Levels of desoxyribonucleic acid phosphorus (DNAP) and ribonucleic acid phosphorus (RNAP) were determined at various times during the genesis of tumors and auxin-induced proliferation on stem tissues of broad bean. Prospective tumorous tissues showed a sharp peak of DNAP levels 2 days after inoculation, a maximum depression at 5 days, and a gradual increase to a plateau by 9 days. No marked changes in RNAP were noted. Auxin-induced neoplasms showed a sharp initial rise in RNAP at 2 days after application of IAA, but only slightly elevated DNAP levels.

Initiation of tumor genesis was histologically detected within 2 days after inoculation by increased cambial activity and at 3 days by enlargement of stelar parenchyma. Tumorous tissues showed extensive cell division within 5 days. Complete disorientation of normal stem architecture occurred within 20 days.

Photometric determinations of over 800 Feulgen-stained nuclei of inoculated and control tissues showed no significant increase in relative amounts of DNA per nucleus in tumor tissues during the first 5 days. No evidence for cytoplasmic localization of DNA was found. Although the number of and division of polyploid nuclei may be characteristic of tumorous growth, both wounded and inoculated tissues showed a pattern of DNA values essentially similar to that found in areas of meristematic growth, as compared to mature, nondividing tissues.

Comparisons of histological and cytological findings with biochemically observed changes in nucleic acid levels accompanying crown gall tumor genesis have indicated that the 1- to 2-day peak of DNAP may be a result of specific action of prospective tumor cells, or a product of virulent tumor-inducing bacteria.

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Supported in part by grants from the Dr. Wallace C. and Clara A. Abbott Memorial Fund of the University of Chicago and the United States Public Health Service. This is the seventh of the series of papers on the metabolism of plant neoplasms. We wish to thank Dr. Deana T. Klein for her aid in inoculating and treating the plants and Mrs. Ruth Kleinfeld and Dr. M. Nagaraj for preparing some of the slides.

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