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Evaluation of Red-light regulation of ethylene biosynthetic genes by relative RT-PCR.  M.A. Harrison and A.J. Porter. Dept. of Biological Sciences, Marshall University, Huntington, WV.

     Gravitropism is controlled by the interaction of growth-regulating substances and light. While auxin is the primary plant hormone involved in regulating differential growth during stem gravitropism, ethylene modulates the dynamic cellular growth changes associated with upward curvature. Red-light treatment of etiolated seedlings alters the kinetics and curvature pattern along the stem. This red-light effect may result from its inhibition of ethylene biosynthesis, and is supported by studies showing a similar response in stems treated with inhibitors of ethylene biosynthesis or response. The major goal of this project is to evaluate gene expression changes for members of the ethylene biosynthetic gene families ACO (1-aminocyclopropane-1-carboxylic acid [ACC] oxidase) and ACS (ACC synthase) after red-light treatment of dark-grown Arabidopsis seedlings. Relative RT-PCR was used to study the expression of ASC2, 4, 5, 6 and EAT1 (which encodes an ACO), in total-RNA extracts of etiolated Arabidopsis seedlings.  Seedlings were handled under a dim green light and red-treated seedlings were given a 6 min pulse with 11 mmol m^-2 s^-1 red light 18 hours prior to RNA extraction to be consistent with previous studies on the timeline of red-light inhibition of ethylene biosynthesis. 18S rRNA was used as an internal standard. RT-PCR products confirmed low levels of expression for all genes.  Preliminary evidence suggests inhibition of ACS4 after red-light treatment. Continued studies will identify and evaluate the changes in key ethylene biosynthetic enzyme association with gravitropism and after light-pulse treatment.