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Flower Power: Floral Scent Profiles of Buddleia Varieties Vary for Pollinators
source:separationsnow.com     author:     2012-10-10

Scents for life
Floral scents are the lifeblood of many flowers. They have evolved to attract suitable pollinators, whether they are bees, butterflies or flies. The common Buddleia variety, Buddleia davidii, is a prime example of this. Its strong scent is so irresistible to butterflies that it is known far and wide as the butterfly bush.
However, other varieties of Buddleia have quite different flower shapes and scents to B. davidii and are attractive to different types of pollinators like bees and flies. The floral characteristics of particular species are thought to have evolved to attract the indigenous pollinators, along with the flower colour and shape and the nectar.
Within the Buddleia family, the floral aromas of only three species have been studied to try and find which particular compounds in the scent are the principle attractants. They are the common B. davidii, B. yunnanensis and B. officinalis. Now, scientists have examined more species to see if there are any similarities in the scent compositions and how they relate to the pollinators that they are trying to attract.

SUN Weibang and colleagues from Kunming Botanical Garden, Kunming Institute of Botany, and Bruce Dunn from Oklahoma State University, Stillwater, OK, selected four varieties which are native to four different continents and collected their scents for a GC/MS analysis.

Four floral Buddleia species

B. lindleyana is found in the wild in China. It has abundant blue or purple flowers and is pollinated by butterflies. The three remaining varieties were sampled in Kunming Botanical Garden, although they are endemic to other countries. B. cordata is found in Mexico and its white, cream or yellow flowers turn orange with age and attract a range of small bees and flies and some butterflies.

B. loricata is native to Lesotho and Transkei in southern Africa. It has highly aromatic white, cream or pale yellow flowers which smell like honey and attract butterflies and flies in the botanical garden. B. tubiflora is found in South America and has bright orange-tipped florets but no scent. It is pollinated by hummingbirds which feed on the nectar within the flower heads.

Freshly blooming flowers from each plant were enclosed in plastic bags and the volatile compounds issuing from the flowers were drawn into adsorbent cartridges. After their elution, they were identified by GC/MS with electron ionisation, using a standard 5% phenyl methylpolysiloxane column. The individual compounds were characterised from the retention times and retention indices and their mass spectra.

Scent profiles differ between varieties
No volatile compounds were detected from the flowers of B. tubiflora and the researchers could not detect any scent. This agrees with the widely held belief that flowers which are pollinated by hummingbirds are scentless.

A total of 50 compounds were identified from the three remaining Buddleia species but there was very little overlap between them, with only linalool and alpha-farnesene found in all three. The main classes of compounds found were terpenoids, fatty acid alcohols, ketones, aldehydes, hydrocarbons and benzenoids.

4-Oxoisophorone, alpha-farnesene and linalool were the three most abundant volatiles in the scent of B. loricata. The first two are known to generate strong antennal responses from butterflies and linalool is also emitted from other plants that attract butterflies. This is consistent with the observation that butterflies were regular visitors to the plant in the botanical gardens, although flies were also attracted. The researchers declared that the relative importance of each group should be studied in future work.

In contrast, beta-caryophyllene, alpha-farnesene and 1-octen-3-ol were the principal compounds emitted from B. lindleyana flowers, which also attract butterflies. The contrasting compositions of B. loricata and B. lindleyana suggested that the plants use different mechanisms to attract their pollinators.

Monoterpenes dominated the scent of B. cordata, principally trans-beta-ocimene which is present in many floral scents that attract bees and small flies. This is consistent with the observation that bees visited the plants in the botanical gardens.

Given that the floral scent profiles are markedly different, SUN Weibang suggested that they might have “evolved in conjunction with the sensory capabilities of different visitors as a specific group of pollinators.” He added that more Buddleia species should be examined to provide a broader bank of data which could be used in further studies of pollination signals and to breed new odour varieties by hybridisation.

(Source: http://www.separationsnow.com, Author: Steve Down)

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