scholarly journals Oxaloacetate as the Source of Carbon Dioxide for Photosynthesis in Bundle Sheath Cells of the C4 Species Panicum maximum

1977 ◽  
Vol 60 (2) ◽  
pp. 193-196 ◽  
Author(s):  
Thomas B. Ray ◽  
Clanton C. Black
Keyword(s):  
Carbon Dioxide ◽  
Bundle Sheath ◽  
Panicum Maximum ◽  
C4 Species ◽  
Bundle Sheath Cells ◽  
Sheath Cells

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.

Aspartate Decarboxylation in Bundle Sheath Cells of Zea mays and Its Possible Contribution to C3 Photosynthesis

1981 ◽  
Vol 8 (2) ◽  
pp. 237 ◽  
Author(s):  
KSR Chapman ◽  
MD Hatch
Keyword(s):  
Zea Mays ◽  
Oxygen Evolution ◽  
Malic Enzyme ◽  
Bundle Sheath ◽  
Limited Capacity ◽  
C4 Species ◽  
Bundle Sheath Cells ◽  
C3 Photosynthesis ◽  
Mitochondrial Aspartate Aminotransferase ◽  
Sheath Cells

Strands of bundle sheath cells isolated from the NADP malic enzyme type C4 species, Zea mays, rapidly decarboxylate malate via NADP malic enzyme. The present studies show that these cells also decarboxylate aspartate, but at much lower rates. Aspartate decarboxylation is dependent upon added 2-oxoglutarate, is partially light dependent, and apparently proceeds via the following reaction sequence: aspartate ͛4 oxaloacetate ͛4 malate ͛4 pyruvate + CO2. Studies of the activity, properties, and location of enzymes indicated that these reactions are catalysed by a mitochondrial aspartate aminotransferase, mitochondrial or cytoplasmic NAD malate dehydrogenase, and chloroplast-located NADP malic enzyme, respectively. A mitochondria preparation isolated from Z. mays bundle sheath cells converted aspartate to oxaloacetate (with 2-oxoglutarate) and also pyruvate to alanine (with glutamate); the preparation did not reduce oxaloacetate to malate or decarboxylate malate at significant rates. Bundle sheath strands of Z. mays have a relatively limited capacity for HCO3- plus ribose 5-phosphate dependent oxygen evolution and rates were almost as high with aspartate plus 2-oxoglutarate. We suggest that amongst NADP malic enzyme type C4 species there may be a direct relationsip between the capacity of bundle sheath cells to decarboxylate aspartate and their potential for the photosystem II-mediated oxygen evolution.

Analysis of Bundle Sheath Conductance and C4 Photosynthesis using a PEP-Carboxylase Inhibitor

1997 ◽  
Vol 24 (4) ◽  
pp. 549 ◽  
Author(s):  
R. Harold Brown
Keyword(s):  
C4 Photosynthesis ◽  
Co2 Assimilation ◽  
Co2 Exchange ◽  
Bundle Sheath ◽  
Panicum Maximum ◽  
Panicum Miliaceum ◽  
Pep Carboxylase ◽  
C4 Species ◽  
Bundle Sheath Cells ◽  
Sorghum Bicolor L

High [CO2] in bundle sheath cells (BSC) allows high rates of CO2 assimilation (A) and minimises photorespiration in C4 leaves. The [CO2] in BSC is likely to be low when PEPcase is inhibited by 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP), but Rubisco is still functional. The degree of C4 photosynthesis can be assessed by decreased A and the conductance of BSC walls by the slope of A versus [CO2] during application of DCDP. Inhibition of A by 4.0 mM DCDP was 87-100% in C4 species and was overcome by increasing [CO2] to 2.0-2.5 kPa. In C3 -C4 species in Moricandia, Panicum and Neurachne, A and its inhibition by O2 were unchanged by DCDP, but in C3 -C4 and C4 -like species and interspecific hybrids of Flaveria, A was reduced and its inhibition by O2 was increased. Conductance of BSC walls was 1.13, 1.96, and 2.35 mmol m-2 s-1 in the C4 species, Sorghum bicolor (L.) Moench, Panicum miliaceum L., and Panicum maximum Jacq., respectively. There was no effect of O2 on A in DCDP-treated C4 leaves, apparently because the low conductance of BSC walls masks the influence of O2 on CO2 exchange in these cells.

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