Subdivision of C4-Pathway Species Based on Differing C4 Acid Decarboxylating Systems and Ultrastructural Features

A selection of C4 species was surveyed to determine the relationship between their content of C4 acid decarboxylating enzymes, the activities of several other enzymes implicated in the C4 pathway, and their anatomical and ultrastructural features. The species examined clearly fell into three groups according to whether they contained high levels of either NADP malic enzyme (EC 1.1.1.40), phosphoenolpyruvate carboxykinase (EC 4.1.1.49) or NAD malic enzyme (EC 1.1 .1.39). The occurrence of high NADP malic enzyme activity was always associated with higher NADP malate dehydrogenase activity, while those species distinguished by high activities of either of the other two decarboxylases invariably contained high aspartate aminotransferase and alanine amino- transferase activities. Each of these decarboxylating enzymes was located in bundle sheath cells. NAD malic enzyme, but not phosphoenolpyruvate carboxykinase, was associated with mitochondria. Light and electron micrographs revealed differences between these groups with respect to the intracellular location of chloroplasts and mitochondria in bundle sheath cells, and the content and ultrastructure of mitochondria. The trend was for species with high NAD malic enzyme to contain the most mitochondria in the bundle sheath cells with apparently the most extensively developed cristae membrane systems. However, mitochondrial respiratory enzyme activities were similar for the three groups of species. The basic similarities and differences between the three groups of C4 plants distinguished by their differing C4 acid decarboxylating systems are discussed, and schemes for the probable photosynthetic reactions in bundle sheath cells are presented. A nomenclature to distinguish between these groups is proposed.

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Mitochondrial Respiration in Relation to Photosynthetic C4 Acid Decarboxylation in C4 Species

Functional Plant Biology ◽

10.1071/pp9960001 ◽

1996 ◽

Vol 23 (1) ◽

pp. 1 ◽

Cited By ~ 16

Author(s):

A Agostino ◽

HW Heldt ◽

MD Hatch

Keyword(s):

Malic Enzyme ◽

Type Species ◽

Phosphoenolpyruvate Carboxykinase ◽

Alternative Oxidase ◽

Bundle Sheath ◽

C4 Species ◽

Bundle Sheath Cells ◽

A Minor ◽

Mitochondrial Malate Dehydrogenase ◽

Sheath Cells

Certain respiratory features of bundle sheath cells isolated from the C4 species Urochloa panicoides (phosphoenolpyruvate carboxykinase (PCK)-type)), Panicum miliaceum (NAD malic enzyme (NAD-ME)-type) and Zea mays (NADP malic enzyme (NADP-ME)-type) were examined in relation to the requirements of the C4 acid decarboxylation step of C4 photosynthesis. Cells from both PCK-type and NAD-ME-type species showed high rates of malate-dependent respiration; with ADP or uncoupler the rates were in the range 2-3 μatom O min-1 mg-1 chlorophyll, about 5-10-times the rates with other respiratory substrates. Studies with inhibitors of cytochrome oxidase and the alternative oxidase indicated negligible alternative oxidase-mediated malate respiration in cells from Z. mays, a minor contribution in U. panicoides cells, but possibly a major role for this oxidase in the respiration of P. miliaceum cells. These differences were related to the different roles of respiration in photosynthetic C4 acid decarboxylation. Oxaloacetate strongly suppressed malate-dependent respiration in P. miliaceum bundle sheath cells but not in U. panicoides cells. This difference in the response to oxaloacetate was not due to different kinetic features of the mitochondrial malate dehydrogenase but was apparently largely due to the much lower activity of the enzyme in U. panicoides bundle sheath mitochondria. We propose that insensitivity of respiration to oxaloacetate in bundle sheath cells of PCK-type species may be essential for maintaining the C4 acid decarboxylation process. The reverse may be true for NAD-ME- type species.

