Effect of Nitrate in the Rooting Medium on Carbohydrate Composition of Soybean Nodules

Abstract

Nodulated soybean plants (Glycine max IL.I Merr) were grown in sand culture. Carbohydrate composition of nodules, roots, and leaf blades was determined and related to the effects of nitrate in nutrient solution on nodule growth and on nitrogenase activity of nodules. When plants were grown without nitrate for 6 weeks and then supplied with 150 milligrams NO3-N/liter for 4 or 7 days, there was an 80% decline in acetylene reduction activity of nodulated roots, relative to the O-N control. The 80% decline in nitrogenase activity was accompanied by a decline in nodule glucose concentration of about 0.15 milligram per gram fresh weight and an increase in nodule sucrose concentration of about 0.23 milligram per gram fresh weight. Plants were grown with 0, 30, or 100 milligrams N03-N/liter for 5 or 6 weeks to study long-term effects of nitrate on nodule growth. The 100-N treatment reduced nodule weight/plant by 70% but reduced the sum of sucrose + glucose + fructose concentration in nodules by only 12%. The ratios of Isucrosel in nodules/Isucrosel in roots and Ifructosel in nodules/