Photosynthetic Metabolism and Activity of Carboxylating Enzymes in Emergent, Floating, and Submersed Leaves of Hydrophytes

Photosynthetic Metabolism and Activity of Carboxylating Enzymes in Emergent, Floating, and... Radioisotope techniques were used to compare photosynthetic CO2 fixation, activities of carboxylating enzymes, and the composition of photosynthates in 42 species of aquatic plants (emergent, floating, and submersed hydrophytes) collected from rivers Sysert' and Iset' in Sverdlovsk oblast (Russia). The submersed leaves, in comparison with the emergent and floating leaves, featured lower rates of potential photosynthesis (by 2.2 mg CO2/(dm2 h) on average), low content of the fraction I protein, and low activity of Rubisco and phosphoenolpyruvate carboxylase (PEPC). The averaged activities of Rubisco and PEPC were diminished in submersed leaves by 10 and 1 mg/(dm2 h), respectively. Different hydrophyte groups showed similar composition of assimilates accumulated after 5-min photosynthesis and did not differ in this respect from terrestrial plants. However, the incorporation of 14C into sucrose and starch in submersed leaves (30 and 9% of total labeling, respectively) was lower than in emergent and floating leaves (45 and 15%, respectively). At the same time, the incorporation of 14C into C4 acids (malate and aspartate) was 1.5 times higher in submersed leaves than in other leaf types. Analysis of leaf differentiation, the Rubisco/PEPC activity ratio, the PEPC activity, and the composition of primary photosynthates in the “pulse–chase” experiments revealed no evidence of the “C4 effect” in the submersed hydrophytes examined. The adaptation of hydatophytes to specific conditions of an aquatic environment was structurally manifested in the reduction (by a factor of 3–5) in the number of chloroplasts per 1 cm2 leaf area. This small number of chloroplasts was responsible for low photosynthetic rates in submersed leaves, although metabolic activities of individual chloroplasts were similar for all three hydrophyte groups. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Russian Journal of Plant Physiology Springer Journals

Photosynthetic Metabolism and Activity of Carboxylating Enzymes in Emergent, Floating, and Submersed Leaves of Hydrophytes

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Publisher
Springer Journals
Copyright
Copyright © 2003 by MAIK “Nauka/Interperiodica”
Subject
Life Sciences; Plant Sciences
ISSN
1021-4437
eISSN
1608-3407
D.O.I.
10.1023/A:1021936418052
Publisher site
See Article on Publisher Site

Abstract

Radioisotope techniques were used to compare photosynthetic CO2 fixation, activities of carboxylating enzymes, and the composition of photosynthates in 42 species of aquatic plants (emergent, floating, and submersed hydrophytes) collected from rivers Sysert' and Iset' in Sverdlovsk oblast (Russia). The submersed leaves, in comparison with the emergent and floating leaves, featured lower rates of potential photosynthesis (by 2.2 mg CO2/(dm2 h) on average), low content of the fraction I protein, and low activity of Rubisco and phosphoenolpyruvate carboxylase (PEPC). The averaged activities of Rubisco and PEPC were diminished in submersed leaves by 10 and 1 mg/(dm2 h), respectively. Different hydrophyte groups showed similar composition of assimilates accumulated after 5-min photosynthesis and did not differ in this respect from terrestrial plants. However, the incorporation of 14C into sucrose and starch in submersed leaves (30 and 9% of total labeling, respectively) was lower than in emergent and floating leaves (45 and 15%, respectively). At the same time, the incorporation of 14C into C4 acids (malate and aspartate) was 1.5 times higher in submersed leaves than in other leaf types. Analysis of leaf differentiation, the Rubisco/PEPC activity ratio, the PEPC activity, and the composition of primary photosynthates in the “pulse–chase” experiments revealed no evidence of the “C4 effect” in the submersed hydrophytes examined. The adaptation of hydatophytes to specific conditions of an aquatic environment was structurally manifested in the reduction (by a factor of 3–5) in the number of chloroplasts per 1 cm2 leaf area. This small number of chloroplasts was responsible for low photosynthetic rates in submersed leaves, although metabolic activities of individual chloroplasts were similar for all three hydrophyte groups.

Journal

Russian Journal of Plant PhysiologySpringer Journals

Published: Oct 17, 2004

References

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