Malate Synthesis by Dark Carbon Dioxide Fixation in Leaves

Abstract

Te rates of dark CO2 fixation and the label distribution in malate following dark '4CO2 fixation in a C4 plant (maize), a C-3 plant (sunflower), and two Crassulacean acid metabolsm plants (BryopbyHum calycinum and KaIlancho diagrematianum leaves and plantiets) are compared. Within the first 30 minutes of dark 1"CO2 fixaton, leaves of maize, B. calycinum, and sunflower, and K. diagremondanum plantlets fix CO2 at rates of 1.4, 3.4, 0.23, and 1.0 Fmoles of C02/mg of chlkopbyfll hour, respectively. Net C02 fixathi stops within 3 hours in maize and sunflower, but Crassulaceans continue fixing CO2 for the duration of the 23-hour experiment.A bacterial procedure using Lactobacilus plantaum ATCC No. 8014 and one using malc enzyme to remove the P-carboxyl The characteristics of photosynthetic C02 fixation in C-3 and C4 plants have been extensively compared with Crassulacean acid metabolism (CAM) in recent years. In contrast, the relationship between dark C02 fixation in C-3 and C4 plants and the dark fixation in CAM plants has received little attention. In general, most investigations on dark C02 fixation have centered about CAM plants. In the characterization of CAM metabolism, rates of C02 uptake (3,4,22) and the label distribution in malate (5-7) have received much emphasis. Degradation of malate by Lctobacillusplantarum was first used by Utter (25) The purpose of this paper is to compare dark C02 fixation in a C-3 plant (sunflower), a C4 plant (maize), and two CAM plants (Kalanchoe diagremontianum and Bryophyllum calycinum) with respect to the rates of dark C02 fixation over a 23-hr period and the distribution of isotope in malate made during this period. In addition, dark C02 fixation in mature and immature (taken from plantlets) CAM leaves is compared. A preliminary report of this research has been published (17). MATERIALS AND METHODSPlant Material. K. diagremontianum and maize (Zea mays, var.Early Fortune) were grown in growth chambers with a regime of 12 hr light at 25 to 27 C followed by 12 hr dark at 18 to 20 C, under cool white fluorescent lamps supplemented with tungsten lamps. B. calycinum and sunflower (Helianthus annuus) were grown in the greenhouse under natural lighting. All plants were maintained on Hoagland solution (1 1).Dark "4CO2 Fixation. Dark C02 fixation was under green safelights. For 14CO2 fixation periods of less than 1 hr, sunflower leaves, Bryophyllum or Kalanchoe leaf discs (1-to 2-cm diameter), the youngest expanded leaf of maize seedlings or derooted Kalanchoe plantlets were tied together with sewing thread and floated on 10 ml of distilled H20 in 50-ml sealed flasks shaken in a water bath maintained at 25 C. Longer exposures (3 hr or more) to 14CO2 were performed in a darkroom at room temperature. '4C02 (5 ml, 2 IAmol/ml, 10 tCi/4tmol) was added by syringe through a serum cap which sealed the flask. The initial concentration of C02 in each flask was about 0.4%. "CO2 fixation was terminated by lifting the leaves by their threads and dropping them into boiling 80%o (v/v)

Dark Carbon Dioxide Fixation under Aerobic and Anaerobic Conditions in Maize Leaves after Preillumination in the Absence of Oxygen

“…"CO2 fixation. Moreover, the randomization rate via fumarase during the dark CO2 fixation in maize is very slow (18) and cannot explain our results.…”

Non‐photosynthetic Fixation of Carbon Dioxide and Possible Biological Roles in Higher Plants

“…In fact, there is now appreciable evidence that PEP carboxylase directs a significant proportion of the glycolytic carbon in the form of PEP towards OAA synthesis (Davies, 1979;ap Rees, 1980;Adams, Broman & Rinne, 1982). The evidence for the PEP branch-point is as follows: (i) The estimates of the rate of fixation of CO, by leaves of sunflower and maize in the dark gave values that are significant when compared to the rates of respiration (Levi, Perchorowicz & Gibbs, 1978). (ii) The estimates of the maximum catalytic activities of PEP carboxylase are comparable to the rate-limiting enzymes of glycolysis.…”

Pathway of Photosynthetic Malate Formation in Vitis vinifera, a C3 Plant

“…The data computed in Table III clearly identify the PCR sequence as the original source of the acceptor molecule in ,B-carboxylation, resulting ultimately in malate formation, because of very similar labeling patterns in PGA and C1,3 of malate. The somewhat high incidence of radioactivity in C-1 of malic acid must be attributed to some fumarase-catalyzed 14C interchange between carboxyl-carbon 1 and 4 of malate (20,26).…”