Preferential C4-dicarboxylic acid synthesis, the postillumination CO2 burst, carboxyl transfer step, and grana configurations in plants with C4-photosynthesis

1970 ◽  
Vol 48 (10) ◽  
pp. 1795-1800 ◽  
Author(s):  
W. J. S. Downton
Keyword(s):  
Malic Enzyme ◽  
Calvin Cycle ◽  
Reducing Power ◽  
Acid Synthesis ◽  
Bundle Sheath ◽  
Short Term ◽  
Transfer Step ◽  
Malate Transport ◽  
Malic Enzyme Activity ◽  
Sheath Cells

An oxygen-insensitive postillumination CO2 burst occurs in many plants with the C4-pathway of photosynthesis. C4-species with a postillumination burst synthesize mainly aspartate during very short term photosynthesis and have low levels of 'malic' enzyme (EC. 1.1.1.40) activity. It is postulated that the burst is CO2 which normally participates in the carboxyl transfer step of C4-photosynthesis. The burst is absent in C4-species that produce mainly malate in short-term photosynthesis. This group of plants has very high 'malic' enzyme activity. Transport of malate to the bundle sheath layer and its metabolism by 'malic' enzyme provides reducing power (NADPH2) as well as CO2 to the Calvin cycle. This combination of products may attenuate the postillumination burst. Some malate formers show extreme grana reduction in bundle sheath chloroplasts which, is associated with a low capacity for generating reducing power. Malate transport compensates for this lack of reducing power in sheath cells with agranal chloroplasts. Transport of aspartate or oxaloacetate to the sheath cells does not transfer reducing power. The sheath chloroplasts of aspartate formers have well-developed grana but some reduction in grana within mesophyll chloroplasts is apparent in certain species. This reduction may reflect a low demand for reducing power where the major C4-acid synthesized is aspartate rather than malate.

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

1975 ◽  
Vol 2 (2) ◽  
pp. 111 ◽  
Author(s):  
MD Hatch ◽  
T Kagawa ◽  
S Craig
Keyword(s):  
Malic Enzyme ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Bundle Sheath ◽  
Intracellular Location ◽  
Bundle Sheath Cells ◽  
C4 Pathway ◽  
Malic Enzyme Activity ◽  
Mitochondrial Respiratory Enzyme ◽  
The Relationship ◽  
Sheath Cells

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.

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

1976 ◽  
Vol 3 (6) ◽  
pp. 863 ◽  
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.

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

1996 ◽  
Vol 23 (1) ◽  
pp. 1 ◽  
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.

Differential accumulation of plastid transcripts encoding photosystem II components in the mesophyll and bundle-sheath cells of monocotyledonous NADP-malic enzyme-type C4 plants

Planta ◽  
1991 ◽  
Vol 184 (3) ◽  
Author(s):  
Peter Westhoff ◽  
Karin Offermann-Steinhard ◽  
Michael H�fer ◽  
Kenneth Eskins ◽  
Angela Oswald ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Malic Enzyme ◽  
Bundle Sheath ◽  
C4 Plants ◽  
Bundle Sheath Cells ◽  
Sheath Cells
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