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.

scholarly journals Measurement of the Leakage of CO2 from Bundle-Sheath Cells of Leaves during C4 Photosynthesis

1995 ◽  
Vol 108 (1) ◽  
pp. 173-181 ◽  
Author(s):  
M. D. Hatch ◽  
A. Agostino ◽  
CLD. Jenkins
Keyword(s):  
C4 Photosynthesis ◽  
Bundle Sheath ◽  
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.

scholarly journals Overexpression of the chloroplastic 2-oxoglutarate/malate transporter disturbs carbon and nitrogen homeostasis in rice

2020 ◽  
Author(s):  
Shirin Zamani-Nour ◽  
Hsiang-Chun Lin ◽  
Berkley J Walker ◽  
Tabea Mettler-Altmann ◽  
Roxana Khoshravesh ◽  
...  
Keyword(s):  
C4 Photosynthesis ◽  
Tricarboxylic Acid Cycle ◽  
Carbon Assimilation ◽  
Amino Acid Content ◽  
Glutamate Synthase ◽  
Co2 Assimilation ◽  
Bundle Sheath Cells ◽  
Redox Poise ◽  
High Level ◽  
Malate Transporter

Abstract The chloroplastic 2-oxaloacetate (OAA)/malate transporter (OMT1 or DiT1) takes part in the malate valve that protects chloroplasts from excessive redox poise through export of malate and import of OAA. Together with the glutamate/malate transporter (DCT1 or DiT2), it connects carbon with nitrogen assimilation, by providing 2-oxoglutarate for the GS/GOGAT (glutamine synthetase/glutamate synthase) reaction and exporting glutamate to the cytoplasm. OMT1 further plays a prominent role in C4 photosynthesis: OAA resulting from phosphoenolpyruvate carboxylation is imported into the chloroplast, reduced to malate by plastidic NADP-malate dehydrogenase, and then exported for transport to bundle sheath cells. Both transport steps are catalyzed by OMT1, at the rate of net carbon assimilation. To engineer C4 photosynthesis into C3 crops, OMT1 must be expressed in high amounts on top of core C4 metabolic enzymes. We report here high-level expression of ZmOMT1 from maize in rice (Oryza sativa ssp. indica IR64). Increased activity of the transporter in transgenic rice was confirmed by reconstitution of transporter activity into proteoliposomes. Unexpectedly, overexpression of ZmOMT1 in rice negatively affected growth, CO2 assimilation rate, total free amino acid content, tricarboxylic acid cycle metabolites, as well as sucrose and starch contents. Accumulation of high amounts of aspartate and the impaired growth phenotype of OMT1 rice lines could be suppressed by simultaneous overexpression of ZmDiT2. Implications for engineering C4 rice are discussed.

scholarly journals Improving Light Use Efficiency in C4 Plants by Increasing Electron Transport Rate

Proceedings ◽  
2020 ◽  
Vol 36 (1) ◽  
pp. 203
Author(s):  
Maria Ermakova ◽  
Robert T. Furbank ◽  
Susanne von Caemmerer
Keyword(s):  
Electron Transport ◽  
Conversion Efficiency ◽  
C4 Photosynthesis ◽  
Foxtail Millet ◽  
Bundle Sheath ◽  
C4 Plants ◽  
Crop Species ◽  
Bundle Sheath Cells ◽  
Light Conversion Efficiency ◽  
Sheath Cells

C4 plants play a key role in world agriculture and strategies to manipulate and enhance C4 photosynthesis have the potential for major agricultural impacts. The C4 photosynthetic pathway is a biochemical CO2 concentrating mechanism that requires the coordinated functioning of mesophyll and bundle sheath cells of leaves. Chloroplast electron transport in C4 plants is shared between the two cell types; it provides resources for CO2 fixation therefore underpinning the efficiency of photosynthesis. Using the model monocot C4 species Setaria viridis (green foxtail millet) we demonstrated that the Cytochrome (Cyt) b6f complex regulates the electron transport capacity and thus the rate of CO2 assimilation at high light and saturating CO2. Overexpression of the Cyt b6f in both mesophyll and bundle sheath cells results in a higher electron throughput and allows better light conversion efficiency in both photosystems. Importantly, increased Cyt b6f abundance in leaves provides higher rates of C4 photosynthesis without marked changes in Rubisco or chlorophyll content. Our results demonstrate that increasing the rate of electron transport is a viable strategy for improving the light conversion efficiency in C4 crop species like maize and sorghum.

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