Evening specific oscillations of scent emission, SAMT enzyme activity, and SAMT mRNA in flowers of Stephanotis floribunda

Stephanotis floribunda (Asclepediaceae), a plant that grows in Madagascar and is now a common house plant, emits a number of volatiles from its flowers. Its floral scent has been noted to increase in intensity during the night. At this time prominent scent compounds include benzyl alcohol, benzyl acetate, benzyl benzoate, eugenol, α-farnesene, linalool, linalool oxide, methyl benzoate (MBA), methyl salicylate (MSA), β-ocimene, phenylethyl alcohol, and 1-nitro-2-phenylethane. To investigate the level(s) at which the variation in fragrance emission is controlled, we isolated a gene encoding the enzyme salicylic acid carboxyl methyltransferase (SAMT), which catalyses the synthesis of methyl salicylate from salicylic acid and S-adenosyl-L-methionine. The expression of SAMT is petalspecific and developmentally regulated. Under light/dark conditions, SAMT mRNA levels and SAMT enzyme activities oscillate and reach the maxima in the first half of the night. These patterns correlate well with the emission of MSA. We conclude that the daily fluctuation in emission of MSA in S. floribunda likely involves de novo volatile synthesis resulting from time-regulated SAMT mRNA accumulation and SAMT enzyme activity.