Ultrastructural detection of lipids in the cephalic salivary glands of Apis mellifera and Scaptotrigona postica (Hymenoptera: Apidae) workers

ABSTRACT Secretory cells of the cephalic salivary glands (CSGs) of eusocial bees produce and accumulate lipid-like secretion in the lumens of their alveoli. Correspondingly, secretory cells present typical ultrastructural features of lipid-compound producers. Previous work on bees has revealed inter-specific differences in the chemical composition of secretion, and the production mechanisms and secretory cycle of secretory cells. In this work a comparative analysis of the mechanisms of lipid storage in the CSGs of Apis mellifera (Linnaeus, 1758) and Scaptotrigona postica (Latreille, 1807) workers was carried out. The ultrastructural location of lipids was ascertained using imidazole-osmium (IO), using individuals in different stages of their life cycles. Lipid deposits were identified inside glandular cells and in the alveolar lumens in all individuals, but differences were observed between the species. The glandular cells of A. mellifera workers presented positive reactions to IO as droplets dispersed in the cytoplasm, as vesicles and in the channels formed by apical plasma membrane infolds. In S. postica , lipid compounds were detected inside the mitochondrial matrix and in smooth endoplasmic reticulum cisterns. In both species, forager workers exhibited the largest amounts of lipids stored in the alveolar lumen. The differences between the species are discussed, taking into account specific behavioral differences.

摘要：真社会性蜜蜂的头唾液腺（cephalic salivary glands, CSGs）分泌细胞可在其腺泡管腔内合成并积累脂样分泌物，此类分泌细胞具备脂类合成细胞典型的超微结构特征。过往针对蜜蜂的研究已揭示，其分泌物的化学成分、分泌细胞的合成机制与分泌周期均存在种间差异。本研究针对西方蜜蜂（Apis mellifera, Linnaeus, 1758）与波氏刺舌蜂（Scaptotrigona postica, Latreille, 1807）的工蜂头唾液腺内的脂类储存机制开展了比较分析，采用咪唑-锇酸染色法（imidazole-osmium, IO），结合不同生命周期阶段的个体，确定脂类的超微结构定位。结果显示，所有个体的腺细胞内与腺泡管腔中均检测到脂类沉积，但两个物种间存在差异：西方蜜蜂工蜂的腺细胞对咪唑-锇酸染色呈阳性反应，脂类以液滴形式分散于细胞质、囊泡及顶质膜内褶形成的通道中；而波氏刺舌蜂的脂类化合物则在线粒体基质与滑面内质网潴泡内被检测到。两个物种的采集工蜂腺泡管腔内储存的脂类含量均为最高。本研究结合两个物种的特异性行为差异，对其脂类储存机制的种间差异展开了讨论。