Abstract
In order to research the influence of cephalothecin upon the secretion of some carbohydrases by the blast fungus, Piricularia oryzae CAV. cultural experiments were carried out using Tochinai and Nakano's synthetic nutrient solution, with addition of Biotin (15-20mr/1cc.) and vitamin B1 (15-20γ/1cc.).
In the solutions. cephalothecin was added at strengths of 1: 5-164. half of the lots was provided with one of the carbohydrates, including sucrose. maltose, soluble starch and cellulose and another half lacked. After 10-days culture at 25°C, determinations of reducing sugars were made upon the cultured solutions.
When the fungus was cultured in cephalothecin solutions with carbohydates, there were increase in dry weight of mycelial mat, and decrease in weight of non-reducing sugars, as against the solutions without any carbohydrate. The differences are shown as M and S respectively. The ratio S: M is temporarily called as the relative secretion value.
When sucrose is supplied as the carbon source, the ratio S: M is highest at the concentration of 1:20 cephalothecin (of. table 5). Such secretions as of sucrase by the fungus may be called sucrase-type. Maltase also belongs to this type.
In the solution containing soluble starch, the value is maximum at the concentration of 1:40 cephalothecin. These phases, which are quite different from those in sucrase-type, may be named amylase-type.
No cellulose was utilized by the fungus in the presence of cephalothecin. This, together with other carbohydrates-emulsin, inulinase, lactase, mannase, pectinase and xylanase-may be included in cellulase-type.
The relative secretion value (S:M) shows the amount of the carbohydrate consumed by the fungus to increase 1mg. of the mycelium in dry weight. Accordingly, for the consumption of 1 mg. of sucrose or soluble starch, the increase in dry weight of mycelium is to be far less in 1:20 or 1:40 solution of cephalothecin than either in 1:80-160 or in the check solution, In 1:5-10 solutions, the growth of the fungus is extremely poor. Thus, the phases of S:M suggests certain connection between the fungus's secretion of carbahydrases under the influence of cephalothecin and the resistance to blast disease of the rice plant treated with cephalothecin.
