キュウリモザイクウイルス感染タバコ葉におけるポリフェノールオキシダーゼ活性の推移とウイルス濃度との関係

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The purpose of this study is to find the changes in po1yphenoloxidase (PPO) activity in cucumber mosaic virus (CMV) infected tobacco1eaves at various periods after inocu1ation, and to hind the effect of this enzyme on the changes in symptoms and virus concentration in vivo, which have been described in previous reports. Lower two 1eaves of tobacco seed1ings (Nicotiana tabαacum L. cultivar Bright Ye11ow) were inoculated with ordinary strain of CMV (CMV-O), in an air-conditioned glasshouse at 25℃. PPO activity in the systemica11y infected upper three leaves was measured by the rapid method described by Shiroya, at weekly intarval for 4 weeks after inoculation. Ch1orogenic acid was used as the substrate of PPO reaction. PPO activity in the leaves increased from the 8th day to the 21st day after inoculation, and on the 14th and the 21st day the activities were significantly higher than those in healthy contro1 1eaves. On the 21st day, the difference of activities between infectedand healthy leaves was highest, and reached 2.5 times on the basis of tissue dry weight. On the 28th day the enzyme activity decreased to the same level as on the 8th day (Fig. 2). These changes in enzyme activity were inversely proportional to the changes in symptoms and Virus concentration in vivo. PPO activity in leaf extracts of tobacco plant grown in copper-deficient culture solution is known to decrease to about l/10-1/25 of control non-deficient leaves, even when the sign of deficiency is not apparent. Tobacco plants were grown in Cu-deficient cuture solution prepared principa11y by the method of Staut and Arnon, and inoculated with CMV-0. About two weeks after inoculation, greyish brown spots appeared on the 1ower leaves, as a sign of deficiency. During 4 weeks after inoculation, top leaves were harvested at weekly intervals, and homogenized with phosphate buffer (0.1 M, pH 7.O) containing l/30 M Na-diethyldithiocarbamate. Infectivity in Cu-deflcient and non-deficient leaves was compared by inoculation onto opposite primary leaves of cowpea. Changes in infectivity of Cu-diflcient leaves were simi1ar to those of non-deficient leaves (Fig. 5). Very 1ow infectivity and masking of symptoms in newly deve1oped leaves were obtained on the 21st day, even in Cu-deficient plants. The results were confirmed by using standard inoculum of vacuum-freeze dried infected leaf tissues and by serologica1 assay. When Cu-deficient leaves were homogenized with purifled ye11ow strain of CMV, the infectivity was 2.5-5 times higher than that of contro1 inoculum with non-deficient leaves. In homogenate of Cu-deficient leaves, browning of sap was hardly detectable, whereas then on-deficient leaf sap showed strong browning. These results seem to indicate that deficient leaves has very 1ow PPO activity, in agreement with Shiroya's previous finding. It appears that PPO is not directly responsible for the changes in symptoms and CMV concentration in vivo.
1969-01-25

キュウリモザイクウイルス感染タバコ葉におけるポリフェノールオキシダーゼ活性の推移とウイルス濃度との関係

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