The effect of NH4 and N03 supply in the nutrient solution on nitrate reductase activity (NRA) was Investigated in leaf and root of Golden delicious apple trees were grafted on M9 rootstock. This research was performed in Factorial experimental in randomized completed design during a period of three years in 1993-1995 at the research glasshouse and laboratory of agricultural college of Tehran University. Two-year-old trees were planted in plastic pots containing sand and perlite with provision for drainage, and graffted.
After two weeks. The trees were supplied with coib nutrient Solution and compared with four levels of NH4+ I NH4 + No- (0.14,2.14, 4.14, 6.14, 8.14).Sampling prosses is consist of four time in year.
Increasing NH4+ I NH4 + No3- ratio significanty decreased NRA in leaves and roots, but significant an increasing in response to 8/14 and decease to 0/14 ratio in leaves as observed.
The occurrence of NRA in apple leaves was significantly greater than those of roots and it can therefore be conculded that the reduction of nitrate can occur in various organs of apple trees but that is greater in leaves.
In addition two reduction time assay resulted on activity of the enzyme per gram fresh weight per hour approximately 24 fold higher for half hours than that obtained with one hour reduction time.
A seasonal patterns study indicated that NRA were high at growth stages and declined on warm months.
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