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Activity, Location and Role of NAD Malic Enzyme in Leaves With C4-Pathway Photosynthesis

Functional Plant Biology ◽

10.1071/pp9740357 ◽

1974 ◽

Vol 1 (3) ◽

pp. 357 ◽

Cited By ~ 46

Author(s):

MD Hatch ◽

T Kagawa

Keyword(s):

Malic Enzyme ◽

Phosphoenolpyruvate Carboxykinase ◽

Integral Function ◽

Bundle Sheath ◽

Leaf Extracts ◽

Acetyl Coa ◽

Mesophyll Cells ◽

C3 Species ◽

C4 Pathway ◽

Malic Enzyme Activity

C4 acid decarboxylation in many C4-pathway species is accounted for either by an NADP-specific malic enzyme or phosphoenolpyruvate carboxykinase but a major group lack these enzymes. The present paper provides evidence for the mediation of C4 acid decarboxylation in this group by an NAD malic enzyme located in bundle sheath mitochondria. This enzyme was most active with NAD and Mn2+ and, depending upon its source, activity was stimulated 5- to 15-fold by low con- centrations of CoA or acetyl-CoA. The activity in leaf extracts was 20-50 times that found in other groups of C4 species or in C3 species and was commensurate with the enzyme having an integral function in photosynthesis. For most species showing high NAD malic enzyme activity there was little activity when Mg2+ replaced Mn2+ and the low activity recorded with NADP was not activated by CoA or acetyl-CoA. In others there was an activator-dependent rate with NADP equivalent to 25-30% of the rate with NAD. Evidence for the location of the NAD malic enzyme in bundle sheath mitochondria is provided. On the basis of these and earlier studies a detailed scheme is proposed to account for decarboxylation of aspartate derived from mesophyll cells.

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Differential expression of C4 pathway genes in mesophyll and bundle sheath cells of greening maize leaves.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)60871-3 ◽

1987 ◽

Vol 262 (24) ◽

pp. 11726-11730 ◽

Cited By ~ 2

Author(s):

J Y Sheen ◽

L Bogorad

Keyword(s):

Differential Expression ◽

Bundle Sheath ◽

Bundle Sheath Cells ◽

Maize Leaves ◽

C4 Pathway ◽

Sheath Cells

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Photosynthesis in Gomphrena celosioides and Its Classification Amongst C4-pathway Plants

Functional Plant Biology ◽

10.1071/pp9760863 ◽

1976 ◽

Vol 3 (6) ◽

pp. 863 ◽

Cited By ~ 5

Author(s):

E Repo ◽

MD Hatch

Keyword(s):

Malate Dehydrogenase ◽

Malic Enzyme ◽

Bundle Sheath ◽

Mesophyll Cells ◽

C4 Species ◽

Bundle Sheath Cells ◽

Major Route ◽

Gomphrena Celosioides ◽

A Minor ◽

Sheath Cells

Monocotyledonous C4 species classified as NADP-ME-type transfer malate from mesophyll to bundle sheath cells where this acid is decarboxylated via NADP malic enzyme (EC 1.1.1.40) to yield pyruvate and CO2. The dicotyledon G. celosioides is most appropriately classified in thls group on the basis of high leaf activities of NADP malic enzyme and NADP malate dehydrogenase (EC 1.1.1.82). However, this species contains high aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2) activities and centripetally located bundle sheath chloroplasts, features more typical of other groups of C4 species that cycle aspartate and alanine between mesophyll and bundle sheath cells. During the present study, we found that these aminotransferases and NADP malate dehydrogenase were predominantly located in mesophyll cells, that malate was the major C4 acid labelled when leaves were exposed to 14CO2, and that label was initially lost most rapidly from the C-4 of malate during a chase in 12CO2. These results are consistent with the major route of photosynthetic metabolism being the same as that operative in other NADP-ME-type species, although this may be supplemented by a minor route utilizing aspartate. In contrast to monocotyledonous NADP-ME-type C4 species, isolated bundle sheath cells from G. celosioides were capable of rapid photoreduction of NADP as judged by products formed during assimilation of 14CO2 and their capacity for light-dependent oxygen evolution. This was related to a relatively high frequency of single unstacked granum in the chloroplasts of these cells.

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