Effects of metabolic poisons on rice: the comparative sensitivity of aerobic and anaerobic modes of germination.

Rice germinates equally well when incubated in air and in nitrogen. It was therefore chosen for a comparative study of the effect of oxygen status in a single organism upon the activity of conventional metabolic poisons. Inhibitor activity was based upon the concentration required for 50% inhibition of germination. The inhibitors were: AgNO(3), HgCl(2), phenylmercuric acetate, iodoacetamide, KCN, NaN(3), NaF, fluoroacetate, 2,4-dinitrophenol, Na(2)HAsO(4) and CO. Only 5 inhibitors out of 11 differed significantly in their effects on aerobic and anaerobic germination. These included phenylmercuric acetate (N(2)), sodium fluoroacetate (air), NaN(3) (air), and 2,4-dinitrophenol (N(2)). CO activity was manifest only in air and it was photo-reversible. The effects of CO, NaN(3), and fluoroacetate were consistent with their conventional role in aerobic metabolism. The failure of KCN to discriminate was attributed to its relative non-specificity. 2,4-Dinitrophenol behaved anomalously, requiring a 20-fold lower concentration for inhibition under nitrogen than under air. Among sulfhydryl poisons, only phenylmercuric acetate differentiated between germination in air and nitrogen and was nearly 8 times more active under nitrogen. Uptake measurements using phenylmercuric acetate and arsenate showed both compounds to be in greater concentration under aerobic conditions, thereby rendering unlikely any explanation based upon greater permeability under nitrogen. In addition to other anomalies, the fact that NaN(3), fluoroacetate and CO inhibited anaerobic germination at any concentration requires explanation. It was concluded that the general significance and utility of metabolic inhibitor studies in vivo required further evaluation.