タバコ・モザイク・ウイルス感染葉およびその磨砕汁液におけるuracil-2-<sup>14</sup>Cのとりこみ

Abstract

The incorporation of uracil-2-14C into nucleic acid, phospholipid and protein fractions of tobacco mosaic virus (TMV)-infected tobacco leaves was investigated. Both inoculated and uninoculated leaf disks were floated on water under continuous illumination of artificial light and they were exposed to 14C for 1-5 hours at various intervals after inoculation. Then the disks were homogenized with phosphate buffer and fractionated as described in Fig. 1. The specific activity in each fraction was estimated.The data of Table 1 show that the rate of incorporation of 14C into nucleic acid fraction, or, to a lesser extent, into phospholipid and protein fractions, of inoculated leaf disks 1 and 3 days after inoculation was significanty greater than that into the corresponding fraction obtained from uninoculated leaf disks. However, at 5 days after inoculation, no significant differences in the rate of incorporation into nucleic acid and phospholipid fractions were found between inoculated and uninoculated leaf disks.In order to determine the distribution of the incorporated 14C among the individual bases, nucleic acid fraction was hydrolyzed with 70% HCIO4 and then chromatographed by the method of Wyatt. Table 3 summarizes the analysis of the 14C distribution. A large part of 14C was found in uracil and cytosine, and the specific activity of these bases of inoculated leaf disks 40 hours after inoculation was greater than that of corresponding bases obtained from uninoculated leaf disks.Using cell-free systems, the incorporation of 14C into nucleic acid, phospholipid and protein fractions was studied. Tobacco leaf disks were homogenized with phosphate buffer 22 hours after inoculation and 14C was added to them and the mixture was shaked at 28°C. The data appeared in Tables 5-6. After 2 hours incubation, the rate of incorporation into nucleic acid and phospholipid fractions of inoculated leaf homogenate significantly increased as compared with that of uninoculated leaf homogenate. In this case, the increased amount of radioactivity appeared in nucleic acid fraction was located in both RNA and DNA.Finally, in order to elucidate the general pattern of incorporation of 14C into the various cell fractions, the homogenized juice of leaf disks was fractionated as shown in Fig. 2 and the incorporation into nucleic acid of each fraction was determined. The results are summarized in Table 7. The greater part of radioactivity incorporated into the infected and uninfected cell fractions appeared in DNA of Pl fraction, and specific activity of DNA and RNA in Pl fraction of infected cells exceed the comparable value in uninfected cells 2 days after inoculation.