Abstract
The writers have previously reported a decrease of β-amylase activity in rice leaf tissues surrounding the spots which occured after the inoculation with conidia of Cochliobolus miyabeanus. To clarify the cause of this phenomenon, we have investigated the formation of artificial spots by placing a drop of each solution of such chemicals as respiratory inhibitors, metal salts and phenols, on leaves of rice plants placed in the dark, and the influence of such chemicals on the decomposition of starch present in artificial spots and their surrounding tissues. In view of our exprimental results, these chemicals were divided into three groups as follows: (1) chemicals which form artificial spots and inhibit the starch translocation in rice leaves (Group I), (2) those which form artificial spots, but not inhibit the starch translocation (Group II) and (3) those which have ability neither to form artificial spots nor to inhibit the starch translocation (Group III). We have also investigated the direct or indirect inhibition, by the above-mentioned chemicals, of the activity of β-amylase prepared from rice leaves. All the chemicals belonging to Group I strongly inhibited the activity of this enzyme, whereas most of the chemicals belonging to Group II did not inhidit it. From the results of these experiments, it seems that a substance or substances which inhibit the activity of β-amylase may be produced by the tissues surrounding the spots on rice leaves or by the causal fungus itself.
