Regulation of photosynthesis and antioxidant metabolism in maize leaves at optimal and chilling temperatures: review

Maize ( Zea mays L.) is a chilling (below 15 °C) sensitive plant that shows little capacity to acclimate to low growth temperatures. Maize leaves are extremely sensitive to chilling injury, which usually results in premature leaf senescence. Leaves exposed to temperatures below 10 °C in the light show substantial inhibition of CO 2 assimilation and down-regulation of photosynthetic electron transport. However, the intrinsic relationships between the quantum efficiencies of photosystems I and II are not modified by chilling. Moreover, the integral relationships between non-cyclic electron transport and CO 2 fixation are similar in chilled and unchilled leaves. In this review we examine the roles and importance of photosynthetic regulation, carbon metabolism and antioxidant metabolism in determining the sensitivity of maize leaf photosynthesis to chilling. The distinct cellular localisation patterns of antioxidant enzymes such as glutathione reductase (EC 1.6.4.2) and dehydroascorbate reductase (EC 1.8.5.1) can restrict the recycling of antioxidants associated with photosynthesis during chilling. Disruption of circadian regulation of metabolism and insufficient antioxidant defence are postulated to cause chilling sensitivity.