Malate Metabolism in the Dark After ¹³CO₂ Fixation in the Crassulacean Plant Kalanchoë tubiflora

Abstract

The metabolism of [13C] Many questions remain unanswered regarding the intracellular movement and metabolism of malate formed during dark periods in plants performing CAM (11,12,18). Of particular interest is the interaction between mitochondrial malate metabolism and the reactions associated with malate formation at night. In this regard, previous studies have revealed the following: (a) malate formed in the dark from isotopically labeled carbon dioxide is initially labeled in the 4-C position as a result of carboxylation of PEP3 by PEP carboxylase (17); (b) after some time in the dark, a proportion of the labeled carbon atoms also appear in the 1-C position of malate-by the end of the night, the proportion of 4-C to 1-C labeled malate generally approaches a ratio of about 2:1 (1); (c) only singly labeled (i.e. [4-'3C] In the present study, the CAM plant Kalanchoe tubiflora was labeled using 13C02 for short intervals during an entire dark cycle. By harvesting plants immediately after labeling and at the end of the dark period, information was obtained on the temporal pattern of mitochondrial malate fluxes, the respiration of malate, and the formation of malate from respired CO2 during the night.

Measurements of the Engagement of Cyanide-Resistant Respiration in the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana with the Use of On-Line Oxygen Isotope Discrimination

“…Earlier evidence that fumarase randomization and futile cycling of malate do not occur during deacidification (10,19) favors the view that only a small proportion of malate is oxidized in the mitochondria. Although previous (180/16O) exchange measurements (22) established high rates of 02 uptake in the light in CAM plants (about 50% of 02 evolution), these appear to be mediated by the Mehler reaction rather than by mitochondrial metabolism.…”

Malate. Jack of all trades or master of a few?

“…Due to space constraints we chose to focus on root exudation and stomatal function. However, there is also a wealth of important literature on its role in C4 and CAM metabolism as well as in fruit quality and development we refer the interested reader to (Kalt et al, 1990;Cushman and Bohnert, 1999;Brautigam et al, 2008;Carrari et al,2006;Hawker, 1969) for further details. To summarize our article we think it is fair to say that great advances have been made in understanding the control of, and by, malate in the last few years.…”

Carbon-Isotope Composition of Biochemical Fractions and the Regulation of Carbon Balance in Leaves of the C3-Crassulacean Acid Metabolism Intermediate Clusia minor L. Growing in Trinidad

“…Recycling of respiratory C o t was calculated as the difference between dawn and dusk changes in malic acid (LPdmal in mmol m-') and integrated nighttime coz uptake (Ad-dCOz in mmol m-') assuming that 1 mol of malic acid is synthesized for every 1 mol of COz fixed. This also assumes that a negligible amount of malate was respired directly at night to provide additional energy requirements for H+ accumulation (Kalt et al, 1990). Citric acid was not included in the calculations of recycling since the accumulation of citric acid at night is unlikely to result in net acquisition of Con (Lüttge, 1988;Ilaag-Kerwer et al, 11992).…”