Plants under Climatic Stress: III. Low Temperature, High Light Effects on Photosynthetic Products.

An investigation has been made of the combined effects of low temperature and high light on the level of several photosynthetic products in the leaves of a group of plants differing widely in their tolerance to this stress. Starch levels in these plants after chilling are dependent on the time of day that temperatures are lowered and seem related to rates of CO(2) assimilation under this stress. Prolonged low-temperature, high-light treatment (10 C at 160 wm(-2)) of Sorghum bicolor induced a rapid starch hydrolysis after a lag of some 24 hours. Differing rates of starch loss at the cellular level and a rapid migration of chloroplasts toward the base of upper mesophyll cells were also seen in leaves of this stress-sensitive species.Chilling increased the level of almost all free amino acids in tolerant and in semi-tolerant species, while amino acids related to intermediates of the C(4)-pathway show a sharp or transitory decrease in Sorghum. These and other changes observed in Sorghum suggest that some time- and temperature-dependent blockages develop in the interconversion of C(4)-pathway intermediates and possibly in the flow of other intermediates to and from the sites of C(4)-photosynthesis.Levels of ATP in the leaves of Sorghum, Paspalum, and Amaranthus increased at night and following chilling and did not fall until pronounced necrosis of the leaves commenced.