Effect of Chilling on the Activity of Enzymes of the Photosynthetic Carbon Reduction Cycle

Abstract

Photosynthesis measured at the normal growth temperature for the chill-sensitive tomato is inhibited by 60% after plants experience a 1 °C cold treatment in the dark for 16 hours. While s tomatal closure is responsible for a portion of this reduction, the principle component of the injury is due to a direct inhibition of chloroplast activity (1). Other chill-sensitive species show a similar response, and it seems likely that in general approximately 2/3 of the chill-induced decrease of photosynthesis is due to an inhibition at the chloroplast level (2). The capacity for electron transport and ATP synthesis is not significantly reduced following a dark chilling treatment (3, 4). Therefore, the reduction in photosynthetic rate measured at saturating light and CO₂ probably cannot be accounted for by an inhibition of the membrane-associated reactions. The damage to photosynthesis that occurs under conditions of high light and cold temperatures is even more severe than chilling temperatures alone, resulting in more than a 50% reduction in chloroplast activity after only 6 hours (5). The mechanism of injury may be completely different than that observed after chilling in the dark, or the increased damage may arise from additional injury incurred by high light at cold temperatures.