Effect of butyric acid on the germination of the seeds ofPhacelia tanacetifolia

The effect of a weak acid (butyric acid) on the germination of seeds ofPhacelia tanacetifoliaBenth. (cv. Bleu Clair) has been studied. Butyric acid inhibited the early phase of germination, and the inhibition was correlated to the amount of the per‐meant undissociated form present in the incubation medium. The inhibition by butyric acid in the dark was also correlated to a decrease of dark fixation of CO2and to a more pronounced decrease in malic acid levels during the early phase of germination; suggesting that the uptake of the uncharged form of this weak acid was followed by a release of H+ into the cytoplasm, leading to a decrease in its pH. The inhibitory effect of butyric acid in the dark on many metabolic events (rise in respiratory activity, levels of reducing sugars, glucose‐6–phosphate and malic acid, dark CO2fixation, transport activities and macromolecular synthesis) appeared similar to the one of light. Fusicoccin (FC), which directly stimulates the H+pump at the plasmalemma level, ameliorated the effect of butyric acid, as well as that of light, on germination. The bulk of these data is interpreted as suggesting that the mechanism of light inhibition of germination ofPhacelia tanacetifoliaseeds might be the consequence of a general block of metabolic reactivation due to the presence of an unfavourable (acidic) cytoplasmic pH; which might be explained with the lack of the phytochrome‐dependent activation of the H+pump at the plasmalemma level.