The reciprocal relationship between diurnal changes in organic acid and storage carbohydrate was examined in the leaves of three Crassulacean acid metabolism plants. between pools of malate at night and carbohydrate in the day (2,15,16).In all CAM species studied, malate is the predominant organic acid that accumulates in CAM leaf tissue at night and is depleted during the day. Nocturnal '4C02 assimilation profiles indicate that various metabolites are labeled, especially aspartate, alanine, and intermediates ofthe citric acid cycle (17, 23). The percentage of the label that accumulates in these components relative to malate, however, is low. In some species, citrate fluctuates diurnally but the amplitude is three orders of magnitude less than that exhibited by malate (10,15,20,25