Studies on the Phytopathological Chemistry of Black-rotted Potato

Part 2. Some Factors concerning the Color Changes of the Injured Part

Abstract

The plant tissues usually turn brown, when they are affected by pathogenic microorganisms: Many papers have been published about this problem, but no theory supported by chemical experiments has been established. We have selected the sweet potato infected with Ceratos, tomella fimbriata, so-called “black-rotted” sweet potato, to carry out our experiments.
In this study, the authors examined, from the point of the view mentioned above, the rise and fall of activities of some enzymes and polyphenols which were contained in the injured parts as well as in the sound parts in order to observe the abnormal metabolism caused by the infection. The results summerised are as follows.
The determination methods of the activities of oxidase, peroxidase, and catalase, and the quantity of polyphenols were improved so as to be suitable for our experiments.
It was ascertained that, using the uninoculated sound potato as the control, the oxidase and peroxidase were highly activated and polyphenols were noticeably accumulated in the sound part adjacent to the injured. This abnormal metabolic phenomena were observed more distinctly. in case of sufficient supply of oxygen than in case of lack of oxygen, and more in case of Vari-ety Norin No. 1 than in case of Variety Okinawa No. 100.
As to the reason why the injured part turned brown, it was ascertained that ate first the function of the protoplasm was destroyed and then the oxidation of polyphenols by activated`.oxidase and peroxidase, occurred 'irreversively, and the quinoid substances thus formed were polymerized immediately, as, soon as the cells which were working out the abnormal metabo-lisrn mentioned above were penetrated by this fungus.
The oxxidase and peroxidase of this fungus had some effects on the browning of the tissue though the enzyme activities of-this fungus were weak.
It was observed that the polyphenolic and quinoid substances might inhibit the penetration of the fungus into the cells cooperating with the bitter substances and resins contained in the injured part. The details including the inhibitory activity, of these substances will be published in Part V of this series.
Higher activities of catalase in the injured part was found to be due to the presence of cata-:las, e in the--mycellium of this fungus grown in the injured part.