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.

Effect of Growth Form, Salinity, Nutrient and Sulfide on Photosynthesis, Carbon Isotope Discrimination and Growth of Red Mangrove (Rhizophora mangle L.)

1992 ◽  
Vol 19 (5) ◽  
pp. 509 ◽  
Author(s):  
GH Lin ◽  
LDSL Sternberg
Keyword(s):  
Stomatal Conductance ◽  
Carbon Isotope ◽  
Carbon Isotope Discrimination ◽  
High Salinity ◽  
Co2 Assimilation ◽  
Transpiration Efficiency ◽  
Growth Forms ◽  
Growth Responses ◽  
Isotope Discrimination ◽  
Red Mangrove

The red mangrove (Rhizophora mangle L.), a dominant mangrove species in Florida, frequently occurs in two distinct growth forms, scrub and tall trees. These two growth forms show significant differences in physiology in the field, with lower CO2 assimilation rate, stomatal conductance, and carbon isotope discrimination or higher transpiration efficiency for the scrub form. To elucidate the possible factors responsible for these physiological differences, we studied the physiological and growth responses of scrub and tall red mangrove seedlings grown hydroponically in the greenhouse under 12 different growth conditions combining three salinities (100, 250, 500 mM NaCl), two nutrient levels (10, 100% strength of full nutrient solution), and two sulfide concentrations (0, 2.0 mM Na2S). The two growth forms showed similar physiological and growth responses to these treatments, suggesting no genetic control of physiological and growth differences between the growth forms of this species. High salinity, low nutrient level, and high sulfide concentration all significantly decreased CO2 assimilation, stomatal conductance, and plant growth, but only salinity significantly decreased intercellular CO2 concentration and leaf carbon isotope discrimination, suggesting that the lower carbon isotope discrimination, or higher transpiration efficiency, observed for scrub mangroves in the field is caused only by high salinity during the dry season. Hypersalinity thus seems to be one of the stressful environmental conditions common to all scrub red mangrove forests studied in southern Florida.

On the effect of heavy water (D2O) on carbon isotope fractionation in photosynthesis

2008 ◽  
Vol 35 (3) ◽  
pp. 201 ◽  
Author(s):  
Guillaume Tcherkez ◽  
Graham D. Farquhar
Keyword(s):  
Carbon Isotope ◽  
Heavy Water ◽  
Carbon Isotope Discrimination ◽  
Co2 Assimilation ◽  
Xanthium Strumarium ◽  
Phase Component ◽  
Isotope Discrimination ◽  
Internal Conductance ◽  
On Line ◽  
Co2 Addition

Internal conductance to carbon dioxide is a key aspect of leaf photosynthesis although is still not well understood. It is thought that it comprises two components, namely, a gas phase component (diffusion from intercellular spaces to cell walls) and a liquid phase component (dissolution, diffusion in water, hydration equilibrium). Here we use heavy water (D2O), which is known to slow down CO2 hydration by a factor of nearly three. Using 12C/13C stable isotope techniques and Xanthium strumarium L. leaves, we show that the on-line carbon isotope discrimination (Δ13C, or Δobs) associated with photosynthesis is not significantly decreased by heavy water, and that the internal conductance, estimated with relationships involving the deviation of Δ13C, decreased by 8–40% in 21% O2. It is concluded that in typical conditions, the CO2-hydration equilibrium does not exert an effect on CO2 assimilation larger than 9%. The carbon isotope discrimination associated with CO2 addition to ribulose-1,5,bisphosphate by Rubisco is slightly decreased by heavy water. This effect is proposed to originate from the use of solvent-derived proton/deuteron during the last step of the catalytic cycle of the enzyme (hydration/cleavage).

Partitioning of Carboxylase Activity in Nitrogen-Stressed Sugarcane and Its Relationship to Bundle Sheath Leakiness to CO2, Photosynthesis and Carbon Isotope Discrimination

1995 ◽  
Vol 22 (6) ◽  
pp. 903 ◽  
Author(s):  
SA Ranjith ◽  
FC Meinzer ◽  
MH Perry ◽  
M Thom
Keyword(s):  
Gas Exchange ◽  
Carbon Isotope ◽  
Carbon Isotope Discrimination ◽  
Leaf Gas Exchange ◽  
Bundle Sheath ◽  
Rubisco Activity ◽  
Carboxylase Activity ◽  
Isotope Discrimination ◽  
N Supply

We studied the effects of external nitrogen (N) supply on ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, phosphoenolpyruvate carboxylase (PEPC) activity, leaf gas exchange, carbon isotope discrimination (Δ), and bundle sheath leakiness to CO2 (Φ) in two cultivars of the C4 grass, sugarcane (Saccharum spp. hybrid). In addition to reducing overall levels of carboxylase activity and therefore photosynthetic rates, reduced N supply altered the partitioning of carboxylase activity. Under long-term N stress (4 months) Rubisco activity decreased more than PEPC activity causing significant reductions in the Rubisco/PEPC activity ratio, a measure of the ratio of C3 to C4 cycle activity. Concurrent determinations of Δ for leaf dry matter and the prevailing ratio of intercellular to ambient partial pressure of CO2 (pI/pa) during leaf gas exchange suggested that the decreased partitioning of N to Rubisco activity under long-term N stress led to increased Φ and reduced photosynthetic efficiency. The two cultivars studied maintained similar PEPC activities but differed genetically in regard to investment of N in Rubisco. Greater investment of N in Rubisco was associated with higher rates of photosynthesis and growth at similar or slightly lower leaf N content, indicating that greater relative investment of N in Rubisco activity also led to higher N-use efficiency. The results suggest that regulation of the ratio of C3 to C4 pathway activity and its consequences for Φ may play a key role in the photosynthetic performance and growth of C4 grasses under both favourable and stressful conditions.

Carbon isotope discrimination in leaf and stem sugars, water-use efficiency and mesophyll conductance during different developmental stages in rice subjected to drought

1998 ◽  
Vol 25 (4) ◽  
pp. 489 ◽  
Author(s):  
A. Scartazza ◽  
M. Lauteri ◽  
M.C. Guido ◽  
E. Brugnoli
Keyword(s):  
Water Use Efficiency ◽  
Carbon Isotope ◽  
Water Use ◽  
Carbon Isotope Discrimination ◽  
Developmental Stages ◽  
Grain Filling ◽  
Co2 Assimilation ◽  
Mesophyll Conductance ◽  
Isotope Discrimination ◽  
Use Efficiency

Carbon isotope discrimination (Δ), growth analysis, water-use efficiency (WUE) and gas exchange characteristics were studied in rice plants (Oryza sativa L.) subjected to drought during different developmental stages. Drought caused major effects on growth, WUE, Δ and photosynthetic CO2 assimilation. Substantial differences in the Δ of the bulk biomass among different organs and in carbohydrates extracted from leaves and stems were observed. Possible influences of chemical composition, fractionation during translocation and seasonal changes in the ratio of intercellular and atmospheric partial pressures of CO2 on such differences in Δ are discussed. Stem carbohydrate Δ was correlated with relative growth rate, and, during early grain filling, was negatively correlated with WUE measured between flowering and early grain filling. Δ in leaf sugars was used to estimate mesophyll conductance (gm), the conductance to CO2 diffusion inside leaves, from the intercellular air spaces to the chloroplast. During ontogeny, gm showed a marked progressive decrease, evident in both droughted plants and fully irrigated controls. There was a positive correlation between the rate of CO2 assimilation and gm. The analysis of Δ in leaf and stem carbohydrates is proposed as a useful indicator of growth, WUE and photosynthetic parameters relevant for yield of rice under drought-prone conditions.

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