Abstract
Studies have been made on a kind of "Akagare" (I) which is characterized, as the frrst sign, by the appearance of reddish brown spots at the leaf tips. This work has dealt with another type of "Akagare" (II) which occurs on ill-drained paddy soil with excessive humus and is characterized by the occurrence of leaf chlorosis, prior to the appearance of reddish brown discoloration of the leaf. The result of experiments is as follows: 1) Similar trends were observed in the types I and II concerning the causative environmental conditions, seasonal changes in the occurrence of the disease, and abnormalities in the metabolism of affected plants, except that the type II showed a lower response to potash than the type I. 2) Those varieties having a high content of sugar+starch showed a higher root activity such as oxidizing ability of α-Naphthylamine and reducing ability of TTC. They had, as a result, showed a higher resistance to both those types as compared with those having a low content. 3) Both chlorosis and reddish brown discoloration of leaf were sometimes observed when certain harmful organic acids such as butyric, acetic, formic or lactic acids were added to soil or to culture solution. 4) From the above facts and the previously reported works, it is assumed that the occurrence of the type I should be caused mainly by potash deficiency itself in plant, while the occurrence of the type II be mainly caused by intrusion of some harnrful substances (organic acids, excessive Fe, H2S, etc.) into plant. Both types, however, take place through the same disturbance of normal metabolism in plant as shown in Fig 4. Namely, peroxidase activity is enhanced with the turn of respiratory process from the cytochrome oxidase system to another system where H202 is produced. At the same time, Warburg-Dickens-system is activated with the inhibition in glycolysis, acompanying an active production of polyphenols. As a result, polyphenols are oxidized to quinones by peroxidase and combound with amino acids. This leads to the production of melanin-like substances, causing the reddish brown discoloration of the leaf.
