This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by de Veau, E. J. Articles by van Berkum, P. Search for Related Content PubMed PubMed Citation Articles by de Veau, E. J. Articles by van Berkum, P. Agricola Articles by de Veau, E. J. Articles by van Berkum, P.

Metabolism and Enzymology

Photosynthesis and Photosynthate Partitioning in N₂-Fixing Soybeans

U.S. Department of Agriculture, Agricultural Research Service, BARC-West, Plant Photobiology Laboratory, Building 046A, Beltsville, Maryland 20705, Nitrogen Fixation and Soybean Genetics Laboratory, Building 011, Beltsville, Maryland 20705

Leaf area, chlorophyll content, net CO₂ photoassimilation, and the partitioning of fixed carbon between leaf sucrose and starch and soluble protein were examined in Glycine max (L) Merr. cv Williams grown under three different nitrogen regimes. One group (Nod+/+) was inoculated with Bradyrhizobium and watered daily with a nutrient solution containing 6 millimolar NH₄NO₃. A second set (Nod+/–) was inoculated and had N₂ fixation as its sole source of nitrogen. A third group (Nod^–) was not inoculated and was watered daily with a nutrient solution containing 6 millimolar NH₄NO₃. The mean net micromole CO₂ uptake per square decimeter per hour of the most recently matured source leaves was similar among the three groups of plants, being about 310. Mean leaf area of the source leaves, monitored for net photosynthesis was also similar. However, the mean milligram of chlorophyll per square decimeter of Nod+/– test leaves was about 50% lower than the other groups' leaves and indicated nitrogen deficiency. Thus, Nod+/– utilized their chlorophyll more efficiently for photosynthetic CO₂ uptake than the plants of the other treatments. The ratio of foliar carbohydrate:protein content was high in Nod+/– but low in the plants from the other two treatments. This inverse relationship between foliar protein and carbohydrate content suggests that more fixed carbon is diverted to the synthesis of protein when nitrogen availability is high. It was also found that Nod+/– sequestered more storage protein in their paraveinal mesophyll than plants of the other treatments. This study indicates that when inorganic nitrogen regimes are used to control photosynthate partitioning, then both leaf carbohydrate and leaf protein must be considered as end products of carbon assimilate allocation.