Modification of photosystem II photochemistry in nitrogen deficient maize and wheat plants

Modification of PSII photochemistry in nitrogen deficient maize and wheat plants was investigated. Fluorescence quenching analyses showed that nitrogen deficiency induced decreases in the quantum yield of PSII electron transport, the efficiency of excitation energy capture by open PSII reaction centers, and the photochemical quenching, but an increase in the non-photochemical quenching. The analyses of the polyphasic rise of fluorescence transients demonstrated that nitrogen deficiency decreased the efficiency with which a trapped exciton can move an electron into the electron transport chain further than Q_A and the quantum yield of electron transport beyond Q_A, while it increased the absorption and trapping fluxes per PSII reaction center. Nitrogen deficiency also resulted in a decrease in the absorption, trapping and electron transport fluxes per leaf cross section as well as a decrease in the concentration of active PSII reaction centers. The comparisons between fluorescence parameters and photosynthetic CO₂ assimilation and growth rates suggest that fluorescence quenching analysis and the JIP test derived from the polyphasic rise of fluorescence transient can be a useful tool for assessing the physiological effects of N deficiency on plants.