Photosynthetic CO2 assimilation, chlorophyll fluorescence and photoinhibition as affected by nitrogen deficiency in maize plants.

摘要

Effects of nitrogen deficiency on photosynthetic CO2 assimilation, photosystem II (PSII) photochemistry and photoinhibition were investigated in maize cv. Yedan 13 plants grown under natural illumination. Nitrogen-deficient plants had a significantly smaller CO2 assimilatory capacity, but they showed little changes in the maximal efficiency of PSII photochemistry, the rate of QA reduction and the heterogeneity of PSII reaction centres, suggesting that nitrogen deficiency had little effect on PSII primary photochemistry and photoinhibition even under natural illumination. However, modifications in PSII photochemistry under steady state photosynthesis induced by nitrogen deficiency were observed. This is reflected in decreases in the quantum yield of PSII electron transport, the efficiency of excitation energy capture by open PSII reaction centres, and the photochemical quenching coefficient and an increase in the non-photochemical quenching coefficient. These results suggest that modifications ofPSII photochemistry under steady state photosynthesis may be a mechanism to downregulate photosynthetic electron transport so that production of ATP and NADPH would be in equilibrium with the decreased demand in the Calvin cycle in nitrogen-deficient plants. On the other hand, the nitrogen-deficient plants still exhibited increased susceptibility to photoinhibition when exposed to very high irradiance, although nitrogen deficiency induced no photoinhibition under natural illumination. It is suggested that such increased susceptibility to photoinhibition was associated with the increased accumulation of inactivated PSII reaction centres, the decreased capacity of non-photochemical quenching, and the increased fraction of the reduction state of QA.