Floral Scent Production in Clarkia (Onagraceae) (I. Localization and Developmental Modulation of Monoterpene Emission and Linalool Synthase Activity)

Abstract

The flowers of many plants emit volatile compounds as a means of attracting pollinators. We have previously shown that the strong, sweet fragrance of CIarkia breweri (Onagraceae), an annual plant native to California, consists of approximately 8 to 12 volatile compounds-three monoterpenes and nine benzoate derivatives (R.A. Raguso and E. Pichersky [1994] Plant Syst Evol [in press]). Here we report that the monoterpene alcohol linalool is synthesized and emitted mostly by petals but to a lesser extent also by the pistil and stamens. Two linalool oxides are produced and emitted almost exclusively by the pistil. These three monoterpenes are first discernible in mature unopened buds, and their tissue levels are highest during the first 2 to 3 d after anthesis. levels of emission by the different floral parts throughout the life span of the flower were correlated with levels of these monoterpenes in the respective tissues, suggesting that these monoterpenes are emitted soon after their synthesis. Activity of linalool synthase, an enzyme that converts the ubiquitous CIO isoprenoid intermediate geranyl pyrophosphate to linalool, was highest in petals, the organ that emits most of the linalool. However, linalool synthase activity on a fresh weight basis was highest in stigma and style (i.e. the pistil). Most of the linalool produced in the pistil is apparently converted into linalool oxides. lower levels (0.1%) of monoterpene emission and linalool synthase activity are found in the stigma of Clarkia concha, a nonscented relative of C. breweri, suggesting that monoterpenes may have other functions in the flower in addition to attracting pollinators. ~ Flowers of many plants attract pollinators by producing and emitting volatile compounds. The scent emitted by such flowers is often a complex mixture of low mol wt compounds, and the relative abundances and interactions of the constituents give the flower its particular characteristic fragrance. Floral scents have been demonstrated to function as longand short-distance attractants and nectar guides to a variety '

Developmental Regulation of Monoterpene Biosynthesis in the Glandular Trichomes of Peppermint

“…The close correspondence between in vitro enzyme activity and the rate of monoterpene biosynthesis measured in vivo suggests that monoterpene formation in peppermint oil gland cells is tightly controlled by the levels of biosynthetic enzymes. Similar correlations have been noted for the formation of a variety of isoprenoids during flower (Pichersky et al, 1994), leaf (Croteau et al, 1981), and seedling (Green and Baisted, 1972) development, and after induction by pathogens (Dudley et al, 1986;Hanley et al, 1992), but this is the first time that a related array of isoprenoid biosynthetic enzymes has been investigated in a single specialized cell type.…”

Floral Scent Production in Clarkia breweri (Onagraceae) (II. Localization and Developmental Modulation of the Enzyme S-Adenosyl-L-Methionine:(Iso)Eugenol O-Methyltransferase and Phenylpropanoid Emission)

“…These results are very similar to those obtained for LIS, an enzyme that produces linalool, another floral scent compound in C. breweri. We observed strong positive correlation between levels of LIS enzyme activity, protein, and mRNA at the site of synthesis and emission of linalool in the flower (Pichersky et al, 1994;Dudareva et al, 1996).…”

“…The strong, sweet fragrance of C. breweri consists of 8 to 12 different volatiles that fall into two groups: monoterpenoids and phenylpropanoids-benzenoids (Raguso and Pichersky, 1995). We have shown that linalool, an acyclic monoterpene, is synthesized in C. breweri petals and other floral tissues in a reaction catalyzed by LIS (Pichersky et al, 1994(Pichersky et al, , 1995, and that the enzyme activity is regulated at a pretranslational level (Dudareva et al, 1996). A closely related species, Clarkia concinna (from which C. breweri is believed to have evolved [Raguso and Pichersky, 1995]), also possesses the gene encoding LIS, but the expression of this gene in this nonscented species is limited to the stigma, and the level of expression is much lower than in the stigma of C. breweri.…”

Characterization of an Acyltransferase Capable of Synthesizing Benzylbenzoate and Other Volatile Esters in Flowers and Damaged Leaves of Clarkia breweri

“…6A). Day 2 of anthesis is the day in which the stigma opens up and becomes receptive, a process that involves rapid cell expansion and consequently a reduction in protein content per cell (Pichersky et al, 1994). However, even when BEBT activity levels and BEBT protein levels are plotted after normalization to protein content (data not shown), a substantial drop of 50% in both is still observed from d 1 to 2.…”