Abstract
Measurement of the slow phase (the P-S-M-T phase) of the chlorophyll fluorescence induction (CFI) phenomenon is a prospective candidate for plant diagnosis in greenhouses. We applied a methodology, the consecutive measurements of photochemical efficiency of photosystem (PS) II (ΨPSII) and non-photochemical quenching (NPQ) during a CFI phenomenon, to clarify the contributions of photochemical and non-photochemical quenching to the slow phase of CFI curves in mature tomato leaves grown in a semi-commercial greenhouse. The ΨPSII increased significantly between the inflection points of P and S and decreased between the inflection points of S and M. On the other hand, the NPQ remained at low values during the inflections of P, S and M, but then increased exponentially. These results prove that the shape of the CFI curve during the inflections of P, S and M is predominantly determined by the changes in the status of the photosynthetic electron transport chain, and the shape of the CFI curve after the inflection of M is strongly regulated by non-photochemical quenching, especially of the xanthophyll cycle. Furthermore, the two CFI measurements conducted at an interval of nine days proved that the slight changes in the photosynthetic functions, i.e. decreases in the capacities of the photosynthetic electron transport and the xanthophyll cycle, are detectable by measuring the slow phase of the CFI phenomenon.
