NICOTINAMIDE ADENINE DINUCLEOTIDE AND NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE CONCENTRATIONS IN LEAVES OF NICOTIANA GLUTINOSA INFECTED BY TOBACCO MOSAIC VIRUS.

Abstract

WHEN leaves of Nicotiana glutinosa are inoculated with tobacco mosaic virus (TMV) the formation of local necrotic lesions is accompanied by an increase in the rate of respiration1,2. This increase is related to the development of the lesions and to the total number of lesions produced. Although tissue extracts of the lesions show increased polyphenoloxidase activity3,4 evidence is lacking to show that polyphenoloxidase is concerned in the respiration of the intact virus-infected cell or that the increased repiration is related to increased polyphenoloxidase activity. Two possible functions for polyphenoloxidase in the metabolism of the virus-infected cell can be suggested. It may function as a terminal oxidase, and the increased respiration is the result of the increased polyphenoloxidase activity. However, this is most unlikely as the respiration rate in plant tissues is not usually limited by the activity of the terminal oxidases. A second possibility is that increased polyphenoloxidase activity is concerned with the oxidation of polyphenolic compounds to oxidized polyphenols. If this made any significant contribution to the respiration of the virus-infected tissue an increase in the respiratory quotient would be expected, but this was shown not to be so by Yamaguchi and Hirai2 who found in N. glutinosa leaves infected by TMV the respiratory quotient was unchanged.