On the growth inhibition of the bud in dormant potato tubers

Abstract

Some of the characteristics of starch alteration have been studied by microchemical method. In dormant tubers, as were well known, microchemical evidence was in favor of polysaccharid formation rather than of its decomposition, while several parts of a stimulated bud region (Fig.1) examined were not always uniform in the reaction with dilute iodine acetic acid. When exposed to high temperature (35°C-40°C) the characteristic iodine color of the polysaccharides synthesized was clearly recognized as seen in later stage of tuber formation, while the starch decomposition occurs along small vascular route (a in Fig. 1). Sprouted tubers stained the same shade with iodine in this parts. Further suggestive evidence indicating that the relationship between the phosphorylase activity and preventive effect of cell sap may be closely established was seen microscopically by glucose-I-phosphate reaction on starved slices. Juice obtained from dormant tubers seems to prevent the supply of essential elements which is required for the release of rest nucleus. In view of starches stained with a variety of iodine acids, it is reasonable to state that dormant tubers has a disposition to form polysaccharide, establishing gradually an equilibrium with hydrolysis in adjacent tissue. Within the length from 0.2 mm to 0.5 mm, a mere release of dormant buds can be caused at any time more easily than is expected. Synthetic disposition, however, harness the high tempreratures with drought to force it into re-dormancy, as seen summer crops. Inhibitory cell juice seems to me as a resultant colloidal compound. Thus the release phenomena can not be explained on the basis of specific inhibitor action alone. In view of correlative action of tubers, data observed leads to the conclusion that the dormancy might be due to interprevention of metabolic processes in bud and adjacent part, each involving hydrolysis and synthesis. On the other hand, addition of cell sap of dormant tubers (Fig. 1 b and c) results in marked prevention of discolorment of iode-starch complex which has been found to be altered with juice of tubers stimulated by ethylen chlorhydrin or cut wounld (Table 1 and 2). Starch alteration might be expected to be a prerequisite for the postulated hydrolysis with enzyme. Specific inhibitory effect seems to be brought about by combined action of several factors involved in protoplasm. The experiments on protein hydrolysis strongly suggdst that a portion of the effect produced by inhibitory juice of stimulated tubers when exposed to 50°C may be explained on the basis of an enzyme inhibition.