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

Maize plants were grown at 14, 18 and 20 degrees C until the fourth leaf ha d emerged. Leaves from plants grown at 14 and 18 degrees C had less chlorop hyll than those grown at 20 degrees C. Maximal extractable ribulose-1,5-bis phosphate carboxylase/oxygenase (Rubisco) activity was decreased at 14 degr ees C compared with 20 degrees C, but the activation state was highest at 1 4 degrees C. Growth at 14 degrees C increased the abundance (but not the nu mber) of Rubisco breakdown products. Phosphoenolpyruvate carboxylase (PEPC) activity was decreased at 14 degrees C compared with 20 degrees C but no c hilling-dependent effects on the abundance of the PEPC protein were observe d. Maximal extractable NADP-malate dehydrogenase activity increased at 14 d egrees C compared with 20 degrees C whereas the glutathione pool was simila r in leaves from plants grown at both temperatures. Foliar ascorbate and hy drogen 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 CO 2 fixation together with decreased quantum efficiencies of photosystem (PS) II in the light, although there was no photo-inhibition. Growth at 14 degr ees C decreased the abundance of the D1 protein of PSII and the PSI psaB ge ne product but the psaA gene product was largely unaffected by growth at lo w temperatures. The relationships between the photosystems and the co-ordin ate regulation of electron transport and CO2 assimilation were maintained i n plants grown at 14 degrees C.