Among the antiviral substances reported so far, antibiotics occupy an important position. Recently it has been shown that blasticidin S, an antifungal antibiotic, inhibits multiplication of tobacco mosaic virus (HIRAI and SHIMO-MURA 1965, HIRAI et al. 1966, brome grass mosaic virus (KUMMERT and SEMAL 1971) and cucumber mosaic virus (JAGANATHAN and RAMAKRISHNAN 1972). Virus infection alters the host metabolism and induces major changes in the physiological processes of the host plant. Since blasticidin S inhibits virus multiplication whidi is closely linked with host plant respiration this investigation was taken up to study the effect of this antibiotic on the respiratory metabolism of the host plant.
Materials and MethodsSattur Samba diilli plants {Capsicum annuum L.) grown under insect-protected conditions were used as test plants. The antibiotic, blasticidin S (BcS) (0.5 ppm), was sprayed thrice at an interval of 24 hours in the control and virus-inoculated plants. The bioAemical changes were studied at an interval of 5 days during a 15-day period in chilli plants subjected to cucumber mosaic virus infection, BcS treatment and a combination of the two.The rate of respiration of chilli leaves was measured gasometrically on alternate days up to 16th day of inoculation by using Warburg's respirometer (UMBREIT et al. 1964). For studies with respiratory inhibitors leaf discs were taken from healthy and inoculated plants and the respiration was studied for 30 minutes by the usual manner and then the respiratory inhibitor in the side arm was tilted into the main diamber of the flask and the experiment was continued for 2 hours. The percentage of inhibition was calculated from the difference in oxygen uptake before and after the addition of the inhibitor. The activity of succinic dehydrogenase was assayed by the manometric method (SLATER 1949).The activities of catalase (DEKOCK et al. 1960), peroxidase (MUDD et al. 1959, ascorbic acid oxidase (HAMPTON 1963), polyphenol oxidase (KRUPKA 1959) and cytodirome oxidase (MERRETT 1962b) were estimated at 5, 10 and 15 days after inoculation.
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