scholarly journals Reduction of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase by Antisense RNA in the C4 Plant Flaveria bidentis Leads to Reduced Assimilation Rates and Increased Carbon Isotope Discrimination

1997 ◽  
Vol 113 (2) ◽  
pp. 469-477 ◽  
Author(s):  
S. von Caemmerer ◽  
A. Millgate ◽  
G. D. Farquhar ◽  
R. T. Furbank
Keyword(s):  
Carbon Isotope ◽  
Antisense Rna ◽  
Carbon Isotope Discrimination ◽  
C4 Plant ◽  
Bisphosphate Carboxylase ◽  
Isotope Discrimination ◽  
Flaveria Bidentis

Carbon Isotope Discrimination during C4 Photosynthesis: Insights from Transgenic Plants

1997 ◽  
Vol 24 (4) ◽  
pp. 487 ◽  
Author(s):  
Susanne von Caemmerer ◽  
Martha Ludwig ◽  
Anthony Millgate ◽  
Graham D. Farquhar ◽  
Dean Price ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Carbon Isotope Discrimination ◽  
Co2 Assimilation ◽  
Small Subunit ◽  
Bundle Sheath ◽  
Cauliflower Mosaic Virus ◽  
35S Promoter ◽  
Coding Region ◽  
Isotope Discrimination ◽  
Flaveria Bidentis

We have measured the discrimination against 13C during CO2 assimilation in Flaveria bidentis wild type plants and in transgenic Flaveria bidentis plants transformed (1) with an antisense RNA construct targeted to the nuclear encoded gene for the small subunit of Rubisco—these plants had reduced amounts of Rubisco, decreased CO2 assimilation rates and increased carbon isotope discrimination, which was also evident in the carbon isotope discrimination of leaf dry matter; and (2) transformed with the mature coding region of carbonic anhydrase, CA, from tobacco (Nicotiana tabacum) in the sense direction under the control of the cauliflower mosaic virus 35S promoter—these plants had slightly increased CA activity in the mesophyll as well as a 2–4-fold increase in CA activity in the bundle-sheath cells. The introduction of tobacco CA manifested itself by a reduction in CO2 assimilation rate and an increase in carbon isotope discrimination. We suggest that the increased carbon isotope discrimination is a result of increased bicarbonate leakage out of the bundle sheath.

Spatial Patterns of Carbon Isotope Discrimination and Allocation of Photosynthetic Activity in Sugarcane Leaves

1997 ◽  
Vol 24 (6) ◽  
pp. 769 ◽  
Author(s):  
Frederick C. Meinzer ◽  
Nicanor Z. Saliendra
Keyword(s):  
Carbon Isotope ◽  
Photosynthetic Activity ◽  
Carbon Isotope Discrimination ◽  
Incident Light ◽  
Water Soluble ◽  
C4 Plants ◽  
Leaf Base ◽  
Photosynthetic Gas Exchange ◽  
Bisphosphate Carboxylase ◽  
Isotope Discrimination

Longitudinal variation in carbon isotope discrimination (Δ), photosynthetic gas exchange, phosphoenolpyruvate carboxylase (PEPC) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities, chlorophyll and N content were characterised in the uppermost fully expanded leaf of sugarcane (Saccharum spp. hybrid) plants. Δ values of lamina tissue and the water-soluble fraction increased from the base to near the tip of the leaf then remained essentially constant, or declined along the rest of the leaf. Both the CO2 assimilation rate (A) and stomatal conductance (g) also increased from the base to the tip. The relative increase in A was much greater than that of g, causing the ratio of intercellular to ambient partial pressure of CO2 (pi/pa) to decrease substantially from leaf base to tip. Activities of both PEPC and Rubisco increased from leaf base to tip. Based on current models of factors determining Δ in C4 plants, the increase in Δ from the base to tip of sugarcane leaves appeared to be entirely attributable to decreasing pi/pa. Bundle sheath leakiness to CO2, the other major determinant of Δ in C4 plants, was nearly constant from the leaf base to tip, consistent with the nearly constant ratio of Rubisco and PEPC activity. Spatial allocations of carboxylase activity, chlorophyll, and N were highly correlated with prevailing levels of incident light at different points along the leaf. Partitioning of N and photosynthetic activity within individual leaves was consistent with allocation of N and photosynthetic capacity along vertical gradients of incident light reported for entire canopies.

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