Emission of Volatiles From Brown Boronia Flowers: Some Comparative Observations

Extensive research has focused on the concentration of aglycones within brown boronia (Boronia megastigma) flowers, however emission of volatiles into the headspace above these flowers is not well documented. Using solid-phase microextraction (SPME) to trap volatiles and GCMS analysis, we observed 23 volatiles in the headspace above buds and flowers throughout flower maturation, above dissected floral organs and above whole plants held for 36 h under either continuous light, continuous dark or 12 h light: 12 h dark: 12 h light treatments. Fully-opened flowers emitted the most complex mixture of volatiles and in the greatest quantity, with a rapid decline in senescent flowers. Caryophyllene, humulene and bicyclogermacrene declined as flower buds matured; β-ionone increased. From the individual floral organs, emission from the petaline anthers comprised 38% of total emissions from the (calculated) 'whole flower', with 27% contributed by the petals and 10·5% by the stigma. Monoterpenes dominated the headspace from the calyx; dodecyl acetate, methyl jasmonate and (Z)-n-heptadec-8-ene were relatively predominant in emissions from the androecium. β-Ionone, the major floral volatile in brown boronia, dominated volatiles emitted from the stigma (87%). However, the relatively tiny petaline anthers, active in pollen production and high in carotenoids, contributed the greatest overall amount of β-ionone to emission from the whole flower. There were three different patterns in emission of volatiles from plants in response to different light conditions: (1) emission patterns identical irrespective of light environment, with maximum emission in the 'endogenous' dark period, i.e. when the plant would normally have been in the dark (α-pinene); (2) similar emission in all treatments, with an increase and decline over a period of 26 h (5-acetoxy linalool, cyclic β-ionone, dodecyl acetate and (Z)-n-heptadec-8-ene); and (3) emission in all treatments but enhanced in the dark, with a 27·5 h period in some cases (cyclic β-ionone endoperoxide, dihydro β-ionone, β-ionone, and 'total volatiles'). Preliminary evidence is presented for endogenous control of emission of a number of volatiles such as α-pinene, with perhaps diurnal control of others such as β-ionone. (C) 2000 Annals of Botany Company.