Lars Tollsten

Floral scents—a checklist of volatile compounds isolated by head-space techniques

Abstract A checklist is presented of floral scent compounds retrieved by head-space techniques and separated and identified mainly by gas chromatography and mass spectrometry. The checklist is based on reports presented in 118 original articles between the years 1966 and 1992. The emphasis in our discussion is on comparison of identified chemical substances as a basis for studies of pollination attractants. Isolation techniques, systematic implications of floral scents and structure-activity relationships are briefly discussed. In all over 700 identified compounds are listed from 441 taxa in 174 genera in 60 families of plants. They mainly represent fatty acid derivatives, benzenoids, phenylpropanoids, isoprenoids, nitrogen- and sulphur-containing compounds.

Headspace volatiles of whole plants and macerated plant parts of Brassica and Sinapis

Headspace volatiles collected from six Crucifer species of the two genera Brassica and Sinapis were investigated by GC/MS. A total of 34 compounds were identified from both whole plants and macerated plant parts. Typical cell-degradation compounds including alcohols, aldehydes and glucosinolate breakdown products were primarily found in macerate samples, while terpenes were detected almost exclusively in whole plants. Macerated buds generally contained higher amounts of nitriles and isothiocyanates than did macerated leaves. Several compounds here identified have, to our knowledge, not been previously reported in Brassica and Sinapis.

Floral scent chemistry and pollination ecology in phytelephantoid palms (Arecaceae).

The subfamilyPhytelephantoideae comprises three genera (Ammandra, Aphandra, andPhytelephas) and seven species of dioecious palms. The floral scents ofAmmandra dasyneura, A. decasperma, Aphandra natalia, Phytelephas aequatorialis, P. macrocarpa, andP. seemannii were analyzed by gas chromatography-mass spectrometry. We studied the pollination biology ofA. natalia, P. aequatorialis, andP. macrocarpa, and tested how the synthetically produced main constituents of the floral scents ofAphandra andPhytelephas attracted insects in two natural populations ofPhytelephas. The genera are distinct in terms of floral scents.Ammandra has sesquiterpenes,Aphandra (+)-2-methoxy-3-sec-butylpyrazine, andPhytelephas p-methyl anisol. These constituents dominated the scents quantitatively and qualitatively. The similarity between scents of male and female inflorescences was 76.5% inAmmandra, 84.2% inAphandra, and >99% inPhytelephas. Different species ofAleocharinae (Staphylinidae) pollinateAphandra natalia andPhytelephas species and reproduce in their male inflorescences.Derelomini (Curculinoidae) andMystrops (Nitidulidae) only visit and pollinatePhytelephas in which male inflorescences they reproduce. A species ofBaridinae (Curculionidae) only visits and pollinatesAphandra natalia, and reproduces in its female inflorescence. The apparent reliance on one or a few floral scent constituents as attractants and few and specific pollinators may indicate co-evolution. Sympatric species ofPhytelephantoideae have different scents. We suggest that species with similar scents have allopatric distributions due to the absence of a pollinator isolation mechanism.

Volatiles emitted by apple fruitlets infested by larvae of the European apple sawfly

Abstract The effect of infestation by larvae of the European apple sawfly ( Hoplocampa testudinea ) on the emission of volatiles from apple fruitlets was investigated. Healthy apples emitted a blend of terpenoids and a few aromatic and short aliphatic compounds. Infested apples emitted the same compounds as healthy apples. However, trans , trans - α -farnesene, trans - β -ocimene and another terpenoid were emitted in significantly larger amounts, whereas the other volatiles showed no quantitative change. The results were obtained with picked apples and could be confirmed in the field with single apples left on the tree. Several non-terpenoid volatiles emanated from the frass and from epidermal glands of the sawfly larvae. The possible ecological significance of the increased emission of terpenoids by infested apples is discussed with reference to a parasitic wasp that attacks the sawfly larvae.

Volatile organic compounds emitted from beech leaves

Abstract Volatile organic compounds (VOC) from beech ( Fagus sylvatica ) leaves have been studied. Headspace samples were collected in the forest from leaves in situ , and were analysed by GC-mass spectrometry. The major volatile constituent was sabinene accompanied by other isoprenoids as well as by (Z)-3-hexenyl acetate and (Z)-3-hexenol. Average emissions of 0.28 μg (g leaf dry wt hr) −1 , being equivalent to 84 μg (m 2 hr) −1 , were found in the beech forests studied. These figures indicate about one to two orders of magnitude lower emissions from beech, compared to needle-bearing trees and isoprene-producing broadleaf species. The variation in emissions was explored using multivariate methods, and was found to be clearly correlated to ambient temperature.

Floral scent in dioeciousSalix (Salicaceae)—a cue determining the pollination system?

Floral scents of male and female inflorescences of three dioeciousSalix species were collected by head-space adsorption, and analysed by GC-MS. InSalix caprea andS. cinerea 1,4-dimethoxy benzene was the main compound, and male and female scents showed a high degree of resemblance. No dominant compound was found inS. repens and malefemale scent similarity was low. Floral scent inSalix is likely a strong orientation cue, guiding pollinators between male and female plants ensuring pollen transfer and pollination. We suggest that a high degree of male-female floral scent resemblance is coupled to a high degree of insect pollination. Floral scent does not promote reproductive isolation betweenS. caprea andS. cinerea.

Floral scent and intrafloral scent differentiation in Moneses and Pyrola (Pyrolaceae)

Floral scent was collected by headspace methods from intact flowers, petals, and stamens of four species ofPyrolaceae. The scent samples were analyzed by coupled gas chromatography-mass spectrometry (GC-MS). The floral scent inPyrola spp. is differentiated into a characteristic petal scent—phenyl propanoids and a characteristic stamen scent—methoxy benzenes. InMoneses the scent is characterized by isoprenoids and benzenoids, with a larger proportion of benzenoids in the stamens compared to the petals. Specific anther scents may promote foraging efficiency in buzz-pollinated species and enhance flower fidelity. Variation in floral scent composition is consistent with the taxonomic relationships among the genera and species examined.

Floral scent in generalistic Angelica (Apiaceae)—an adaptive character?

Abstract The floral scent of three taxa of Angelica was dominated by monoterpenes and benzenoids. Scent of A. archangelica ssp. litoralis and A. silvestris both contain considerable amounts of α-pinene and 2-hydroxybenzaldehyde, the former also having linalool and the latter myrcene and limonene in large amounts. In the scent of A. archangelica ssp. archangelica cis- and trans -β-ocimene are dominating. There is a considerable within species variation in these, and other compounds. The pattern of scent compounds found in Angelica is general in some aspects and more specific in others. The volatile compounds found in Angelica are found also in many other flowering plants showing various degrees of specialization in pollination biology. The chemical composition of the floral scent of the three taxa of Angelica conforms with the current delimitation of the taxa.