Stamen abscission and water balance in Metrosideros flowers

Cymules (3-flowered units borne on single pedicels:) were cut from inflores cences of Metrosideros collina J.R. & G. Forst. cv. Tahiti and used to test the effects of ethephon and ethylene on stamen abscission in the presence of silver thiosulphate (STS) and 1-methylcyclopropene (1-MCP), and to test the effects of holding solutions on cymule water balance and the progressio n of floral development. Flower bud and stamen abscission occurred in respo nse to 0.5-5.0 and 0.1 mu l l(-1) ethylene, respectively. Ethylene effects were partially negated by scrubbing exogenous ethylene, and more completely negated by STS (2.0 mM). 1-MCP caused greater ethylene production and inhi bited stamen abscission for only 1-2 days after treatment. Ethephon (10-100 00 mg l(-1)) induced stamen wilting rather than abscission, an effect that was not negated by STS. Stamen wilting was negatively correlated with stame n relative water content, and the increase in stamen wilting was generally reduced by treatments that enhanced cymule mass. Stamen wilting was least u sing a 100 g l(-1) sucrose pulse or holding solutions containing 30-40 g l( -1) sucrose, with hydroxyquinoline citrate (200 mg l(-1)) maintained at pH 5. Our results indicate that 1-MCP may be relatively ineffective in blockin g the effects of ethylene on the abscission of organs, such as the stamens of M. collina, which are highly sensitive to this hormone.