FACTORS ASSOCIATED WITH DEPRESSION OF PHOTOSYNTHETIC QUANTUM EFFICIENCY IN MAIZE AT LOW GROWTH TEMPERATURE

The photosynthetic productivity of maize (Zea mays) in temperate regio ns is often limited by low temperatures. The factors responsible for t he sensitivity of photosynthesis in maize to growth at suboptimal temp erature were investigated by measuring (a) the quantum yields of CO2 f ixation and photosystem II (PSII) photochemistry, (b) the pigments of the xanthophyll cycle, (c) the concentrations of active and inactive P SII reaction centers, and (d) the synthesis of core components of PSII reaction centers. Measurements were made on fully expanded leaves gro wn at 14 degrees C, both before and during the first 48 h after transf er of these plants to 25 degrees C. Our findings indicate that zeaxant hin-related quenching of absorbed excitation energy at PSII is, quanti tatively, the most important factor determining the depressed photosyn thetic efficiency in 14 degrees C-grown plants. Despite the photoprote ction afforded by zeaxanthin-related quenching of absorbed excitation energy, a significant and more persistent depression of photosynthetic efficiency appears to result from low temperature-induced inhibition of the rate at which damaged PSII centers can be replaced.