Plants under Climatic Stress: VI. Chilling and Light Effects on Photosynthetic Enzymes of Sorghum and Maize

The activity of several photosynthetic enzymes was unaltered by exposure of sorghum or maize to low temperatures (10 C) and light (170 w m⁻²). Two light-activated C₄-pathway enzymes, NADP-malate dehydrogenase and pyruvate Pi dikinase, were reduced in activity, and this was largely attributable to a loss of enzyme rather than to incomplete enzyme activation. Loss of NADP-malate dehydrogenase was more marked in sorghum than in maize, and in both species no loss occurred at 10 C when light levels were reduced from 170 to 50 w m⁻². A light-dependent, low temperature-induced loss of catalase activity was also observed in maize leaves.