Respiratory Behavior of Bacteria-Free Crown-Gall Tissues

The respiratory processes of malignant tissues of animals and human beings have long been considered to differ in important respects from those of nonmalignant tissues of the same creatures. This difference expresses itself in several ways, especially in a low R.Q. (0.8 or less) and a decided anaerobic tendency to accumulate acid products, lactic acid in particular. It seems possible, indeed, if we may draw an analogy from plant materials (6, 9), that the characteristic independence from normal morphogenetic restraint shown by tumor tissues may be essentially an expression of independence from the formative influences of oxygen gradients. These evidences of a high degree of anaerobiosis are considered typical of malignant growths, and their possible use in the diagnosis of malignancy has been suggested by some (2, Footnote, p. 242). Routine observations on in vitro cultures of tissues from cancer-like, bacteria-free, crown-gall tissues of sunflower (12) disclosed 3 traits that suggest the existence of a similar picture in plant tumors. In the first place, old cultures have a distinctly yeasty or alcoholic odor. Since this odor, in yeasts, is an accompaniment of an anaerobic type of respiration, it may be interpreted in plant tumor materials as suggesting the accumulation of incompletely respired materials-even when oxygen for complete respiration is available to the tissues. Since these cultures are bacteriologically sterile this accumulation must result from respiratory processes in the tumor tissues themselves. In the second place, such cultures tend to acidify the subjacent nutrient (unpublished data), indicating again the accumulation of incompletely respired, in this case acid, products. There seems to be no general agreement as regards the behavior o f normal plant tissues in this respect. Robbins and Maneval (5) found that excised corn root tips tended to raise the pH of the nutrient, while White (7) reported a lowering of pH by wheat root tips. In the third place, such cultures, when immersed in a liquid nutrient, do not undergo the formative changes evinced by similarly treated cultures of Nicotiana-hybrid tissues, which changes have been attributed to effects of an altered oxygen gradient 1 (9). These observations, together with the obvious possibility of an analogy between these plant tumor cells and those. of animal tumors, led to a more careful examination of the respiratory processes involved. The work reported here is the result of preliminary studies on this problem.