ASGSB 2003 Annual Meeting Abstracts


MODIFICATION OF GROWTH AND GRAVITROPIC RESPONSE IN MAIZE ROOTS BY RETINOIC ACID.   Timothy J. Mulkey    Life Science Dept., Indiana State University, Terre Haute, IN  47809

   Retinoids are a family of molecules that are related to β-carotene and vitamin A.  In animal systems, the retinoids are required by a variety of systems including reproduction, vision, and maintenance of epithelial cells.  The effects of retinoic acid in growth and gravitropic response was examined by comparing the effect of cis and trans isomers of retinoic acid on elongation rate, hydrogen ion secretion, Ca+2 asymmetry during gravistimulation, and protein phosphorylation in primary roots of maize.  cis-RA was more effect than trans-RA on promoting root elongation.  After an initial transitory inhibition of root elongation with 10 μM cis-RA, the rate of elongation increase by 200% over 4 hrs.  trans-RA at 10 μM does not significantly alter elongation of primary roots of maize.  Pretreatment of roots with 10-7 M trans-RA and exposure  to 1 ÁM and 0.1 ÁM IAA results in inhibition of growth similar to IAA controls.  Roots pretreated with 10-7 M cis-RA for 2 hours with subsequent exposure to 10 nM to 0.01 nM IAA exhibit an initial inhibition with subsequent recovery in the rate of elongation.  RA altered the pattern of gravitropic response in intact maize roots; the response to RA appears to result from alteration of elongation and modification of calcium redistribution in the apices of gravistimulated roots.  Previous data indicates that gravitropic stimulation alters protein phosphorylation patterns in gravistimulated roots.  In this study, RA alters the in vitro phosphorylation of a 63 Kd protein membrane protein and the in vitro phosphorylation of a 51 Kd protein cytoplasmic protein.  This data suggests that retinoic acid promotes elongation, alters the auxin response, alter Ca+2 asymmetry during gravistimulation, and modifies the protein phosphorylation patterns observed in roots.


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