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|Authors:||Parve, Yogeshwarnand M|
Shinde, Dr. P.B
|Title:||INVESTIGATIONS ON NITRATE REDUCTASE IN TRIFOLIATE LEAVES AND INFLUENCE OF LEVELS OF BORON AND NITROGEN AND THEIR COMBINATIONS ON LEAF AND NODULE NITRATE REDUCTASE ACTIVITY, NODULATION AND LEGHAEMOGLOBIN CONTENT IN SOYBEAN|
|Publisher:||Mahatma Phule Krishi Vidyapeeth, Rahuri - 413 722|
|Abstract:||The present investigation was carried out to standardize the in vivo assay of nitrate reductase (NR) in trifoliate leaves of 20-day-old plants of soybean, cv. MACS- 124 and also to evaluate the influence of N and B and their combinations on NR activity in trifoliate leaves and nodules, nodule number, fresh weight of nodules and leghaemoglobin contents. A pot culture experiment was laid out in factorial randomised block design with three replications. The twelve treatment combinations of nitrogen (0, 500, 1000, 1500 mg urea) and boron (0, 50 and 100 mg borax) were applied before sowing in pots each filled with 10 kg soil. The soybean seedlings were grown in these pots under wire house conditions XIV Abstract contd... Parve Y.M. in natural day light during the months-February to May, 1997 at the Department of Biochemistry, Mahatma Phule Krishi Vidyapeeth, Rahuri. A substrate concentration of 100 mM was found to be optimum for maximal in vivo NR activity in soybean trifoliate leaves. Ar» inclusion of 3 % (v/v) n-propanol concentration in the infiltration media appeared to be optimum for aximum in vivo NR activity in trifoliate leaves. However, 1 % (v/v) npropanol with 0.05 % (v/v) Triton-X-100 in the infiltration media further improved N02~ formation and hence NR activity. A linear relationship was found between NR activity and leaf tissue weight (50-200 mg) . The highest NR activity was found in the third trifoliates than second and first trifoliates and cotyledonary leaves of one-month-old plants. The average NR activity which was low in the morning at 8.00 hr, increased during the first few hours of the photoperiod and continued to rise rapidly upto 14.00 hr. The NR activity, however, declined thereafter during the afternoon hours, i.e., at 17.00 hr. The highest nitrate reducing capacity was observed in trifoliate leaves as compared to other plant parts such as petioles, stems and roots of one-month-old plants. A significant increase in leaf and nodule NR activities was noticed with increasing evels of boron and XV Abstract contd... Parve Y.M. nitrogen. The maximum leaf and nodule NR activities were observed for a combination of 1500 mg urea and 100 mg borax 10 kg-1 of experimental soil pplied before sowing. The maximum NR activity was observed in plants receiving higher doses of nitrogen hich may be due to higher mobilization of nitrate in the leaves and nodules. The increased levels of boron probably increased NR activity via the metabolism of nucleic acids and proteins and energy turnover. A maximum of 16 nodules and a nodule fresh weight of 0.505 g were observed in 40-day-old plants upplied basally with 500 mg urea and 100 mg borax/pot. Nodule number and nodule fresh weight increased with increasing levels of boron, however, increasing nitrogen levels decreased them. Nodulation inhibited by urea may be directly associated with the toxic product of NO-,- metabolism i.e., N02~. The maximum leghaemoglobin (Lb) content in nodules was observed in 40-day-old plants supplied with 50 mg boron 10 kg-1 soil. The levels of Lb decreased significantly with increasing concentration of applied urea, probably due to accumulation of N03~ and NC>2_ in the nodules resulting in the formation of nitrosylleghaemoglobin (LbNo). A significant increase in Lb content of nodules of these plants was observed with increasing levels of boron upto 100 mg borax 10 kg-1 soil.|
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