Poster: Photosynthesis

Abs # 353: Causal Factors for Reversible Lowering of Modulated Chlorophyll Fluorescence after Saturating Pulse

Presenter:	Tsuyama, Michito , mtu@agr.kyushu-u.ac.jp
Authors	Tsuyama, Michito  (A)   Kawazu, Tetsu  (A)   Kobayashi, Yoshichika  (B)
Affiliations:	(A): Forestry Research Institute, Oji Paper Company Limited (B): Department of Plant Resources, Kyushu University

A low-wave phenomenon, transient lowering in chlorophyll fluorescence induced after application of saturating pulse of white light, was investigated in intact leaves by measuring gas exchange and 830-nm absorption simultaneously. Low waves were observed during induction of photosynthesis in normal air conditions (21 % O₂ and 350 ppm CO₂) under intermediate light (e.g., 226 mmol photon m^-2s^-1), but disappeared during steady-state photosynthesis. Low waves could also be detected in steady-state conditions by reducing CO₂ concentration in air over a wide range of photon flux densities from 96 to 1094 mmol photon m^-2s^-1. The low-wave phenomenon was found to occur in parallel with a large increase in non-photochemical fluorescence quenching. However, under high light (> 418 mmol photon m^-2s^-1) where non-photochemical quenching of chlorophyll fluorescence reached saturation, amplitude of low wave became very small. Low waves could also be induced by severe acceptor limitation of linear electron transport which was forced by illuminating leaves in CO₂-free air with 1 % O₂. These results suggest that a saturating pulse caused considerable increase in radiationless dissipation of light energy under acceptor limitation of linear electron transport, thereby inducing low waves of chlorophyll fluorescence. An involvement of PSI-dependent cyclic electron transport in low-wave phenomenon was also suggested from redox changes of P700 (the reaction center of photosystem I) monitored as absorbance changes in the 830-nm region.