An analysis of the mechanism of the low-wave phenomenon of chlorophyll fluorescence

The low-wave phenomenon, i.e., the transient drop of yield of modulated chlorophyll fluorescence shortly after application of a pulse of saturating light, was investigated in intact leaves of tobacco and Camellia by measuring fluorescence, CO₂ assimilation and absorption at 830 nm simultaneously. Limitations on linear electron flow, due to low electron acceptor levels that were induced by low CO₂, induced the low waves of chlorophyll fluorescence. Low-wave amplitudes obtained under different CO₂ concentrations and photon-flux densities yielded single-peak curves when plotted as functions of fluorescence parameters such as ΦPS II (quantum yield of Photosystem II) and qN (coefficient of non-photochemical quenching), suggesting that low-wave formation depends on the redox state of the electron transport chain. Low waves paralleled redox changes of P700, the reaction center of Photosystem I (PS I), and an additional electron flow through PS I was detected during the application of saturating pulses that induced low-waves. It is suggested that low waves of chlorophyll fluorescence are induced by increased non-photochemical quenching, as a result of the formation of a trans-thylakoid proton gradient due to cyclic electron flow around PS I.