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Contribution of carbon fixed by Rubisco and PEPC to phloem export in the Crassulacean acid metabolism plant Kalanchoe daigremontiana.

Wild B, Wanek W, Postl W, Richter A - J. Exp. Bot. (2010)

Bottom Line: Three types of leaf carbon pools could be distinguished. (i) Starch and malate pools were dominant and showed a pattern of reciprocal mobilization and accumulation (85/54 and 13/48 mg C g(-1) DW, respective, at the beginning/end of phase I).The carbon isotope composition of these pools was compatible with predominant PEPC fixation (delta(13)C values of -13 and -11 per thousand for starch and malate compared to -11 per thousand of PEPC fixed carbon). (ii) Isotopic composition (-17 per thousand and -14 per thousand) and concentration of glucose and fructose (2 and 3 mg C g(-1) DW, respectively) were not affected by diurnal metabolism, suggesting a low turnover. (iii) Sucrose (1-3 mg C g(-1) DW), in contrast, exhibited large diurnal changes in delta(13)C values (from -17 per thousand in the evening to -12 per thousand in the morning), which were not matched by net changes in sucrose concentration.This suggests a high sucrose turnover, fed by nocturnal starch degradation and direct Rubisco fixation during the day.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Ecology and Ecosystem Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria. birgit.wild@univie.ac.at

ABSTRACT
Crassulacean acid metabolism (CAM) plants exhibit a complex interplay between CO(2) fixation by phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco), and carbon demand for CAM maintenance and growth. This study investigated the flux of carbon from PEPC and direct Rubisco fixation to different leaf carbon pools and to phloem sap over the diurnal cycle. Concentrations and carbon isotope compositions of starch, soluble sugars, and organic acids were determined in leaves and phloem exudates of Kalanchoë daigremontiana Hamet et Perr., and related to CO(2) fixation by PEPC and Rubisco. Three types of leaf carbon pools could be distinguished. (i) Starch and malate pools were dominant and showed a pattern of reciprocal mobilization and accumulation (85/54 and 13/48 mg C g(-1) DW, respective, at the beginning/end of phase I). The carbon isotope composition of these pools was compatible with predominant PEPC fixation (delta(13)C values of -13 and -11 per thousand for starch and malate compared to -11 per thousand of PEPC fixed carbon). (ii) Isotopic composition (-17 per thousand and -14 per thousand) and concentration of glucose and fructose (2 and 3 mg C g(-1) DW, respectively) were not affected by diurnal metabolism, suggesting a low turnover. (iii) Sucrose (1-3 mg C g(-1) DW), in contrast, exhibited large diurnal changes in delta(13)C values (from -17 per thousand in the evening to -12 per thousand in the morning), which were not matched by net changes in sucrose concentration. This suggests a high sucrose turnover, fed by nocturnal starch degradation and direct Rubisco fixation during the day. A detailed dissection of the carbon fixation and mobilization pattern in K. daigremontiana revealed that direct fixation of Rubisco during the light accounted for 30% of phloem sucrose, but only 15% of fixed carbon, indicating that carbon from direct Rubisco fixation was preferentially used for leaf export.

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Diurnal changes in the concentration (A) and δ13C (B) of sucrose (open symbols), fructose (closed symbols), and glucose (shaded symbols) of K. daigremontiana. CAM phases are denoted by dashed lines, the solid bar on the x-axis indicates the dark period. Data shown are the means ±SE of five replicate plants. At the end of the phases I, II, III, and IV, carbon from direct Rubisco fixation accounted for 7, 21, 19, and 54% of sucrose, respectively.
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fig4: Diurnal changes in the concentration (A) and δ13C (B) of sucrose (open symbols), fructose (closed symbols), and glucose (shaded symbols) of K. daigremontiana. CAM phases are denoted by dashed lines, the solid bar on the x-axis indicates the dark period. Data shown are the means ±SE of five replicate plants. At the end of the phases I, II, III, and IV, carbon from direct Rubisco fixation accounted for 7, 21, 19, and 54% of sucrose, respectively.

Mentions: Compound-specific stable isotope analysis with HPLC-IRMS revealed remarkable differences between diurnal patterns of soluble sugars in both concentration and isotopic composition. Glucose and fructose concentrations were highly correlated, both exhibiting non-significant decreases during the night and increases during the day. Sucrose, on the other hand, showed strong and highly significant changes in concentration (P <0.000001). Sucrose concentration started to increase in the morning and reached a maximum at the end of phase II, then decreased to the initial value at the end of phase III (Fig. 4).


