ABSTRACT
Saliva is important in the interaction of many insect species and their plant hosts. The composition and function of aphid saliva was until yet the subject of more than 100 research articles. While early studies used enzymatic assays to determine enzyme activity, recently published studies use proteomic approaches, in planta protein expression and RNA interference to study the function of salivary proteins. The primary components of aphid saliva originate in the salivary glands, a pair of organs located in the dorsal metathorax (Ponsen 1972). Each half of the salivary gland pair consists of two components, a large principal gland that is often bilobed and a smaller accessory gland. The two subunits join in the salivary canal that leads to the stylet tips, where it unites with the nutrition channel to form the so called common duct (Uzest et al. 2010). The principal gland is innervated by nerves and includes eight secretory cells, whereas the accessory gland is not innervated and the cells show no differentiation. The contribution of the two subunits to the saliva has been suggested largely through plant virus transmission studies (Gray and Gildow 2003). Persistent and circulative viruses that infect the phloem are transferred from the aphid hemolymph into saliva through the accessory gland, indicating that this structure might be responsible for the production of some watery saliva. Hints exist that different salivary glands produce specifi c proteins, demonstrated in Schizaphis graminum by the use of an antibody against a 154 kDa protein (Cherqui and Tjallingii 2000), and in more detail that different subsets of secretory cells produce different proteins, observed in principal salivary glands of Acyrthosiphon pisum for the effectors C002
Institute for Insect Biotechnology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, 35394 Giessen, Germany.
