US EPA

4332829 

Journal Article 

Carbohydrate status and sucrose metabolism in mungbean roots and nodules 

Chopra, J; Kaur, N; Gupta, AK 

1998 

1 

Phytochemistry
ISSN: 0031-9422
EISSN: 1873-3700 

49 

7 

1891-1895 

WOS:000077640800008 

The activities of acid invertase, alkaline invertase and sucrose synthase (cleavage) were measured in roots and nodules of mungbean at different stages of development. High activities of these enzymes were observed at 30 and 50 days after sowing in nodules. Compared with other sucrose metabolising enzymes, alkaline invertase activity was highest in nodules at all stages of development. Activity of sucrose metabolizing enzymes in roots was significantly less than that observed in the nodules. Most of the sucrose appears to be transported as such through the roots to the nodules. Sucrose was the dominant free sugar and the concentration of glucose was higher than that of fructose at all stages of nodule development. Alkaline invertase from nodules was purified to electrophoretic homogeneity by ammonium sulphate fractionation, DEAL cellulose chromatography and Sephadex G-150 chromatography. The enzyme showed a sharp pH optimum at pH 7.0-7.5, optimum temperature of 40 degrees,K-m of 3-4 mM for sucrose, non-competitive inhibition by HgCl2 (K-i, 40 mu M) and had an M-r of approximately 355 000. Compared with raffinose and stachyose, sucrose was the better substrate for alkaline invertase. Energy of activation of alkaline invertase with different substrates was in the order, stachyose > raffinose > sucrose. The enzyme was unable to hydrolyse maltose and p-nitrophenyl-alpha-D-glucopyranoside, showing its true beta-fructosidase nature. Because of its low K-m, low energy of activation with near saturated substrate environment in nodules, alkaline invertase appeared better placed physiologically for sucrose cleavage. (C) 1998 Elsevier Science Ltd. All rights reserved. 

Vigna radiata; Leguminosae; mungbean; nodule; root; sucrose metabolism; sucrose synthase; invertase