Respiration of barley roots: Assessment of activity of the alternative path using SHAM.

Bingham, I. J.; Farrar, J. F.

The activity of the alternative path of O2 consumption in detached and intact roots of barley [Hordeum distichum (L.) Lam. cv. Maris Mink] was determined by titration with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. In the absence of cyanide, only high concentrations were inhibititory (> 5 mM), whilst in its presence low SHAM concentrations (2.5-5.0 mM) gave maximum inhibition; the resulting ϱValt plots were non-linear. A SHAM-stimulated peroxidase could readily be washed from these roots, but non-linearity cannot be explained in terms of SHAM-stimulation of this peroxidase as it is not active in the absence of an exogenous supply of NADH. In detached roots the degree of inhibition of respiration with 25 mM SHAM was nearly double the capacity of the alternative path (measured as the degree of inhibition by SHAM in the presence of cyanide), suggesting non-specific inhibition. Effects of SHAM on cytochrome path activity in intact roots were examined by reverse titration with cyanide in the presence and absence of SHAM. At 5 mM SHAM had no effect on the cytochrome path, but at 25 mM it inhibited. We conclude that the only factor causing non-linearity of ϱValt plots in barley roots is non-specific inhibition of the cytochrome path by high concentrations of SHAM; consequently only low concentrations of SHAM (2.5-5.0 mM) are suitable for estimating alternative path activity in barley roots.

BARLEY; HEMOPROTEINS; OXIDOREDUCTASES; HYDROGENASE; CYTOCHROME oxidase; PEROXIDASE

Physiologia Plantarum, 1987, Vol 70, Issue 3, p491

0031-9317

Academic Journal

10.1111/j.1399-3054.1987.tb02848.x