Responses of Bean and Tomato to Phytomonas tumefaciens, P. tumefaciens Extracts β-Indoleacetic Acid, and Wounding

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Abstract
1. Differential behaviors of axes of bean, tomato, and Bryophyllum inoculated with Phytomonas tumefaciens are due probably to differences in growth patterns of the axes of these plants. 2. Much of the overgrowth may be due to responses to wounds essential to the course and completion of the infection process. 3. The bean is highly disposed following wounding to formation of surface and internal callus and their derivatives, adventitious roots, and root regeneration. The roots are disposed to fasciation. The bean is not disposed to adventitious shoot formation or to nonnodal shoot regeneration. Moderately old hypocotyls developed in air and then encased in wet sand will develop adventitious roots through the full length of the organ. 4. Occurrence of these events at the wound and above it indicates that growth substances play a role in their enactment. 5. Growth substances apparently are formed or activated in all aerial vegetative members of the bean and transported to the central axis where they move mainly downward, but upward and transversely as well. 6. Elongation of hypocotyl, internodes, and development of axillary buds are retarded or inhibited by hormones from divergences of segments of the axis above them. 7. Disposition of an organ to enact these events is conditioned by its hereditary constitution, age, presence or absence of other organs, metabolic status, and environal factors (temperature, moisture, and light). 8. Enactment of these events is influenced by experimentally introduced growth substances (heteroauxones). These seem to be able to augment or to substitute in part for the native growth hormones (autoauxones) of the bean. 9. Different concentrations and amounts of heteroauxin applied to different organs of the bean and tomato under different conditions are able to elicit almost the entire gamut of injuries and injury reactions known to the phytopathologist. This includes tumors. 10. Phytomonas tumefaciens produces β-indoleacetic acid (heteroauxin) when grown in dextrose-tryptophane or in dextrose-tryptophane peptone liquid or solid (agar) medium. The crude ether extract of the non-inoculated media does not contain heteroauxin. The chemical Salkowski and the biological Avena coleoptile tests were used. 11. The crude ether extract elicits symptoms from bean and tomato similar to those induced by inoculation with P. tumefaciens or by treatment with heteroauxin. 12. Heteroauxin is a chemical agent by means of which, possibly in conjunction with others, P. tumefaciens incites galls. 13. Unequal amounts of 3 per cent heteroauxin paste and of crude extract of P. tumefaciens applied to the hypocotyl of the bean elicit practically identical histic and cytic effects. These are cell enlargement, cell division (possibly a consequence of enlargement), and as a consequence of these suppression of normal differentiation and maturation but genesis of new meristems with new differentiations in abnormal sites. Schizogenous cavities are formed, followed by filling with peripheral callus. Differential response by the same tissue or cell to different amounts and concentrations and different responses of different tissues or cells to the same concentration or amount are indicated. Most of the abnormal tissues and cells are pathic in the sense that they have less adaptive capacity for unfavorable environal conditions than have the normal healthy ones. 14. This study indicates that biology must use the concept "causal complex" in attempting analysis of problems in normal and abnormal, healthy and pathic morpho-, organo-, histo-, and cytogenesis. Each constituent of the causal complex is a necessary but not a sufficient cause for the event under consideration. 15. A tentative nomenclature and classification of growth substances are proposed. 16. Hypotheses are advanced suggesting partial explanation of legume nodules, insect galls, forms of roots of bog, muck and mycorrhizal plants, as well as beneficial effects of humus soils, in terms of auxones. 17. Relation of infectivity and other expressions of pathogenicity are discussed.

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