On the Oxidation-Reduction Potential of Tissue Fluid of the Rice Plant : II. Redox Potential as Influenced by Light Intensity and water Temperature III. Changes in the Redox-Potential of the Leaf by the Growing Stages of the Plant IV. Varietal Differences in Redox-Potential of the Leaf

[摘要] To make clear the physiological significance of redox-potential of tissue fluid of the rice plant some experiments were conducted. The Eh value of tissue fluid was determined electrically using homogenate of tissue obtained by means of Waring Blendor. 1. According to our previous work the Eh value on a fine day begins to descend with the sunrise, arrives at a minimum value after noon, and rises again thereafter. To explain the cause of this diurnal changes in Eh value some experiments concerning the influence of light intensity and water temperature on the Eh value were carried out (Table l, 2). The usual course of diurnal changes in Eh value of leaf was changed by shading on a fair weather. That is, temporary shading delayed often the time of descent of Eh value during the day, causing in general a slight rise in its daily average value, while cantinued sheding decreased the diurnal range of Eh value, causing a considerable rise in its daily avarage value. Lower water temperature than optimum lowered the Eh value of shoot and root (Table 3). From these facts the diurnal changes seen on fair weather seem to be caused by sunlight, presumably through its inflnence upon the photosynthetic activity of the leaf. 2. Eh value of the leaf was determined at 6 a. m. every 3-7 days throughout the whole growth cycle of three varieties (Fig. 1). Regardless of the variety the Eh value of leaf ascended generally with the progress of growth stages, arriving at a maximum value in late August and early September and descended afterward with the approach of harvesting time. The Eh value showed some fluctuations; descending on a continued fine weather and ascending on a continued bad weather. 3. Varietal differences in the Eh value of leaf were studied using adult plant grown in a paddy field (Table 4). Varieties having a high resistance to "Akiochi", root-rot and Sesame leaf spot showed generally a high Eh value of the leaf as cnmpaired with those having a low resirtance.

[学科分类] 农业科学（综合）