THE PHYSIOLOGICAL-BASIS OF SEED DORMANCY IN AVENA-FATUA .6. RESPIRATION AND THE STIMULATION OF GERMINATION BY ETHANOL

Ethanol induced germination in several partly after-ripened dormant lines of A. fatua L. The dose-response curves for the stimulation of germination and for O2 uptake were similar, indicating that ethanol may stimulate germination by promoting O uptake. A time-sequence study showed that ethanol stimulated O2 uptake by as much as 70% prior to the 1st visible signs of germination. A similar methanol treatment failed to induce germination or significantly elevate O2 uptake, indicating that the promotive effects of ethanol are not common to all alcohols. The stimulation of both germination and O2 uptake by ethanol was not inhibited significantly by salicylhydroxamic acid, an inhibitor of alternative respiration. Thus, stimulation of germination and O2 uptake by ethanol does not require the operation of the alternative pathway of respiration. Similarly, the stimulation of germination and O2 uptake by ethanol were not inhibited by sodium azide, an inhibitor of cytochrome-mediated respiration. However, both germination and O2 uptake were prevented when salicylhydroxamic acid and sodium azide were administered together. Thus, stimulation of these events by ethanol requires only the operation of one or other of these pathways of respiration; a specific requirement for the operation of the alternative pathway of respiration does not exist. The function of ethanol as a promoter of respiration is discussed with reference to dormancy and involvement of the Krebs cycle.