RESPIRATION OF MOSAIC-INFECTED TOBACCO PLANTS

There has been reported in the literature a number of attempts to observe in vitro the respiration of virus preparations in an effort to detect direct evidence of a valid metabolic activity. EATON (10) studied manometrically the respiration of cultures of Staphylococcus lysed by bacteriophage and found a detectable amount of oxygen absorption and carbon dioxide production. On the other hand, BRONFENBRENNER (2, 3) BRONFENBRENNER and REICHERT (4), BACHMANN and WOHFIEL (1), WOHFIEL (19), PARKER and SMYTHE (15), and WYND and BRONFENBRENNER (21), using several types of extraordinarily sensitive procedures, were unable to observe any evidence of a respiratory metabolism by preparations of bacteriophage. PnIRI and HOLMES (16) reported that Agalactia virus absorbed large amounts of oxygen when suspended in a saline solution containing lactate, and these authors believed, therefore, that virus particles were living organisms. The respiratory rates of green plants infected with virus have also received a considerable amount of study. BUNZEL (5) remarked that sugar beets stunted by the Curly-top disease suffered from a "fever." Later (6) he stated that, a respiratory study of these "feverish " plants would be highly desirable in the effort to interpret the more exact nature of the disturbances which the disease produced. THUNG (18) reported that potatoes infected with leaf-roll eliminated more carbon dioxide than healthy tissue, although a study of his data shows that this was not always true. DUNLAP (9) studied the rates of carbon dioxide production of a number of species and found that the virus-affected plants exhibited an increased respiration in their younger tissues and a decreased rate in the older tissues. He observed the mosaic leaves of tobacco, tomato, pokeweed (Phytolacca decandra), cucumber, and raspberry, and yellows-affected leaves of peach, plum, aster, and ragweed (Ambrosia). The conclusions of DUNLAP (9) were criticized by CALDWELL (7) because the data were obtained from tissues respiring in an atmosphere of reduced oxygen content. Further, he doubted if efficient absorption of carbon dioxide was obtained under the condition of the experiment. He also believed that the period of the observation was too short. CALDWELL collected in barium hydroxide the carbon dioxide produced and titrated the remaining alkali after 48 hours. He found an increased carbon dioxide production by virus-infected tomato plants. LEMMON (14) made an extensive study of the comparative rates of metabolism of healthy and mosaic-infected tobacco leaves and found that the diseased leaves always had a lower respiratory rate than normal leaves. His data were expressed in terms of the fresh weight of excised discs of tissue. He further observed that discs of healthy tissue weighed only 85 per cent. as much as did the equal discs of diseased tissue.