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Title: IAA METABOLISM IN LEMNA GIBBA UNDERGOES DYNAMIC CHANGES IN RESPONSE TO GROWTH TEMPERATURE

Author
item RAPPARINI, FRANCESCA - BOLOGNA, ITALY
item TAM, YUEN YEE - UNIV OF MASSACHUSETTS
item COHEN, JERRY - UNIV OF MINNESOTA
item Slovin, Janet

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: The responses of plant tissue to stress caused by exposure to high or low temperature conditions are controlled by the interaction of several plant hormones. In many cases, temperature stress negatively impacts plant growth. To understand the role of one plant hormone that is important in controlling the rate of plant growth, we measured several properties of the metabolism of this hormone, auxin. We show for the first time that growth under low and high temperature conditions results in activation of entirely different pathways for the production of auxin. In addition, changes in auxin levels and its rate of turnover also appear to be temperature sensitive. Auxin is involved in a number of important processes in plant tissues, such as cell expansion, root formation, fruit development, and control of fruit abscission. Our new information on how auxin is regulated at different growth temperatures has many potential uses for crop improvement in processes important to production and storage. This information should be of importance to molecular biologists, plant breeders, and others interested in development of improved plant varieties by biochemical, genetic or molecular techniques as well as producers, consumers and others interested in the benefits possible through crop genetic enhancement techniques.

Technical Abstract: The metabolism of indole-3-acetic acid (IAA) was studied in relation to one environmental variable, growth temperature. The model system used was an inbred line of the aquatic monocot Lemna gibba G-3, 3F7-11, grown at temperatures ranging from 5 to 35C. IAA levels, the rate of IAA turnover, and the patterns of label incorporation from IAA precursors were measured using stable isotope-mass spectrometric techniques and evaluated relative to growth at the experimental temperatures. IAA levels exhibited unusually high variability in plants grown at 15 to 20C. Turnover rates were quite rapid throughout the range of experimental temperatures except at 25C, where IAA turnover was notably slower. These results suggested that a transition occurred over these temperatures for some aspect of IAA metabolism. Analysis of [15N]anthranilate and [2H5]tryptophan incorporation into IAA showed that tryptophan dependent biosynthesis predominated at 15C however, there was a shift in pathway such that tryptophan-independent biosynthesis of IAA was the major route to IAA at 30C. The effects of growth temperature on auxin levels have been reported previously, however, no prior studies correlated these effects with the pathway for IAA production.