Kolosova N, Sherman D, Karlson D, Dudareva N
Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907, USA.
Plant Physiol. 2001 Jul;126(3):956-64. doi: 10.1104/pp.126.3.956.
The benzenoid ester, methylbenzoate is one of the most abundant scent compounds 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:benzoic acid carboxyl methyltransferase (BAMT). To identify the location of methylbenzoate biosynthesis, we conducted an extensive immunolocalization study 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 extent, 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 BAMT protein detected in the outer epidermis and in the yellow hairs within the 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 biosynthesis. The concentration of scent production on flower surfaces that face the pollinators during landing may increase pollination efficiency and also help to minimize the biosynthetic cost of advertising for pollinators.
苯酯类化合物苯甲酸甲酯是在大多数金鱼草（Antirrhinum majus）品种中检测到的最丰富的气味化合物之一。它是在花瓣的上下裂片通过由S-腺苷-L-甲硫氨酸：苯甲酸羧基甲基转移酶（BAMT）催化的苯甲酸的酶促甲基化反应产生的。为了确定苯甲酸甲酯生物合成的位置，我们使用针对BAMT蛋白的抗体，在细胞和亚细胞水平上通过光学显微镜和电子显微镜进行了广泛的免疫定位研究。BAMT主要免疫定位在金鱼草花瓣裂片内表皮的锥形细胞中，在外表皮细胞中的定位程度要小得多。它也位于花冠管的内表皮中，在外表皮和蜜蜂通往花蜜途中管内的黄色绒毛中检测到很少的BAMT蛋白。这些结果强烈表明，气味生物合成基因几乎只在花器官的表皮细胞中表达。免疫金标记研究表明，BAMT是一种胞质酶，表明苯甲酸甲酯生物合成位于胞质中。在着陆过程中面向传粉者的花表面上的气味产生浓度可能会提高授粉效率，也有助于将向传粉者发出信号的生物合成成本降至最低。
