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Title: THE EFFECT OF EXOGENOUS AUXINS ON ENDOGENOUS INDOLE-3-ACETIC ACID METABOLISM: IMPLICATIONS FOR SOMATIC EMBRYOGENESIS IN CARROT

Author
item RIBNICKY, DAVID - UNIVERSITY OF MARYLAND
item ILIC, NEBOJSA - UNIVERSITY OF MARYLAND
item Cohen, Jerry
item COOKE, TODD - UNIVERSITY OF MARYLAND

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plants contain a variety of chemical compounds called plant hormones which are important for plant growth and development. The auxins are one family of plant hormones used in many different kinds of applications. The application of a naturally occurring auxin results in the inactivation of the auxin within the plant. The application of one synthetic auxin has a similar effect while the application of another synthetic auxin leads to profound differences in metabolism and growth pattern. These results will be important for plant biochemists and molecular biologists interested in how plant hormones work, agrochemical companies working with plant growth regulation and herbicides, developmental biologists interested in the control of plant growth and development as well as any plant biologist, breeder or consumer interested in the regeneration of plants without the need for seed.

Technical Abstract: The effect of auxin application on auxin metabolism was investigated in excised hypocotyl cultures of Daucus carota. Concentrations of both free and conjugated IAA (indole-3-acetic acid), [2H4]-IAA,2,4-D (2,4-dichlorophenoxyacetic acid) and NAA (naphthaleneacetic acid) were measured by mass spectrometry using stable isotope labeled internal standards. 13C1-NAA was synthesized for this purpose, thus extending the range of auxins that can be assayed by stable isotope techniques. 2,4-D promoted callus proliferation of the excised hypocotyls, accumulated as the free form in large quantities and had minor effects on endogenous IAA concentrations. NAA promoted callus proliferation and the resulting callus became organogenic, producing both roots and shoots. NAA was found mostly in conjugated form and had minor effects on endogenous IAA concentrations. [2H4]-IAA had no visible effect on the growth pattern of cultured hypocotyls, possibly because it was rapidly metabolized to form inactive conjugates or possibly because it mediated a decrease in endogenous IAA concentrations by an apparent feedback mechanism. The presence of exogenous auxins did not affect tryptophan labeling of either the endogenous tryptophan or IAA pools which suggests that exogenous auxins do not alter the IAA biosynthetic pathway but the synthetic auxins did appear to be necessary to induce callus proliferation which was essential for excised hypocotyls to gain the competence to form somatic embryos.