Maintenance Carbon Cycle in Crassulacean Acid Metabolism Plant Leaves

Abstract

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

In situ studies of Crassulacean acid metabolism in several sympatric species of tropical trees of the genus Clusia

“…In CAM plants carbohydrate reserves accumulated during the light period are utilized during the dark period for the formation of PEP as a CO^-acceptor for fixation via PEP-C. For many CAM plants most of the carbon skeletons are the result of starch breakdown (Kenyon, Severson & Black, 1985). In Clusia soluble sugars and starch contributed to the formation of malate and citrate (Popp et al, 1987;Ball et aL, 1991), although rhe apparent contribution of starch is somewhat higher in our case.…”

Participation of citric acid and isocitric acid in the diurnal cycle of carboxylation and decarboxylation in the common ice plant

“…Also, earlier accumulation of citrate than malate during the induction of CAM was evidenced before by Herppich et al (1995). An increased isocitrate level was detected so far in leaves of obligate CAM species Kalanchöe daigremontiana and Tillandsia pohliana, and C 3 /CAM intermediate Sedum telephium (Kenyon et al 1985;Chen et al 2002;Freschi et al 2010). However, to our knowledge this is the first report on the nocturnal accumulation of isocitrate in response of salt stress in M. crystallinum.…”

CAM Photosynthesis in Bromeliads and Agaves: What Can We Learn from These Plants?

“…Although starch represents the main carbohydrate to provide PEP in many CAM plants, there are also CAM plants that show a smaller diel change in starch levels because they are also capable of storing carbohydrates in the form of hexose inside the vacuole [49], as observed in Ananas comosus (pineapple) [50,51]. Therefore, there are differences among CAM plants in their diel changes of energy-rich compounds used for nocturnal organic acid synthesis [52].…”