Thursday, August 9, 2007

PS 61-94: Is there a tradeoff between drought avoidance and drought tolerance?

Amanda R. Shores and Susan C. Lambrecht. San Jose State University

Many plant species exhibit flower color polymorphisms in which individual plants have either colored or white flowers.  White-flowered morphs often lack anthocyanin pigments that promote drought tolerance.  We were interested in whether different colored morphs would be associated with different drought coping strategies.  Specifically, we questioned whether a morph with a lower drought tolerance (assessed via water-use efficiency) would flower earlier in order to avoid the drought season.  We used an annual species, Leptosiphon bicolor (Polemoniaceae) that has a flower color polymorphism to explore this idea.  We conducted a greenhouse study on L. bicolor in which we measured a variety of physiological traits on both pink- and white-flowered plants, including photosynthesis, transpiration, stomatal conductance, and days to flower. Presence of anthocyanin was determined through thin layer chromatography and spectrophotometry analyses.  We also used stable carbon isotope ratios (δ13C) to infer long-term water-use efficiency. T-tests were performed on each of the measured variables comparing plants with white and pink flowers (δ13C P = 0.37, stomatal conductance P = 0.17, photosynthesis P = 0.86, transpiration P=0.24, days to flower P = 0.40). From the chromatography and spectrophotometry analyses, we saw no differences in the pigments of the leaf/stem material between the morphs of L. bicolor.  These results showed that no tested variable was related to the flower color polymorphism in L. bicolor. Therefore, we found no differences between the drought-coping strategies of the two color morphs.

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