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Analysis of Qualitative Contribution of Assimilatory and Non-Assimilatory De-Excitation Processes to Adaptation of Photosynthetic Apparatus of Barley Plants to High Irradiance

2000; Institute of Experimental Botany of the Czech Academy of Sciences; Volume: 38; Issue: 4 Linguagem: Inglês

10.1023/a

1573-9058

Irena Kurasová, M. Čajánek, J. Kalina, Vladimı́r Špunda,

Plant Water Relations and Carbon Dynamics

The adaptation of barley (Hordeum vulgare L. cv. Akcent) plants to low (LI, 50 µmol m-2 s-1) and high (HI, 1000 µmol m-2 s-1) growth irradiances was studied using the simultaneous measurements of the photosynthetic oxygen evolution and chlorophyll a (Chl a) fluorescence at room temperature. If measured under ambient CO2 concentration, neither increase of the oxygen evolution rate (P) nor enhancement of non-radiative dissipation of the absorbed excitation energy within photosystem 2 (PS2) (determined as non-photochemical quenching of Chl a fluorescence, NPQ) were observed for HI plants compared with LI plants. Nevertheless, the HI plants exhibited a significantly higher proportion of QA in oxidised state (estimated from photochemical quenching of Chl a fluorescence, qP), by 49-102 % at irradiances above 200 µmol m-2 s-1 and an about 1.5 fold increase of irradiance-saturated PS2 electron transport rate (ETR) as compared to LI plants. At high CO2 concentration the degree of P stimulation was approximately three times higher for HI than for LI plants, and the irradiance-saturated P values at irradiances of 2 440 and 2 900 µmol m-2 s-1 were by 130 and 150 % higher for HI plants than for LI plants. We suggest that non-assimilatory electron transport dominates in the adaptation of the photosynthetic apparatus of barley grown at high irradiances under ambient CO2 rather than an increased NPQ or an enhancement of irradiance-saturated photosynthesis.