The Role of Light in the Induction of Nitrate Reductase Activity in Etiolated Shoots of Triticum Vulgare

Vinodh Ratnala²*, Dsvgk. Kaladhar¹ and B. Seshagiri²

²Department of Biochemistry, M.V.R College of Post-Graduate Studies, Visakhapatnam India.

¹Department of Biochemistry and Bioinformatics, GITAM University, Visakhapatnam India.

ABSTRACT: The etiolated shoots were exposed to a constant intensity of light (5000 lux supplied by a bank of white, cool, fluorescent lights) in the presence of optimal concentration of the substrate – inducer (20mM KNO3). When the etiolated shoots were exposed to light and 20mM KNO3 simultaneously, there was a progressive synthesis of photosynthetic pigments and induction of NR, assayed by the in vivo method under optimal assay conditions, with time of exposure (0,4,8,12, and 24 hours). The amount of Chl b synthesis, compared to that of Chl a, was less throughout the time of exposure to light. Chl a/b remained constant up to 8 hours of exposure to light and decreased slightly thereafter. A positive correlation was observed between the amount of total chlorophyll and the magnitude of in vivo NR activity throughout the 24 hours period. Significantly, by the 24th hour of greening, the amount of NR activity in the 3-day-old greening shoots was 1.75 micromole NO2 produced per hour per gram fresh weight, a value almost equal to that of 7-day-old green leaves induced under similar conditions. Etiolated shoots kept in darkness throughout the NR induction period did not show any enzyme activity, indicating that even in the presence of optimal external nitrate, the NR-inducer; light is still and perquisite for optimal induction of NR activity.

KEYWORDS: Etiolated Shoots; Photosynthetic Pigments; Substrate Inducer; Triticum Vulgare

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