Seed dormancy in red rice : v. Response to azide, hydroxylamine, and cyanide.

The activity of NaN(3) (0.5 millimolar), hydroxylamine-HCl (10-18 millimolar), and potassium cyanide (1 millimolar) as dormancy-breaking agents of dehulled red rice (Oryza sativa) is pH-dependent such that medium pH values favoring formation of the uncharged chemical species resulted in the highest germination percentages. There was no promotive effect of pH itself in the range of 3 to 10. The minimum contact times for maximum response (>/=90% germination) to NaN(3), KCN, and NH(2)OH-HCl are 8 hours at pH 4, 24 hours at pH 8, and 72 hours at pH 6 or 7, respectively, for exposure commencing at the start of imbibition. Dehulled seeds, imbibed first in water, show only slightly reduced germination when subsequently transferred to solutions of dormancy-breaking chemicals.Intact seeds remain dormant in the presence of NaN(3), KCN, or NH(2)OH-HCl unless partially dry-afterripened. The pH dependence of these chemicals is reduced in intact, afterripening seeds.