Acclimation of photosynthesis, H2O2 content and antioxidants in maize (Zea mays ) grown at sub-optimal temperatures

Maize plants were grown at 14, 18 and 20 degrees C until the fourth leaf had emerged. Leaves from plants grown at 14 and 18 degrees C had less chlorophyll than those grown at 20 degrees C. Maximal extractable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity was decreased at 14 degrees C compared with 20 degrees C, but the activation state was highest at 14 degrees C. Growth at 14 degrees C increased the abundance (but not the number) of Rubisco breakdown products. Phosphoenolpyruvate carboxylase (PEPC) activity was decreased at 14 degrees C compared with 20 degrees C but no chilling-dependent effects on the abundance of the PEPC protein were observed. Maximal extractable NADP-malate dehydrogenase activity increased at 14 degrees C compared with 20 degrees C whereas the glutathione pool was similar in leaves from plants grown at both temperatures. Foliar ascorbate and hydrogen peroxide were increased at 14 degrees C compared with 20 degrees C. The foliar hydrogen peroxide content was independent of irradiance at both growth temperatures. Plants grown at 14 degrees C had decreased rates of CO2 fixation together with decreased quantum efficiencies of photosystem (PS) II in the light, although there was no photo-inhibition. Growth at 14 degrees C decreased the abundance of the D1 protein of PSII and the PSI psaB gene product but the psaA gene product was largely unaffected by growth at low temperatures. The relationships between the photosystems and the co-ordinate regulation of electron transport and CO2 assimilation were maintained in plants grown at 14 degrees C.