Effects of salicylhydroxamate on respiration, seed germination and seedling growth in Avena fatua

Abstract

The effects of inhibitors of alternative respiration [salicylhydroxamate (SHAM) and propyl gallate (PG)] on germination, seedling growth and O2 uptake in Avena fatua L. (wild oats) were studied. SHAM did not inhibit germination or O2 uptake prior to germination. SHAM‐sensitive (alternative) respiration, therefore, cannot be a pre‐requisite for germination. Following germination, both chemicals inhibited seedling growth with the root being more susceptible than the shoot. SHAM concentrations that inhibited root growth by 90 to 95%, inhibited O2 uptake of 1 cm root apices by less than 15%. While sodium azide (a cytochrome‐oxidase inhibitor; 1 mM) alone inhibited O2 uptake by only 40 to 50%, in the simultaneous presence of SHAM (or PG), O2 uptake was inhibited by 90 to 99%. Thus: 1) respiration of wild oat seedling root apices is predominantly cytochrome‐mediated and incomplete inhibition of O2 uptake in the presence of azide alone is due to diversion of electrons to the alternative pathway and 2) even though these roots have little alternative respiration, they maintain the capacity to support a much greater flux of electrons via this path way. SHAM and PG at concentrations (0.05 to 0.4 mM) which inhibited O2 uptake significantly in the presence (but not in the absence) of azide had little effect on root growth suggesting that an effect(s) other than that on respiration is involved in the inhibition of root growth at higher concentrations. The effect of SHAM on wild oat root growth is not selective as it also inhibits growth of a number of crop species.