Plant Physiol.
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Plant Physiology 68:722-726 (1981)
© 1981 American Society of Plant Biologists

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Articles

Ontogenetic Variation of Nitrogenase, Nitrate Reductase, and Glutamine Synthetase Activities in Oryza sativa1

Peter van Berkum2 and Charles Sloger

United States Department of Agriculture, Science and Education Administration, Agricultural Research, Room 116, Building 011-A, BARC-West, Beltsville, Maryland 20705, Cell Culture and Nitrogen Fixation Laboratory, Room 116, Building 011-A, BARC-West, Beltsville, Maryland 20705

The relationship between the rates of nitrogenase, nitrate reductase, and glutamine synthetase activities, and plant ontogeny in rice (Oryza sativa L.), cultivar `M9', grown in salt marsh sediment with and without nitrate treatment was studied. In both treatments, nitrogenase activity measured as the immediate linear rate of acetylene reduction by bacteria associated with the roots varied with plant age. In control plants, the nitrogenase activity developed during the vegetative stage, peaked during early reproductive growth and then declined. The application of 10 kilograms N per hectare as KNO3 once every 2 weeks delayed the development of and decreased the nitrogenase activity. The nitrogenase activity in both treatments developed as leaf nitrate reductase activity declined. The per cent nitrogen of roots was negatively correlated with the rates of acetylene reduction during the life cycles of control and nitrate-treated plants. This suggests that the concentration of combined nitrogen in the plants controlled the development and rate of root-associated nitrogenase activity. During reproductive growth, no nitrate reductase activity was detected in the roots from either treatment. In control plants, the patterns of nitrogenase activity and glutamine synthetase activity in the roots were similar. Thus, rice roots have the potential to assimilate ammonia while fixing N2. During the vegetative and early reproductive stages of growth, the development of maximal rates of nitrogenase activity coincided with an increase of total nitrogen of the plants in both treatments.

2 Supported by United States Department of Agriculture, Science and Education Administration, Agricultural Research, Cell Culture and Nitrogen Fixation Laboratory, Beltsville, MD, and the Agronomy Department, University of Maryland, College Park, MD, under Cooperative Agreement 12-14-1001-1387. Scientific Article A 2846, Contribution 5897 of the Maryland Agricultural Experiment Station, Department of Agronomy, College Park, MD 20742.

1 Supported by United States Department of Agriculture Competitive Grant 5901-0410-9-0254-0.






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Copyright © 1981 by the American Society of Plant Biologists