Role of phytohormones in nitrate uptake and in vivo nitrate reductase activity of mustard cotyledons

• Published in: Journal of plant nutrition 1999-08, Vol.22 (8), p.1279-1290
• Main Authors: Saroop, Sant, Chanda, Sumitra V., Singh, Yash Dev
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical agents; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Growth and development; Growth regulators; Plant physiology and development; Vegetative apparatus, growth and morphogenesis. Senescence
• ISSN: 0190-4167; 1532-4087
• DOI: 10.1080/01904169909365712

In vivo nitrate reductase activity and nitrate uptake in gibberellic acid (GA)-and kinetin (KN)-treated mustard (Brassica juncea Coss. cv. T-59 Varuna) seedlings grown in the presence of light were investigated. An attempt was also made to determine the metabolic pool size and in vivo apparent K m value of nitrate reductase (NR) for nitrate (NO 3 ). Both NO 3 uptake and in vivo NR activity showed biphasic saturation kinetics, but causal relationship between them was not evident. Kinetin inhibited uptake and promoted in vivo NR activity, while although GA promoted uptake, in vivo NR activity was almost equal to distilled water (DW) control. The hormones affected the K m value differently, GA showed lower K m value while KN showed higher K m value for NO 3 . Metabolic pool size (MPS) was also significantly affected by both the hormone treatments. The results are discussed in relation to the use of in vivo NR activity for calculating the apparent K m and MPS for NO 3 .