Physiological and biochemical characterization of ethylene-generated gravicompetence in primary shoots of coleoptile-less gravi-incompetent rye seedlings.

A recent study demonstrated that gravi-incompetent coleoptile-less seedlings of rye exhibit gravi-competence after exogenous application of ethylene. Treatments and conditions which induce and interfere with this phenomenon were analysed in more detail. Aminocyclopropane-1-carboxylic acid (ACC) as a precursor of ethylene has similar gravicompetence-inducing effects and also appropriate conditions of light, which strongly enhances ethylene synthesis. Both effects can be inhibited by the ethylene-perception blocking agent methylcyclopropene (MCP) or inhibitors of ethylene synthesis such as aminovinylglycine (AVG), indicating that light exerts its gravicompetence-generating effect via induced/enhanced ethylene synthesis. Gain in gravicompetence is accompanied by the induced/enhanced occurrence of calreticulin and lipoxygenase as detected by 2D-gels and Q-TOFF-analyses. Previously gravicompetent, light-grown coleoptile-less seedlings are characterized by gravi-incompetent growth during subsequent horizontal gravistimulation when perception of ethylene is inhibited by MCP. The results demonstrate that continuous perception of ethylene is an indispensable step, permanently required for the regulation of gravitropic growth in germinating primary shoots of rye, either within the process of graviperception and/or of the transduction of the gravi-signal.