Cellular and subcellular localization of S-adenosyl-L-methionine: Benzoic acid carboxyl methyltransferase, the enzyme responsible for biosynthesis ofthe volatile ester methylbenzoate in snapdragon flowers
N. Kolosova et al., Cellular and subcellular localization of S-adenosyl-L-methionine: Benzoic acid carboxyl methyltransferase, the enzyme responsible for biosynthesis ofthe volatile ester methylbenzoate in snapdragon flowers, PLANT PHYSL, 126(3), 2001, pp. 956-964
The benzenoid ester, methylbenzoate is one of the most abundant scent compo
unds detected in the majority of snapdragon (Antirrhinum majus) varieties.
It is produced. in upper and lower lobes of petals by enzymatic methylation
of benzoic acid in the reaction catalyzed by S-adenosyl-L-methionine :benz
oic acid carboxyl methyltransferase (BAMT). To identify the location of met
hylbenzoate biosynthesis, we conducted an extensive immunolocalization stud
y by Light and electron microscopy at cellular and subcellular levels using
antibodies against BAMT protein. BAMT was immunolocalized predominantly in
the conical cells of the inner epidermal layer and, to a much lesser exten
t, in the cells of the outer epidermis of snapdragon flower petal lobes. It
was also located in the inner epidermis of the corolla tube with little BA
MT protein detected in the outer epidermis and in the yellow hairs within t
he tube on the bee's way to the nectar. These results strongly suggest that
scent biosynthetic genes are expressed almost exclusively in the epidermal
cells of floral organs. Immunogold labeling studies reveal that BAMT is a
cytosolic enzyme, suggesting cytosolic location of methylbenzoate biosynthe
sis. The concentration of scent production on flower surfaces that face the
pollinators during landing may increase pollination efficiency and also he
lp to minimize the biosynthetic cost of advertising for pollinators.