Diurnal Changes in Metabolite Levels and Crassulacean Acid Metabolism in Kalanchoë daigremontiana Leaves.
Diurnal changes in levels of selected metabolites associated with glycolysis, the C(3) cycle, C(4)-organic acids, and storage carbohydrates were analyzed in active Kalanchoë daigremontiana Crassulacean acid metabolism leaves. Three metabolic transition periods occurred each day. During the first two hours of light, nearly all of the metabolite pools underwent transient changes. Beginning at daylight, stomata opened transiently and closed again within 30 minutes; malate synthesis continued for about 1 hour into the light; C(3) photosynthesis began within 30 minutes; and net quantities of starch and glucan began to accumulate after 2 hours, continuing linearly throughout the rest of the day.THE SECOND TRANSITION OCCURRED IN MIDAFTERNOON: stomata reopened; malate decarboxylation nearly terminated; and the assimilation of ambient CO(2) occurred primarily via the C(3) cycle. The third transition occurred at dark: stomata transiently closed before opening again; the C(3) cycle stopped; malate synthesis started in about 1 hour; starch and glucan degradation began within 1 hour; and the bulk of carbon flow was through glycolysis leading to the synthesis and accumulation of malate throughout the night. At night, the levels of metabolites involved in acidification and glycolysis (except for phosphoenolpyruvate) generally accumulated. Phosphoenolpyruvate levels peaked near midday and were minimal at night. The ribulose 1,5-bisphosphate pool was depleted at night, while sedoheptulose 1,7-bisphosphate, fructose 1,6-bisphosphate, glucose 6-phosphate, and fructose 6-phosphate accumulated.
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Botany Department, University of Georgia, Athens, Georgia 30602.
Holaday
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