Temperature Dependence of Carbon Isotope Fractionation in CAM Plants

Abstract

ABSTRACrThe carbon isotope fractionation associated with nocturnal malic acid synthesis in Kalanchoe daigremontiana and Bryophyllum tubiflorum was calculated from the isotopic composition of carbon-4 of malic acid, after appropriate corrections. In the lowest temperature treatment (17°C nights, 23°C days), the isotope fractionation for both plants is -4%0(that is, malate is enriched in 13C relative to the atmosphere). For In the case of K. daigremontiana, the isotope fractionation associated with malate synthesis is independent of CO2 concentration. It appears that stomatal aperture decreases as CO2 concentration increases, and the ratio ofexternal CO2 concentration to internal CO2 concentration stays constant, as does the partitioning of the internal CO2 pool (9). Results obtained from isotopic studies have been correlated with results ofgas-exchange studies (7,20).It has been known for some time that nocturnal CO2 fixation contributes decreasingly to net CO2 fixation in CAM plants at higher temperatures (14,15,25). The purpose of this work is to learn about the temperature dependences of individual steps in the CAM pathway. Because our method focuses specifically on malate synthesis, we can learn about how rates of diffusion and carboxylation change as the temperature increases. We also present data concerning changes in the isotopic composition of malate during deacidification which tell about the mechanics of the deacidification process. MATERIALS AND METHODSPlants ofKalanchoe daigremontiana and Bryophyllum tubiflorum were grown from leaflets in a well-ventilated chamber in the University of Wisconsin Biotron with a 10-h light period and a 14-h dark period. The air in the Biotron circulates freely, with a complete turnover in 4 min; Its 6'3C value is -8%o. The plants were watered on alternate days with water and with half-strength Hoagland solution. Three temperature regimes were investigated: the first set of experiments was conducted with 5-month-old plants with a 17°C night temperature and a 23°C day temperature. After sample collection was complete, the temperature was changed to 22°C/28°C and the plants were allowed to adapt for 10 d before samples were taken. After samples were taken at the second temperature, the temperature was changed to 27°C/33°C and the plants were allowed to adapt for 10 d before samples were taken.

Anapleurotic CO2 Fixation by Phosphoenolpyruvate Carboxylase in C3 Plants

“…Initial studies focused on the distinction between C3 and C4 plants, but subsequent studies have revealed a wealth of detail with regard to relative rates of carboxylation, stomatal diffusion, CO2 hydration, and other steps (2,7,13). For (3,12) and an explanation in terms of the mechanism of fatty acid synthesis has been given (3).…”

“…Isotope ratio measurements were made on a Finnigan Delta-E isotope-ratio mass spectrometer and are given relative to the usual PDB standard (1). Combustions were conducted in sealed tubes (2) Figure 1.…”

Carbon Dioxide and Water Demand: Crassulacean Acid Metabolism (Cam), a Versatile Ecological Adaptation Exemplifying the Need for Integration in Ecophysiological Work

“…Depending to some extent on taxonomic distribution, NAD-and NADPdependent malic enzymes and NAD-malate dehydrogenase plus PEP carboxykinase bring about the decarboxylation of malic acid remobilized from the vacuoles (reviewed by Winter, 1985). Although Deleens, Treichel & O'Leary (1985) concluded from studies of carbon-isotope fractionation that malic acid efflux from the vacuole and not malate decarboxylation is the rate-limiting step in remobilization, some properties of NAD-malic enzyme described recently are interesting in relation to possible stabilization of the night-day shift. NAD-malic enzyme exists in at least three aggregational states: a dimer, a tetramer and an octomer.…”

Short-Term Measurement of Carbon Isotope Fractionation in Plants

“…The youngest fully expanded leaf was used for isotope fractionation studies. Kalanchoe daigremontiana was from the same clone used in previous studies in our laboratory (8). The eight youngest fully expanded leaves were used.…”

“…This isotopic information reflects the history of the plant during a short term and is more nearly independent of long-term influences. Studies have been made of the effect of temperature (8), CO2 concentration (12), and species (17) Soybean (Glycine max) was strain Mitchell. The two youngest triplets of fully expanded leaves were used in each experiment.…”