Contribution of carbon fixed by Rubisco and PEPC to phloem export in the Crassulacean acid metabolism plant Kalanchoe daigremontiana.

Wild B, Wanek W, Postl W, Richter A - J. Exp. Bot. (2010)

Diurnal changes in the concentration (A) and δ13C (B) of sucrose (open symbols), fructose (closed symbols), and glucose (shaded symbols) of K. daigremontiana. CAM phases are denoted by dashed lines, the solid bar on the x-axis indicates the dark period. Data shown are the means ±SE of five replicate plants. At the end of the phases I, II, III, and IV, carbon from direct Rubisco fixation accounted for 7, 21, 19, and 54% of sucrose, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2837257&req=5

fig4: Diurnal changes in the concentration (A) and δ13C (B) of sucrose (open symbols), fructose (closed symbols), and glucose (shaded symbols) of K. daigremontiana. CAM phases are denoted by dashed lines, the solid bar on the x-axis indicates the dark period. Data shown are the means ±SE of five replicate plants. At the end of the phases I, II, III, and IV, carbon from direct Rubisco fixation accounted for 7, 21, 19, and 54% of sucrose, respectively.
Mentions: Compound-specific stable isotope analysis with HPLC-IRMS revealed remarkable differences between diurnal patterns of soluble sugars in both concentration and isotopic composition. Glucose and fructose concentrations were highly correlated, both exhibiting non-significant decreases during the night and increases during the day. Sucrose, on the other hand, showed strong and highly significant changes in concentration (P <0.000001). Sucrose concentration started to increase in the morning and reached a maximum at the end of phase II, then decreased to the initial value at the end of phase III (Fig. 4).

Bottom Line: Three types of leaf carbon pools could be distinguished. (i) Starch and malate pools were dominant and showed a pattern of reciprocal mobilization and accumulation (85/54 and 13/48 mg C g(-1) DW, respective, at the beginning/end of phase I).The carbon isotope composition of these pools was compatible with predominant PEPC fixation (delta(13)C values of -13 and -11 per thousand for starch and malate compared to -11 per thousand of PEPC fixed carbon). (ii) Isotopic composition (-17 per thousand and -14 per thousand) and concentration of glucose and fructose (2 and 3 mg C g(-1) DW, respectively) were not affected by diurnal metabolism, suggesting a low turnover. (iii) Sucrose (1-3 mg C g(-1) DW), in contrast, exhibited large diurnal changes in delta(13)C values (from -17 per thousand in the evening to -12 per thousand in the morning), which were not matched by net changes in sucrose concentration.This suggests a high sucrose turnover, fed by nocturnal starch degradation and direct Rubisco fixation during the day.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Ecology and Ecosystem Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria. birgit.wild@univie.ac.at

ABSTRACT
Crassulacean acid metabolism (CAM) plants exhibit a complex interplay between CO(2) fixation by phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco), and carbon demand for CAM maintenance and growth. This study investigated the flux of carbon from PEPC and direct Rubisco fixation to different leaf carbon pools and to phloem sap over the diurnal cycle. Concentrations and carbon isotope compositions of starch, soluble sugars, and organic acids were determined in leaves and phloem exudates of Kalanchoë daigremontiana Hamet et Perr., and related to CO(2) fixation by PEPC and Rubisco. Three types of leaf carbon pools could be distinguished. (i) Starch and malate pools were dominant and showed a pattern of reciprocal mobilization and accumulation (85/54 and 13/48 mg C g(-1) DW, respective, at the beginning/end of phase I). The carbon isotope composition of these pools was compatible with predominant PEPC fixation (delta(13)C values of -13 and -11 per thousand for starch and malate compared to -11 per thousand of PEPC fixed carbon). (ii) Isotopic composition (-17 per thousand and -14 per thousand) and concentration of glucose and fructose (2 and 3 mg C g(-1) DW, respectively) were not affected by diurnal metabolism, suggesting a low turnover. (iii) Sucrose (1-3 mg C g(-1) DW), in contrast, exhibited large diurnal changes in delta(13)C values (from -17 per thousand in the evening to -12 per thousand in the morning), which were not matched by net changes in sucrose concentration. This suggests a high sucrose turnover, fed by nocturnal starch degradation and direct Rubisco fixation during the day. A detailed dissection of the carbon fixation and mobilization pattern in K. daigremontiana revealed that direct fixation of Rubisco during the light accounted for 30% of phloem sucrose, but only 15% of fixed carbon, indicating that carbon from direct Rubisco fixation was preferentially used for leaf export.

Show MeSH
Related in: MedlinePlus