Abstract
The high incidence of sesame-like black spots in the midrib and vein regions of Chinese cabbage leaves has been recognized in Toyama and other prefectures. The symptom of this physiological disorder is so-called Goma-sho. In severe cases, the market price of the Chinese cabbage is reduced markedly.
Data concerning the causes of Goma-sho and its prevention, however, are lacking. The purpose of this study was to investigate the physiological mechanism of Goma-sho. In the present study, the characteristics of this physiological disorder during the growing period of Chinese cabbage under a field condition were surveyed and then the incident regions in midrib and vein tissues were observed by using histological and histochemical methods.
1. Symptoms of Goma-sho in cv. Hibari and Taibyo 60 nichi could be divided into two types. Type 1 occurred in midrib of immature leaves and was closely related to excessive growth of leaf tissue during the early period of growth. Type 2 was found in mature leaves and was connected with a decrease in the ratios of outer to inner leaves.
2. By the histological test, before the appearance of black spots, swelling of granules occurred in disordered epidermal cells, followed by the cell wall becoming brownish. The browning part of the cell wall elongated with the swelling granules and nuclei, and plasmolyzed cells occurred around the browning cells.
3. By the histochemical test, chlorogenic acid and polyphenol oxidase were found in the browning cells, and polyphenol and peroxidase were distributed in the disordered tissue.
4. In the disordered cells, nitrite accumulated around the granules. The granules were also expanded.
