Date of Award


Degree Type


University or Center

Atlanta University (AU)

Degree Name




First Advisor

Dr. Enola L. Stevenson


This investigation of tumor induction by indole-3-acetic acid (IAA) in bean (Phaseolus vulgaris L. var. Romano) embryos represents a further contribution to the body of knowledge on the role that IAA may play in tumorigenesis and other raorphogenetically anomalous growth patterns.

Bean embryos were excised and grown in the dark at room temperature for 8 days in Hildebrandt1s medium supplemented with or without IAA (2mg/l). Gross morphological and light microscopic observations revealed that IAA-induced tumors suppress primary root growth, inhibit shoot growth, disorganize growth due to lateral expansion, promote cell enlargement, and induce adventitious roots.

Scanning electron microscopic observations revealed thib-walled, elongated tiers of parenchymatous cells and some structural as well as functional changes in trichomes.

Biochemical studies revealed that IAA-induced tumors show more DNA and RHA synthesis, whereas protein synthesis remains pretty close to control tissue. The KNA synthesis shows a significant increase (21%) over control. Higher water and K+ ion uptake is evident in tumor tissue. No significant difference in cyclic AMP levels between tumor and control was found.

These observations lead to the conclusion that IAA acts on nucleic acid metabolism which stimulates the loosening of cell walls by synthesizing various enzymes, particularly cellulase. Subsequently cell wall expansion results from increased turgor pressure and an increase in water intake, causing disorganized swelling of target tissue. Furthermore, increased water permeability continues to induce further dis organization, and possibly destruction of vascular tissue, senescenee and death. IAA does not stimulate cAMP synthesis in bean embryos. Depletion of IAA uncouples the inhibitory effect on shoot growth and, subsequently, semi-normal shoot growth results. As such, this tumor in bean embryo is an IAA-dependent one.

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