Regulation of Circadian Methyl Benzoate Emission in Diurnally and Nocturnally Emitting Plants

Abstract

Emission of methyl benzoate, one of the most abundant scent compounds of bee-pollinated snapdragon flowers, occurs in a rhythmic manner, with maximum emission during the day, and coincides with the foraging activity of bumblebees. Rhythmic emission of methyl benzoate displays a "free-running" cycle in the absence of environmental cues (in continuous dark or continuous light), indicating the circadian nature of diurnal rhythmicity. Methyl benzoate is produced in upper and lower snapdragon petal lobes by enzymatic methylation of benzoic acid in the reaction catalyzed by S -adenosyl-L -methionine:benzoic acid carboxyl methyltransferase (BAMT). When a detailed time-course analysis of BAMT activity in upper and lower petal lobes during a 48-hr period was performed, high BAMT activity was found at night as well as in continuous darkness, indicating that the BAMT activity is not an oscillation-determining factor. Analysis of the level of benzoic acid during a 24-hr period revealed oscillations in the amount of benzoic acid during the daily light/dark cycle that were retained in continuous darkness. These data clearly show that the total amount of substrate (benzoic acid) in the cell is involved in the regulation of the rhythmic emission of methyl benzoate. Our results also suggest that similar molecular mechanisms are involved in the regulation of methyl benzoate production in diurnally (snapdragon) and nocturnally (tobacco and petunia) emitting plants. INTRODUCTIONFlowers of many plant species attract pollinators by producing different complex mixtures of volatile compounds that give each species a unique and characteristic fragrance. Such volatile compounds emitted from flowers may function as both long-distance and short-distance attractants and play a prominent role in the localization and selection of flowers by insects, especially in moth-pollinated flowers, which are detected and visited at night (Dobson, 1994). Plants need to, and often do, vary the floral scent they emit during the life span of the flower, both in total output and in specific composition. These changes occur in relation to flower age (Tollsten, 1993;Pichersky et al., 1994;Wang et al., 1997; Dudareva et al., 1998Dudareva et al., , 2000, pollination status (Tollsten, 1993; Schiestl et al., 1997), environmental conditions (Jakobsen and Olsen, 1994), and diurnal endogenous rhythms (summarized by Dudareva et al., 1999). In addition to reduced costs for scent production, these intraspecific changes in floral fragrances also can influence the activity of flower visitors. For example, a quantitative and/or qualitative change of floral bouquets after pollination might lead to a lower attractiveness of these flowers and help to direct pollinators to the unpollinated flowers, thereby maximizing the reproductive success of the plant.It is an evolutionary advantage that plants have scent output at maximal levels only when potential pollinators are active. Plants that are pollinated by insects with maximum activity during the day (e.g., bees) show a diurnal...

The composition and timing of flower odour emission by wild Petunia axillaris coincide with the antennal perception and nocturnal activity of the pollinator Manduca sexta

“…and accessions. Rhythmic emissions of methyl benzoate, benzaldehyde, isoeugenol, benzeneacetaldehyde and benzyl benzoate have also been detected in Petunia hybrida (Kolosova et al 2001;Verdonk et al 2003;Negre et al 2003). The non-rhythmic emission of hexadecadienal methyl ester and Z-9,17-octadecadienol (Fig.…”

“…The production of flower volatiles restricted to the night could also be an adaptation of the plant to avoid seed predators, as was shown by Baldwin et al (1997) for N. attenuata. Antirrhinum flowers (Kolosova et al 2001), Artemisia annua (Lu et al 2002) and Rosa hybrida (Helsper et al 1998) also posses an internal clock controlling floral odour production, but they reach maximum levels during the day. We did not detect an endogenous circadian rhythm in the volatiles collected from P. integrifolia.…”

“…and accessions. Flower-odours of cultivated Petunia hybrida (cv Mitchell) have been collected in previous studies (Kolosova et al 2001;Verdonk et al 2003;Boatright et al 2004), but no information is available for the flower-odours of wild Petunia species, apart from our previous work on the differences between the odour blends of P. integrifolia inflata vs. P. axillaris parodii wild species (Stuurman et al 2004). We collected the odours of different accessions for both wild species to find out if they release similar flower-odour blends.…”

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

“…Numerous studies showed that terpenoid volatiles are mostly synthesized de novo in a few special physical structures, such as oil glands (Gershenzon et al 2000) and resin ducts (Miller et al 2005), which accumulate large quantities of terpenes. Biosynthesis occurs in the epidermal cells of plant tissues, through which they can easily be released into the atmosphere/rhizosphere (Kolosova et al 2001;Chen et al 2004;Tholl and Lee 2011). Several conifers accumulate significant amounts of scent oleoresins in their specialized needles, bark blisters or resin ducts and sapwoods (Zulak and Bohlmann 2010).…”

“…In Arabidopsis, mono-and sesquiterpene synthases are not expressed in flower petals, and their expression is restricted to nectaries, sepals, anthers and stigma (Tholl et al 2005). In the snapdragon flower, key volatile benzoid compounds, the monoterpene myrcene, (E)-β-ocimene biosynthesis and developmental regulation occur in the epidermal layer of the upper and lower lobes of petals, controlled by the circadian clock following the diurnal rhythm (Kolosova et al 2001;Muhlemann et al 2014). Similarly, H. coronarium promoters (PrHcTPS1 and PrHcTPS2) are involved in the temporal and spatial regulation of HcTPS genes associated with the biosynthesis of terpenoids (Li and Fan 2011;Li et al 2014).…”