ASGSB 1999 Annual Meeting Abstracts

THE ROLE OF ETHYLENE IN SEED DEVELOPMENT IN BRASSICACEAE. G. McClure, K. Ramonell and M. Musgrave; Department of Plant Pathology & Crop Physiology, Louisiana State University, Baton Rouge, LA.

The role of ethylene in seed development was investigated in the gas spaces inside siliques of Brassica rapa (L.) and Arabidopsis thaliana (L.) Heynh cv. Columbia.  Brassica ethylene production in the stem and beak segments of developing siliques was quantified 3-14 days after pollination (DAP) using gas chromatography.  Ethylene concentration peaked at 10 ppm on 8 DAP for both stem and beak then decreased to a steady state of 3 ppm as the silique matured. Growth in low oxygen (<50 mmol/mol) was found to prevent seed development in Arabidopsis, and no ethylene was measured in these empty siliques. To understand why ethylene is absent under these conditions, mRNA levels of ACC oxidase and ACC synthase genes were monitored using ribonuclease protection assays, and tissue-specific expression of the biosynthetic enzymes was analyzed by in situ hybridization.  ACC synthase expression in siliques was unchanged with decreased O₂ concentration, while expression of ACC oxidase increased sharply at O₂ concentrations that prevented ethylene production.  The tissue-specific patterning of expression for both genes shifted from the developing embryo to the silique wall as low O₂ inhibited embryo development. Experiments are currently underway to determine if seed development in these species is absolutely dependent on high ethylene concentrations in the silique microenvironment.

 (Supported by NASA: NAG5-3756, NAG-100139, and NGT-40039.)

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