61: 32-42]. Anaerobiosis modified the shape of the transient with the main effect being a time-dependent increase in the fluorescence yield at the J-step (2 ms). Upon prolongation of the anaerobic treatment (> 60 min), the O-J-I-P fluorescence rise was eventually transformed to an O-J (J = P) rise. A similar transformation was observed when pea leaves were treated with DCMU or sodium dithionite. Anaerobiosis resulted in a 10-20% reduction in the maximum quantum yield of the primary photochemistry of Photosystem II, as measured by the ratio of the maximal values of variable and total fluorescence (F-V/F-M). When the leaves were returned to the air in the dark, the shape of the fluorescence transient showed a time-dependent recovery from the anaerobiosis-induced change. The original O-J-I-P shape could also be restored by illuminating the anaerobically treated samples with far-red light but not with blue or white light. Osmotically broken chloroplasts displayed under anaerobic conditions fluorescence transients similar to those observed in anaerobically treated leaves, but only when they were incubated in a medium comprising reduced pyridine nucleotides (NADPH or NADH). As in intact leaves, illumination of the anaerobically treated chloroplasts by far-red light restored the original O-J-I-P transient, although only in the presence of methyl viologen. The results provide additional evidence for the existence of a chlororespiratory pathway in higher plant cells. Furthermore, they suggest that the J-level of the fluorescence transient is strongly determined by the redox state of the electron carriers at the PS II acceptor side.