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Previous research into the genetic mechanisms of benzenoid and phenylpropanoid volatile biosynthesis has suggested the potential for metabolic flux, in which phenylalanine substrate dedicated to one pathway branch (i.e., benzenoid production) could alter volatile production in other pathways (i.e., phenylpropanoid production). However, little research has been conducted in planta to verify the validity of this hypothesis. We examined the emission rates of representative benzenoid and phenylpropanoid volatiles from seven cultivars of Phlox subulata L. to determine if cultivars had metabolic flux differences in terms of these two compound categories. Cultivars that produced large quantities of methyl benzoate and benzaldehyde were found to emit little or no phenylacetaldehyde and 2-phenylethanol, and vice versa. These results suggest that P. subulata cultivars experience phenylalanine substrate flux directed toward one pathway and away from the alternate branch. Such a pattern may be the result of differential selection pressures, in which gene expression has been altered to direct flux away from either benzenoid or phenylpropanoid production. Moreover, if these patterns hold true in wild populations, metabolic flux may lead to differential pollinator behavior and further phenotypic evolution. Future research using molecular tools could verify the role of metabolic flux in determining scent phenotypes and pinpoint the exact nature of the genetic mutations leading to phenotypic differences in odor. |
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