Effect of plant growth regulators on nitrate uptake and its reduction in radish cotyledons

Pretreatment of radish (Raphanus sativus L.) seedlings with exogenous hormones in the absence of external nitrate, resulted in a system having enough hormone levels to mediate the responses or activate the metabolic pathways which are necessary for nitrate (NO₃) uptake and reduction. Effects of pretreatment of radish seedlings with KN, GA, and ABA on the induction of NO₃ transport and corresponding NR activity, upon exposure to NO₃ were investigated. A low NO₃, uptake rate was observed with hormones when compared to DW‐control, while its induction pattern exhibited a sort of biphasic kinetics. It was observed that each hormone treatment affected NO₃ uptake and reduction specifically at different ambient concentrations of NO₃. On the basis of this, the operation of different constitutive and inducible (CHATS, LATS, HATS, and IHATS) transport systems was resolved for different hormonal treatments. Further, the hypothesis that nitrate uptake has direct role on nitrate reduction was supported by all treatments, except KN where highest NR activity despite lowest NO₃ uptake, was recorded. The results with KN points towards enhanced NR mRNA and de novo synthesis of enzyme.