PHOTOSYNTHESIS AND RESPIRATION RATES OF LEAVES OF NICOTIANA GLUTINOSA INFECTED WITH TOBACCO MOSAIC VIRUS AND OF N. TABACUM INFECTED WITH POTATO VIRUS X

The rates of respiration and of photosynthesis of tobacco leaves infected with potato virus X were not affected until the leaves showed symptoms; the respiration rate was then increased by more than 30% and the photosynthesis rate decreased by 20%. When local lesions appeared on the leaves of Nicotiana glutinosa infected with tobacco mosaic virus, but not before, the respiration rate was increased by an amount, up to 30%, that varied with the number of lesions. The photosynthesis rate was decreased by 20%, but there was no effect on photosynthesis or respiration until symptoms appeared. These results differ from those previously reported for tobacco leaves infected with tobacco mosaic virus, in which both respiration and photosynthesis were affected within 1 hr. of inoculation. The validity of extrapolating arguments based on the results obtained with other combinations to this commonly used combination and vice-versa is questioned.