Activity of Photosynthetic Enzymes in Leaves of Maize (Zea mays L.) Seedlings in Relation to Genotype and to Temperature Changes

Abstract

Summary Four inbred lines of flint maize (Zea mays L.) were grown at 24/22C (high) or 14/12 C (low) until the full expansion of the second leaf. At this date samples were taken of second leaves. Thereafter the temperature was changed from high to, low or from low to high. One, two and five days later samples were taken again. The leaves were assayed for the contents of chlorophyll and carotenoids and for the activities of PEP carboxylase, RuBP carboxylase, NADP-malic enzyme and NADP-malate dehydrogenase. After growth at low compared to high temperature, the genetic variability was considerably higher in all traits. Generally the following differences were caused by growth at low compared to high temperature: 1. a lower chlorophyll content; 2. a slightly higher carotenoid content; 3. a slightly higher PEP carboxylase activity; 4. a lower RuBP carboxylase activity; 5. no changes in NADP-malic enzyme activity; 6. no change in NADP-malate dehydrogenase activity in one line, a moderately reduced activity in a second line and an extremely reduced activity in two other lines. An exception was made by 270-1-1-7-1, which was chlorotic at low temperature and consequently had lower values for all traits. Transition from high to low temperature had the following effects: 1. a slight decrease in the chlorophyll content for about two, days; 2. an increase in the carotenoid content at once or after some days; 3. a slight increase in the PEP carboxylase activity with the exception of one line; 4. insignificant changes in RuBP carboxylase activity; 5. no changes in NADP-malic enzyme activity; 6. a sharp decrease in NADP-malate dehydrogenase activity in two lines after one day, but a temporary increase in the two other lines; 7. no severe retardation of shoot fresh weight accumulation. Transition from low to high temperature had the following effects: a fast and steady increase in the contents of 1. chlorophyll and 2. carotenoids; 3. a slight decrease in PEP carboxylase activity; 4. a fast and steady increase in RuBP carboxylase activity 5. no changes in NADP-malic enzyme activity; 6. a temporary decrease in NADP-malate dehydrogenase activity; 7. an interruption of shoot fresh weight accumulation for one to two days. The increase in the pigment content and the RuBP carboxylase activity was very slow in the chlorotic line. The implications of these results for the photosynthetic efficiency of maize at unfavorable temperature are discussed. Of the enzymes tested here, the RuBP carboxylase and the NADP-malate dehydrogenase could possibly be limiting this process in some genotypes at different situations of cool temperature.