Study of polyphasic fluorescence induction in Lemna minor in the presence of methyl viologen (MV) and duroquinone (DQ)

Abstract

Polyphasic fluorescence kinetics induced by saturating flash were investigated at different fluorescence induction states. Chlorophyll a fluorescence kinetic induction was simultaneously analyzed by Pulse Amplitude Modulated and Plant Analyzer Efficiency spectrofluorometers. Rapid fluorescence rise was induced in dark-adapted leaves, in the presence of modulated light non-triggering photochemical effect, at the steady-state fluorescence inducted by actinic light and in the presence of far-red light. Under those experimental conditions chlorophyll fluorescence transients were examined at O-J-I-P states. At all sites of examinated fluorescence induction of control plants we were able to identify the O-J-I-P transients. When the electron transport was interfered with DQ, the fluorescence yield at P level at every successive flash was increased and the rapid transients were not appearing. However, when MV was used as an efficient oxidizing exogen electron acceptor, the fluorescence yield at maximum level (P transient) was gradually decreased but the fluorescence transients O, J and I were distinguished. We noticed a progressive fluorescence rise at the time-course close to K transient. At this state, it was not possible to identify does the increase of the fluorescence yield at initial state was due to appearance of new fluorescence transient or caused by QA- accumulation at early stage of PSII photochemistry. However, the large differences in rapid fluorescence rise in the presence of DQ or MV were noticed compared to the control plant. It appears that differences do not derive only from the change of the electron transport oxydo-reduction state but also from structural change of PSII complex.