Characteristics of ³⁶ClO₃⁻ influx into nitrate reductase deficient mutant E₁ Pisum sativum seedlings: Evidence for restricted ‘induction’ by nitrate compared with wild type

The characteristics of nitrate uptake into seedlings of Pisum sativum L. cv. Rondo mutant E1 defective for nitrate reductase (NR) and of its parent variety Rondo have been investigated using 36ClO3− as an analogue for nitrate. The apparent Michaelis Menten constants (Km) for 36ClO3− influx measured over 10 min were similar for mutant E1 and the wild type (Wt). There was a 28% increase in 36ClO3− influx into Wt seedlings following nitrate pretreatment but this was not found when mutant seedlings were used. N starvation increased 36ClO3− influx into both mutant and Wt seedlings, and the rate of cycling E/I was also enhanced to a similar extent. The results are discussed in terms of current ideas on the regulation of nitrate uptake and assimilation.