ANTENNA SIZE DEPENDENCY OF PHOTOINACTIVATION OF PHOTOSYSTEM-II IN LIGHT-ACCLIMATED PEA LEAVES

Utilization of absorbed light energy by photosystem (PS) II for O-2 ev olution depends on the light-harvesting antenna size, but the role of antenna size in the photoinactivation of PSII seems controversial. To address this controversy, pea (Pisum sativum L.) plants were grown in low (50 mu mol m(-2) s(-1)) or high (650 mu mol m(-2) s(-1)) light. Th e doubled functional antenna size of PSII in low light allows each PSI I to utilize twice as many photons at given flash light energies for O -2 evolution. The application of a target theory to depict the photon dose dependency of PSII photoinactivation measured by repetitive-flash O-2 yield and the ratio of variable to maximal chlorophyll fluorescen ce indicates that photoinactivation of PSII is probably a single-hit p rocess in which repair or photoprotective mechanisms are only slightly involved. Furthermore, the exacerbation of photoinactivation of PSII with greater antenna size under anaerobic conditions strongly indicate s that photoinactivation of PSII depends on antenna size.