ACTIVITY, STABILITY AND CHANGES DURING PLANT OEVELOPNENT IN NITRATE REDUCTASE OF WINGED BEAN [ Psophocarpus tetragonolobus (L.) DC] LEAVES
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Date
1987
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Mahatma Phule Krishi Vidyapeeth, Rahuri.
Abstract
Winged bean seedlings were grown in soil-filled pots
under ftfflfl&~ house conditions of the Department of Agricul
tural Chemistry and Soil Science, Flahatma Phule Agricultural
University, Rahuri, during the months from April to August
1986^ for standardizing in_ vivo assay conditions for
trifoliate leaf NR, Separate experiments were conducted
to study the influence of pre-incubation temperature (0°,
15° and 30°C) under dark conditions on iri vivo NR activity
and also to monitor the changes in NR activity during plant
development.
The in, vivo assays for trifoliate leaf NR wee opti
mized in respect of n-propanolt Triton-X-100 and substrate
concentration. It was noticed that 4 per cent (v/v) n
propanol with 0,05 per cent (v/v) Triton-X-100 was found to
be optimum for maximum in_ vivo NR activity. The optimum
nitrate concentration observed was 100 m*.. A linear rela
tionship between NR activity and reaction time was found
over a period of 2-hr, When leaf sections (squares) of uppermost just
expanded trifollates of winged bean were incubated at 0,
15 and 30°C under dark conditions, the loss of activity
was fastest at 30°C and slowest at 0°C. The loss of acti
vity was only 15-2 0 per cent at the end of 10 hr incubation
at 0°C while the loss was 50 and 80 per cent at 15 and 30°C, '* V~ \ o respectively. The half^(t^) of enzyme at 30 C, was found to be approximately 4 hr while it was 10 hr at 15°C.
Nitrate reductase activity profiles within leaf
canopy were established upto 45 days of growth period on
the 12th,»21st, 30th and 45th days of growth. From studies
with changes in NR activity during plant development, it
was noticed that the fully expanded uppermost leaves had
the higher nitrate reductase activity than the middle and
lower leaves. The uppermost just expanded leaves also had
higher NR activity during early growth stage and the acti
vity gradually declined with the advancement of the age of
the leaf.
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