Poster: Tropisms

Abs # 671: Red-light regulation of ethylene biosynthesis and gravitropism in etiolated pea stems

Presenter:	Harrison, Marcia A., harrison@marshall.edu
Authors	Harrison, Marcia A. (A)
Affiliations:	(A): Marshall University

During stem gravitropism, the asymmetrical distribution of the auxin causes differential growth and upward curvature while the gaseous hormone ethylene plays a modulating role in regulating the kinetics of growth asymmetries. Light also contributes to the control of gravitropic curvature, potentially through its interaction with ethylene biosynthesis. In this study, a red-light pulse treatment was evaluated for its effect on ethylene biosynthesis during gravitropic curvature in etiolated pea epicotyls. Ethylene biosynthesis evaluation included measurements of ethylene; the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC); malonyl-conjugated ACC (MACC); and in vivo ACC oxidase activity. Relative RT-PCR was used for expression studies of pea ACC oxidase (Ps-ACO1), and ACC synthase (Ps-ACS1, Ps-ACS2) from total-RNA extracts of epicotyl tissue. For red-pulse treatment, dark-grown seedlings were given a 6 min pulse of 11 mmol m^-2 s^-1 red light 15 h prior to horizontal reorientation. Red-pulse treatment reduced ethylene production but did not affect ACC or MACC levels. During gravitropic curvature, ethylene production increased from 60-120 min after horizontal placement in both control and red-pulsed epicotyls. In red-pulsed tissues, ACC levels increased by 120 min while MACC accumulated in the lower portion of horizontally placed tissue at 60 min after horizontal placement. In controls, MACC levels decreased during curvature. ACC oxidase activity was not altered by light treatment or during curvature. Preliminary RT-PCR results support light regulation of Ps-ACS. Further investigations will focus on the expression of ACS and ACO in upper and lower epicotyls flanks during gravitropism.