Abstract
Regulation of photosynthetic electron transport was studied in intact leaves on the basis of the low-wave phenomenon, i.e. the transient drop of yield of modulated chlorophyll fluorescence shortly after application of a pulse of saturating light. Measurements of chlorophyll fluorescence, CO2 uptake and absorption at 830 nm of leaves showed that low-waves of chlorophyll fluorescence are induced by increased non-photochemical quenching as a result of induction of cyclic electron flow around photosystem I (PSI). It was suggested from observations of low-waves that cyclic PSI plays a role in the regulation of the rate of photosynthetic electron transport by increasing thermal dissipation of excess excitation energy in photosystem II. PSI cyclic flow, however, was not induced under the conditions where incident light intensity was so high as to fully saturate photosynthesis (e.g. at 1,100 μmol photon m-2s-1 in normal air).
