Estimation of the Relative Sizes of the Two NPQ-Associated Dissipations in Rice

Abstract

In photosystem II (PSII), light energy absorbed in chlorophyll a is de-excited not only through electron transport but through basal dissipation and non-photochemical quenching (NPQ)-associated dissipation. NPQ consists of energy-dependent quenching (qE) and the other unknown quenching (designated as qU). Whereas the quantum yields of electron transport, basal dissipation and NPQ-associated dissipation have been estimated with the pulse amplitude modulation (PAM) fluorometer by several groups, the exact ratio of two NPQ-associated dissipations, qE-associated and qU-associated dissipations, have not been estimated yet. Here, we estimated the relative rate constant for qU associated dissipation (kqU) in PsbS-silenced lines (qE knockdown) of rice from the fraction of NPQ, based on the lake model of energy transduction in PSII. The relative kUin the PsbS-silenced lines showed light-dependent increase. In the wild type, the relative rate constant of qE-associated dissipation was approximately three (in low light condition) and six (in high light condition) times as much as that of qU-associated dissipation. It is concluded that the qU-associtaed dissipation is light-inducible process and that the qE-associated dissipation is a major process of NPQ-associated dissipation in rice.