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Estimation of soil nitrogen, carbon and phosphorus:

Total nitrogen and carbon was estimated from soil sample by following methods of Vogel
(1961) and Black (1965) respectively. Available phosphorus was estimated by following

method of Jackson (1968).
Determination of soil moisture and pH:

Soil moisture and soil pH were determined by the methods of Kapur and Govil (2000) and
Jackson (1968) respectively.

Extraction of IAA, tryptophan and total phenol from root nodules and roots and their

estimation:
Mature, fresh root nodules and young roots are selected for the experiment. IAA was

extracted from fresh tissues of the plant. About 5 g each of roots and root nodules were taken

for extraction of IAA and purified by repeated thin layer chromatography (TLC) following
Sinha and Basu (1981) with slightly modification by Ghosh and Basu (2006) and was

estimated colorimetrically following Gordon and Weber (1951) using a standard curve
prepared from authentic IAA sample. Tryptophan was extracted from both root and root

nodules according to Nitsch (1955) and estimated colorimetrically following Hassan (1975).
The total phenol content was extracted and estimated from both the tissues after Bray and

Thorpe (1954).

Extraction and estimation of IAA-metabolizing and phenol-metabolizing enzyme:
IAA-oxidase from both root and root nodule was extracted and estimated following Sinha

and Basu (1981). Oxidation of IAA by peroxidase within both the tissues was estimated
following Kokkinakis and Brooks (1979) with modification by Datta and Basu (1998).

Peroxidase and polyphenol-oxidase were extracted from root and root nodule and estimated
according to Kar and Mishra (1976). The total protein content in the enzyme was estimated

following Lowry et al., 1951.

Statistical analyses were carried out following Panse and Sukhatme (1985) after taking three
replicates from each experiment.

RESULTS AND DISCUSSION

The plant Vigna radiata (L.) R. Wilczek produced plenty of root nodules after 60 days of
1
growth. Out of total number of nodules (both mature and immature) near about /4 of the
nodules were immature (Table 1) and the mature nodules were small, spherical to globose
and pinkish in colour.

Higher amount of IAA was detected and estimated within the mature root nodules of the
plant in comparison with young roots (Table 2). Within both the mature root nodules and the

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