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Diurnal Changes in Metabolite Levels and Crassulacean Acid Metabolism in Kalanchoë daigremontiana Leaves ¹

Botany Department, University of Georgia, Athens, Georgia 30602, Biochemistry Department, University of Georgia, Athens, Georgia 30602

Diurnal changes in levels of selected metabolites associated with glycolysis, the C₃ cycle, C₄-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; C₃ 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 CO₂ occurred primarily via the C₃ cycle. The third transition occurred at dark: stomata transiently closed before opening again; the C₃ 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.

¹ The research was supported in part by National Science Foundation Grant PCM 770-8548 and by the Mobile Foundation. This work was inspired by studying the quantitative determinations of organic acids and starch in CAM plants by H. B. Vickery and coworkers. The manuscript is presented in memory of H. B. Vickery's contributions to quantitative plant research.

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				L.-S. Chen, Q. Lin, and A. Nose A comparative study on diurnal changes in metabolite levels in the leaves of three crassulacean acid metabolism (CAM) species, Ananas comosus, Kalanchoe daigremontiana and K. pinnata J. Exp. Bot., February 1, 2002; 53(367): 341 - 350. [Abstract] [Full Text] [PDF]