Role of ethylene in cotyledon development of microspore-derived embryos ofBrassica napus

Ethylene production during seed development in Brassica napus occurs first at 20 d after pollination (DAP), while a second greater peak occurs at 35 D AP. Because of the inaccessible location of the embryo within the maternal tissue, microspore-derived embryos (MDEs) of B. napus were used as a model for studying the role of ethylene during embryo development. The MDEs also produced a peak in ethylene evolution at 20 DAC (i.e. the early cotyledonar y stage), dropping to minimal levels by 25-30 DAC. At 20 DAC the excised co tyledon evolved 85% of the ethylene found in the whole MDE. To determine th e role of ethylene, MDEs were treated with aminoethoxyvinylglycine (AVG, an inhibitor of ethylene biosynthesis), CoCl2 (an inhibitor of 1-aminocyclopr opane-1-carboxylic acid (ACC) oxidase), and silver thiosulphate (STS, an in hibitor of ethylene action). An inhibition in ethylene production or action at 20 DAC resulted in diminished lateral cotyledon expansion, due to a red uction in the lateral expansion of cells within the cotyledon. Recovery to 'control-type' fevers of cotyledon cell expansion was achieved by applicati on of ACC (the metabolic precursor of ethylene) to AVG-treated MDEs. Thus, ethylene production at 20 DAP likely controls cotyledon expansion during em bryo development.