UV-B radiation mediated alterations in the nitrate assimilation pathway of crop plants 2. kinetic characteristics of nitrite reductase

摘要

Cowpea Vigna unguiculata (L.) Walp. cv. Co 4 seedlings were subjected to a weighted irradiance of 3.2 W m~(-2) s~(-1) of biologically effective ultraviolet-B radiation (UV-B, 280-320 nm) and the changes in the kinetic and other characteristics of nitrite reductase (NiR) were recorded. The activity of NiR was hampered by 19 under UV-B irradiation compared to the control. The UV-B treated plants required higher concentrations of nitrate for the induction of NiR synthesis than the controls. The NiR activity decay kinetics showed that the UV-B treatment significantly lowers the t_(1/2) of the enzyme, thereby indicating a reduced rate of enzyme remover. The comparison of kinetic characteristics of nitrate reductase (NR) and NiR under UV-B treatment showed that NiR was not so sensitive to UV-B radiation as NR. As shown by enzyme turnover rates, NiR extracted from plants irradiated by UV-B in situ was less sensitive to UV-B radiation than the enzyme extract subjected to in vitro UV-B irradiation. Though NiR was less damaged by UV-B treatment than NR, subtle changes occurred in its kinetic characteristics.