Enzymes of carbohydrate and amino acid metabolism in developing and mature nodules of white clover

Abstract

The enzymic potential for the metabolism of carbohydrate (photosynthetic products) and amino acids (the assimilation of $NH4+$ was determined by enzyme assay and by immunodetection in developing and mature nodules of white clover. White nodules appeared within 6 d of placing stolon tip cuttings in wet sand. The protein content and enzyme activities of these young nodules increased by 10-fold within 9 d. The expression of leghaemoglobin and nitrogenase components 1 and 2 were just detectable in nodules at 7 d. All other enzymes measured were found in young roots and white nodules as well as in mature red nodules. However, the expression of sucrose synthase and glutamine synthetase (the key enzymes of sucrose metabolism and $NH4+$ assimilation, respectively) were greatly enhanced in nodules compared with roots. Nodule protein content, leghaemoglobin levels and enzyme activities peaked at approximately 50 d after taking stolon cuttings, and then declined by about 50% by 80 d. The results are discussed in the context of carbon and nitrogen fluxes in legume nodules.