Photosynthesis in Species of Flaveria CO2 Compensation Concentration, O2 Influence on Photosynthetic Gas Exchange and δ13C Values in Species of Flaveria (Asteraceae)

10 out of the 21 known species of the genus Flaveria (Asteraceae), were included in a comparative study of the kinetic and regulatory properties of green leaf phosphoenolpyruvate (PEP) carboxylase. At least three kinetically distinct enzyme-forms were identified on the basis of their affinities for PEP and the degree of allosterism with respect to this substrate. The kinetic properties of PEP carboxylase of most of the species seemingly were modified in vivo depending on the growth conditions of the plants. K.(PEPf,,rjvalues of the enzyme from the five C3-C4 intermediate species ranged from 6 micromolar (F. chloraefolia, low light-grown) to 38 micromolar (F. pubescens, high light-grown). In contrast, the K,. for PEP of PEP carboxylase from the C3 species F. cronquistii (13 micromolar) apparently was not influenced by growth conditions. The response of the enzyme from the C3 and C3-C4 species was hyperbolic in all cases. A second isoform with a lower affinity for PEP (88-100 micromolar), but also hyperbolic kinetics was found in the C4 species F. brownii, whereas in the three other C4 species examined a PEP carboxylase with a still lower affinity for PEP (187-221 micromolar) and sigmoidal kinetics was present. These isozyme-related kinetic data were supported by analyses of the elution behavior of the enzyme during anion-exchange chromatography on DEAE-Trisacryl M. The results are discussed with respect to the evolution of C4 photosynthesis in the

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confidence: 77%

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confidence: 99%

Kinetic Properties of Phosphoenolpyruvate Carboxylase from C₃, C₄, and C₃-C₄ Intermediate Species of Flaveria (Asteraceae)

Bauwe¹,

Chollet²

1986

“…RESULTS AND DISCUSSION Previously published data on leaf anatomy, F, and 02 inhibition of net photosynthesis (1,12) have demonstrated that F. To determine the initial products of photosynthesis by the three Flaveria species, pulse-chase experiments with '4C02-'2C02 were performed on detached leaves. In the first experiment, the primary photosynthetic products labeled during the pulse in '4C02 were followed for up to 30 s in both the C4 species, F. trinervia, and the C3-C4 intermediate species, F. ramosissima (Fig.…”

Section: Methodsmentioning

confidence: 98%

“…Naturally occurring species with photosynthetic characteristics intermediate between C3 and C4 plants have been identified in the genera Mollugo (19), Panicum (4,14), Moricandia (2,9), Flaveria (1,10,12) and, most recently, Neurachne (Hattersley, personal communication). The intermediate nature of these species includes a Kranz-like leaf anatomy, a lower r2 (indicative of reduced photorespiration), and a reduced sensitivity of net photosynthesis to 02.…”

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confidence: 99%

Photosynthetic Characteristics of C₃-C₄ Intermediate Flaveria Species

Rumpho¹,

Ku²,

Cheng³

et al. 1984

“…Flaveria is a small genus in Asteraceae which contains C3, C4, and C3-C4 intermediate species (2,19,25). Several interspecific hybrids have been made both within and between photosynthetic types (1,4,9,15,25,28), but results from only one C3 X C4 hybrid have been reported (15) (the 'C3' species used in Ref.…”

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confidence: 99%

Enzymic and Photosynthetic Characteristics of Reciprocal F₁ Hybrids of Flaveria pringlei (C₃) and Flaveria brownii (C₄-Like Species)

Holaday¹,

Brown²,

Bartlett³

et al. 1988

The activities of key C4 enzymes in gel-filtered, whole-leaf extracts and the photosynthetic characteristics for reciprocal F, hybrids of Flaveria pringlei (C3) and F. brownii (C4-like species) were measured to determine whether any inherited C4-photosynthetic traits are responsible for their reduced CO2 compensation concentration values (AS Holaday, S Talkmitt, ME Doohan Plant Sci 41: 31-39). The activities of phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, and NADP-malic enzyme (ME) for the reciprocal hybrids are only about 7 to 17% of those for F. brownii, but are three-to fivefold greater than the activities for F. pringlei. The low activities of these enzymes in the hybrids appear to be the result of a partial dominance of F. pringlei genes over certain F. brownii genes. However, no such dominance occurs with respect to the expression of genes for NADP-malate dehydrogenase, which is as active in the hybrids as in F. brownii. In contrast to the situation with the enzymes above, cytoplasmic factors appear to determine the inheritance of NAD-ME. The NAD-ME activity in each hybrid is comparable to that in the respective maternal parent. Pulse-chase 14CO2 incorporation analyses at ambient CO2 levels indicate that the hybrids initially assimilate 7 to 9% of the total assimilated CO2 into C4 acids as compared to 3.5% for F. pringlei. In the hybrids, the percentage of 14C in malate decreases from an average of 6.5 to 2.1% after a 60-second chase in 12C02/air. However, this apparent C4-cycle activity is too limited or inefficient to substantially alter CO2 exchange from that in F. pringlei, since the values of net photosynthesis and 02 inhibition of photosynthesis are similar for the hybrids and F. pringlei. Also, the ratio of the internal to the external CO2 concentration and the initial slopes of the plot of CO2 concentration versus net photosynthesis are essentially the same for the hybrids and F. pringlei. At 45 micromoles CO2 per mole and 0.21 mole 02 per mole, the hybrids assimilate nearly fivefold more CO2 into C4 acids than does F. pringlei. Some turnover of the malate pool occurs in the hybrids, but the labelling of the photorespiratory metabolites, glycine and serine, is the same in these plants as it is in F. pringlei. Thus, although limited C4-acid metabolism may operate in the hybrids, we conclude that it is not effective in altering 02 inhibition of CO2 assimilation. The ability of the hybrids to assimilate more CO2 via phosphoenolpyruvate carboxylase at low levels of CO2 than does F. pringlei may result in an increased rate of reassimilation of photorespiratory CO2 and CO2 compensation concentrations below that of their C3 parent. If the hybrids do possess a limited C4 cycle, it must operate intracellularly. They are not likely to have inherited an intercellular compartmentation of C4 enzymes, since F. brownii has incomplete compartmentation of key C3 and C4 enzymes.