Studies on the Metabolism of Plant Neoplasms

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Abstract
Tomato plants (var. Bonny Best) were grown in loam soil in a greenhouse room and when they were 30 cm. tall, the topmost internode was severed below the node. Test plants were inoculated with a single colony isolate of an attenuated strain of crown-gall bacteria by means of a needle puncture 1 cm. below the cut surface, whereas control plants received a sterile puncture. Inoculated plants and controls were divided into 2 lots. The 1st lot was immediately treated on the cut surface with .01 ml. of a 2.5% paste of gamma-indole-n-butyric acid in lanolin, and at various time intervals from 0 to 240 hrs. after inoculation the auxin paste was removed by slicing off a .2 mm disk of tissue from the top of the stump. The 2d lot received auxin paste at time intervals from 0 to 480 hrs. after inoculation. Axillary buds were removed as soon as they became visible to minimize native auxin supply in the tissues. With the 1st lot, removal of auxin prior to 36 to 48 hrs. after inoculation prevented the appearance of tumors, whereas from 36 to 60 hrs. after inoculation and application of auxin, the eventual size of the tumors appeared to be a function of length of auxin presentation time. Evidence that auxin already moved into the tissues may have induced some tumor-promoting action was found in the formation of limited auxin tumors when the auxin was removed 24 hrs. after application. When auxin was removed after varying periods of time exceeding 60 hrs., there were no significant size differences among the tumors formed. Tests on the 2d lot showed that application of auxin up to 10 days after inoculation induced tumor growth, but when 15 or more days elapsed between inoculation and application of auxin, the resulting tumors had root primordia. The various stages in the formation of crown-gall tumors are discussed. The initial or transformation period includes 2 major phases, the pre-inception and inception phase, involving extensive biochemical changes, and the promotion and completion phase involving a series of cytological, biochemical and physiological changes, during which auxin is required as a promoting agent or "cocarcinogen." The 2 or duplication period involves rapid and un-coordinated cell division and is followed by the differentiation and organization period, when the tumor cells become organized into a definite structural, functional, and relational entity.