Plant Physiology 67:335-340 (1981)
© 1981 American Society of Plant Biologists
Articles
Induction of Reduced Photorespiratory Activity in Submersed and Amphibious Aquatic Macrophytes 1
Michael E. Salvucci and
George Bowes
Department of Botany, University of Florida, Gainesville, Florida 32611
Incubation under water in a 30 C/14-hour or 12 C/10-hour photoperiod caused the CO2 compensation points of 10 aquatic macrophytes to decrease below 25 or increase above 50 microliters CO2 per liter, respectively. Submerged and aerial leaves of two amphibious angiosperms (Myriophyllum brasiliense and Proserpinaca palustris) maintained high compensation points when incubated in air but, when the submerged or aerial leaves of Proserpinaca were incubated under water, the compensation points dropped as low as 10. This suggests that, in addition to temperature and photoperiod, some factor associated with submergence regulates the compensation point of aquatic plants. In the high-compensation point plants, photorespiration, as a percentage of net photosynthesis, was equivalent to that in terrestrial C3 plants. For Hydrilla verticillata, the decreasing CO2 compensation points (110, 40, and 10) were associated with reduced photorespiration, as indicated by decreased O2 inhibition, decreased rates of CO2 evolution into CO2-free air, and increased net photosynthetic rates.
The decrease in the CO2 compensation points of Hydrilla, Egeria densa, and Cabomba caroliniana was accompanied by an increase in the activity of phosphoenolpyruvate, but not of ribulose bisphosphate, carboxylase. In Hydrilla, several C4 enzymes also increased in activity to the following levels (micromoles per gram fresh weight per hour): pyruvate Pi dikinase (35), pyrophosphatase (716), adenylate kinase (525), NAD and NADP malate dehydrogenase (6565 and 30), NAD and NADP malic enzymes (239 and 44), and aspartate and alanine aminotransferases (357 and 85), whereas glycolate oxidase (6) and phosphoglycolate and phosphoglycerate phosphatases (76 and 32) showed no change. Glycolate dehydrogenase and phosphoenolpyruvate carboxykinase were undetectable. The reduced photorespiration in these plants may be due to increased CO2 fixation via a C4 acid pathway. However, for three Myriophyllum species, some other mechanism appears operative, as phosphoenolpyruvate carboxylase was not increased in the low compensation point state, and ribulose bisphosphate carboxylase remained the predominant carboxylation enzyme.
1 This research was supported by Grant 5901-0410-8-0082-0 from the Competitive Research Grants Office of the United States Department of Agriculture-the Science and Education Administration and by Grant 249-K17 from the Bureau of Aquatic Plant Research and Control, Florida Department of Natural Resources. This is Florida Agricultural Experiment Station Journal Series No. 2459.
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