Sukumar R. Chatterjee

Nutritional potential ofVigna minima (Roxb.) Ohwi and Ohashi

The seed protein content and amino acid composition of 14 natural populations and their three-generation progenies (grown in different locations) belonging toVigna minima (Roxb.) Ohwi & Ohashi and ofV. umbellata cv IC 1568 have been investigated. The populations ofV. minima were sampled from different ecozones of Western Ghats of Kerala and Tamil Nadu (India). The range of variation in protein levels is narrow, but the protein content of the coastal population is higher than the rice bean suggesting its breeding potential for high protein and salt tolerant lines of rice bean. Although the seed protein content shows genotype × environment interaction, there is a substantial genetic variability among the populations. The tenuous relationship between protein content and yield conponents suggest the presence of correlation breakers which can be utilized in breeding programmes of rice bean. There is a broad genetic base in the levels of essential amino acids, and the range of variation observed is higher than that recorded for different species ofVigna andPhaseolus. The wild relative is nutritionally as good as or superior to the cultigen.

Nutritional potential of Vigna minima (Roxb.) Ohwi and Ohashi : II. Seed protein fractions and their amino acid composition

Quantitative variation in different fractions of seed proteins and their amino acid levels in populations ofVigna minima (Roxb.) Ohwi and Ohashi and inV. umbellata cv. IC 1568 — the rice bean — were investigated. Globulin I fraction, together with globulin II, constitutes 38 to 54 per cent of the total seed protein. The alkali soluble (glutelin) fraction is the second largest fraction. Both these fractions show broad range of variation, suggesting a broad genetic base. The profiles are population specific; the coastal population, which contains higher seed protein also possesses maximum levels of globulin I and glutelin fraction suggesting its potentiality for breeding lines with high protein content, high nutritive value, and salt tolerance. Protein content is positively correlated with globulin I and glutelin fractions, which are in turn positively correlated with each other. The amino acid profiles are specific not only to the fractions but also to the populations. The range of variation in the levels of all amino acids in different fractions is broad suggesting substantial genetic diversity. The average levels of lysine and sulphur amino acids are high in globulin I and glutelin fractions.Comparaison des variations quantitatives et qualitatives des differentes fractions obtenues a partir des graines de Vigna minima et V. umbellata

Light-mediated Regulation of Nitrate Reductase in Higher plants

Regulation of nitrate reductase (NR) by light is a complex process and is manifested through gene expression, both at the level of transcription and translation, covalent modification of the enzyme and supply of reductant. Light induces nia gene transcription by some still unknown mechanism. Light induction of nia mRNA is also mediated via phytochrome. By using protein synthesis inhibitors it has been observed that light enhances translation of NR mRNA. Light induction of NR synthesis follows the circadian rhythmicity. Cytokinin increases NR activity by regulating NR expression at the transcriptional level. In response to light-dark transition, NR is quickly inactivated/activated by phosphorylation/dephosphorylation. Inactivation of NR involves phosphorylation of the serine-543, located at the hinge 1 region connecting MoCo domain and cyt b domain of NR, by a Mg2+ dependent protein kinase and subsequent binding of an inhibitor protein. A type 2A protein phosphatase dephosphorylates/activates NR in response to light signal. Light also regulates supply of reductant via photosynthesis for activity of NR. Whether light is absolutely necessary for NR activity is also discussed.

Sunflower Nitrate Reductase: Purification and Characterization

A single isoform, NADH: nitrate reductase (NR), was purified 500 folds from sunflower leaves by affinity chromatography on Blue Sepharose CL-6B. Purified NR had a pH optima of 7.25 and a molecular weight of 210 kD. In SDS-PAGE, two bands of 47 and 56 kD were obtained. NADH: ferric citrate reductase activity was copurified with NR with a specific activity of 2. The Vmax of NADH: ferric citrate reductase was 8.69 units mg-1 protein and the apparent Km for ferric citrate was 0.435 mM.