On the Changes of the Terminal Oxidase Systems with Special Reference to the Dormancy of Potato Tubers

Abstract

The present investigation was carried out in order to obtain further information as to whether some respiratory enzyme system in potato tubers of which activity is inhibited by the application of diethyldithiocarbamate (Dieca) and salcylaldoxime, may play any essential participation in the dormancy of potato tubers or not and also whether any difference of respiratory system may exist between the respiration of the dormant tuber and that of the sprouting tuber or not. The results obtained may be summarized as follows. The inhibitions of O2-uptake by the tubers due to the treatments with Dieca or salcylaldoxime were reduced if the tubers were stored previously at low temperature or the dormant tubers were treated previously with gibberellin or thiourea in order to hasten their sprouting. A similar situation was found to be true in the case of the secondary-growth tuber. Judging from the results stated above, it seems quite reasonable to assume that polyphenol oxidase may take part in the respiratory enzyme systems in the dormant tubers and this polyphenol oxidase may play an important role in the dormancy of the potato tubers. The inhibiting effects of Dieca and salcylaldoxime on the O2-uptake of the potato tubers were reduced if when use was made of tubers at their sprouting time and of tubers infected with witches, broom virus which usually show no dormancy. Although the respiration rates of these tubers decreased also under the condition of low oxygen partial pressure of 5 %, a slight respiratory inhibition by the treatment with Antimycin A was recognized. Accordingly, it seems highly probable that some respiratory enzyme system other than polyphenol oxidase may exist in these tubers, but no adequate explanation can be given on the nature of this enzyme system at present. In conclusion, the copper-containing enzyme system, highly presumably polyphenol oxidase and another respiratory enzyme system which is sensitive to low oxygen partial pressure and is not yet identified as to its nature, may play physiologically important roles in dormancy of the potato tubers.