PHENOTYPIC PLASTICITY OF STEM ELONGATION IN 2 ECOTYPES OF STELLARIA-LONGIPES - THE ROLE OF ETHYLENE AND RESPONSE TO WIND

Using two ecotypes of Stellaria longipes, an alpine form with low plas ticity and a prairie form with high plasticity, we investigated whethe r ethylene was involved in the response to wind stress and might be im portant in controlling plasticity of stem elongation. Stem growth inhi bition was positively correlated with concentration of ethephon applic ation and elevation in ambient ethylene in alpine ecotypes, whereas st em growth in prairie plants was stimulated by low ethephon concentrati ons. When treated with high AVG, the effects were reversed: alpine pla nt growth was promoted and prairie plant growth was inhibited. Prairie plants exhibited a daily rhythm in ethylene evolution which increased and peaked at 1500h, and which was absent in alpine plants. Ethylene evolution did not change significantly during the first 2 weeks of gro wth in alpine plants, whereas ethylene in prairie plants increased sig nificantly during periods of rapid stem elongation. Wind treatment inh ibited growth in both ecotypes, but only alpine plants showed a recove ry of growth to control levels when wind stressed plants were pretreat ed with STS. In addition, only alpine plants showed an increase in eth ylene evolution in response to wind simulation, whereas prairie plant ethylene evolution did not deviate from rhythms observed in unstressed plants. We concluded that ethylene dwarfs stems in alpine S. longipes in response to wind stress. However, low levels of ethylene may stimu late growth in prairie ecotypes and act independently of wind stress i ntensity. The contrasting ability to synthesize and respond to ethylen e can account for part of the difference in plasticity documented betw een the two ecotypes.