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Title: AUXIN METABOLISM IN LAND PLANTS

Author
item SZTEIN, A - UNIVERSITY OF MARYLAND
item Cohen, Jerry
item Slovin, Janet
item COOKE, TODD - UNIVERSITY OF MARYLAND

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: The development of higher plants is regulated by plant hormones that determine everything from shoots growing upward to the amount of vascular tissue formed. Molecular technology now allows changes in hormones, but we know little how hormone metabolism evolved as plant complexity increased. The paper reports on the capacity of plants, from early land plants to the most modern forms, to metabolize the plant hormone, indole-3-acetic acid (IAA). The results show that increased complexity of vascular tissue evolved along with the ability to form specific conjugated forms of IAA. These studies should be important to evolutionary biologists, as well as molecular biologists, forestry biologists, and agricultural scientists interested in changes in vascular tissue in plants. In addition, this work should be useful to students and educators interested in how development and hormone metabolism are associated. This work should allow a more critical analysis of the consequences of changing hormonal metabolism by molecular modification such that improvements in quality of fruit production and improved wood yield from forestry trees can now be more rationally designed.

Technical Abstract: The plant hormone auxin (indole-3-acetic acid, IAA) appears to control many plant developmental processes, and studies performed in seed plants suggest that IAA conjugation is the critical mechanism to regulate free IAA concentration. The purpose of this investigation is to characterize the biochemical ability of one charophyte and 23 land plants ranging from liverworts to angiosperms to produce IAA conjugates, and to study the complexity of their conjugation patterns. Actively growing tissue was incubated with 14C-IAA, after which labeled IAA conjugates were separated using thin layer chromatography. The conjugates were analyzed using radioimaging techniques and their tentative identity assigned by co-chromatography and/or by differential hydrolysis. The charophyte and the liverworts appear unable to conjugate IAA. The mosses and the hornwort are able to conjugate IAA into a few amide and ester conjugates. The tracheophytes examined synthesize several conjugates unique to the vascula plants, indole-3-acetyl-aspartic acid (-glutamic acid) and/or indole-3-acetyl-B-1-O-glucose, as well as a variety of other amide and conjugates. These three conjugation patterns are correlated to the type of conducting tissue characteristic of the plants analyzed. These biochemical differences may be indicative of significative differences in the hormonal regulation in these plant groups, thus suggesting that changes in IAA regulation accompanied the major evolutionary events in land plants.