Nuclear DNA content in turnip [Brassica rapa] root cortical and callus cells infected with Plasmodiophora brassicae: Studies on the clubroot of cruciferous plants (8)

In clubroot on turnip in cruciferous vegetables, cortical tissue and callus tissue cells infected with Plasmodiophora brassicae Woronin were employed for the present study. The relative nuclear DNA content in their cells was compared with healthy cells to obtain some data to clarify the mechanism of cell hypertrophy. Small pieces of young clubs on two susceptible cultivars to clubroot of turnip and infected callus tissues were fixed in acetoethanol fluid and then stored in 70% ethanol in a refrigerator until used. After hydrolysis in a5N HCl at 25 degrees C for 40 minutes, the samples were stained for 4-5 hours by Schiff's reagent at room temperature. The nuclei in tissue samples which were slightly crushed were used for measurements. Fresh leaves of Camellia sasaqua Thunb., in which Feulgen stain was consistently observed, were treated on the same slideglass as the standard. Microspectrophotometric measurements were made 30 nuclei per sample at the maximum absorption wavelength of 560 nm with a scanning microdensitometer, Nikon Vickers M 85. Two kinds of nuclei of 2C and 4C were found in healthy and infected cortical tissues cells, and variational width of unclear DNA content of infected cells was large. Nuclei of 8C and higher DNA classes were also recognized. Both 2C and 4C nuclei were observed in healthy and infected calli and variational width of infected cells with more DNA content than 4C was large. In infected turnip cortical and callus cells, the relationship between the number of nuclei in a plasmodium in an infected cell and the nuclear DNA content in the cell showed a high correlation of r=0.83 in "Waseo-kabu", r=0.64 in "Taibyohikari-kabu" and r=0.73 in infected callus cell. From the above results, the abnormal metabolism in infected cells, the increased nuclei DNA synthesis accompanied with the growth of vegetative plasmodium in a cell and the disturbance of normal somatic cell division, were suggested