The Effect of pH on the Action of Respiratory Inhibitors in Avena fatua Seeds

The effects of pH on the action of sodium azide, a cytochome-oxidaseinhibitor, and salicylhydroxamate (SHAM), an alternative respirationinhibitor, on the respiration of dormant seeds of wild oat (Avenafatua L.; line AN-51) were studied. While pH had little effecton seed respiration in controls, it strongly affected the activityof azide. One mM azide inhibited seed respiration at pH5, butstimulated it at pH 7. SHAM (10 mM) completely inhibited thestimulation of respiration by 1 mM azide in an unbuffered medium,but failed to do so when the medium was buffered at pH 7. Inunbuffered medium, 10 mM SHAM actually augmented the stimulationof respiration by 0.25 mM azide to the same degree as when theazide solution was acidified to mimic the pH change incurredwith dissolution of 10 mM SHAM. These results suggest that theinhibitory effect of SHAM on the action of azide in an unbufferedsystem may in part be due to its acidification of the incubationmedium rather than by the inhibition of alternative oxidase.Lower pH favours the formation of the undissociated hydrazoatemolecules causing greater inhibition of cytochrome-oxidase andother azide-sensitive enzymes. Avena fatua L, wild oat, seed dormancy, azide, salicylhydroxamate     

Action of Respiratory Inhibitors on Seed Germination and Oxygen Uptake in Avena fatua L.

The effects of sodium azide, potassium cyanide (cytochrome oxidaseinhibitors), and salicylhydroxamic acid (SHAM; an alternativerespiration inhibitor) on germination and respiration of Avenafatua L. seeds were studied. Azide and cyanide released seeddormancy at similar concentrations and treatment durations.Cyanide, however, stimulated germination of seeds with littleafter-ripening, whereas azide had no effect under similar conditionsunless the seeds were after-ripened for several months; theduration of after-ripening required for seeds to respond toazide varied with seed batch. There was also a greater lag priorto germination in the case of azide, compared to cyanide treatedseeds. SHAM inhibited the stimulation of germination and respirationby azide, but not by cyanide. Furthermore, respiration induced by azide or cyanide could notbe inhibited by the subsequent application of SHAM. These findingssuggest that the respiration stimulated by azide and cyanideis not alternative (SHAM-sensitive) and, therefore, this respiratorypathway cannot be involved in the stimulation of germinationby cytochrome oxidase inhibitors. While embryos excised fromcontrol, azide or cyanide pretreated seeds had the capacityto perform alternative respiration, the actual contributionof this pathway was negligible. A large proportion of respirationof embryos excised from azide or cyanide pretreated seeds wasresidual, i.e. insensitive to both SHAM and cyanide. Alternative respiration, azide, cyanide, dormancy, salicylhydroxamic acid, wild oats