AQUAPORIN-RELATED PROTEINS IN THE FILTER CHAMBER OF HOMOPTERAN INSECTS

In the Homopteran order of insects, the plant xylem feeders exhibit a highly differentiated part of their digestive tract known as the filte r chamber. In this tissue, water crosses plasma membranes through a tr ansepithelial osmotic gradient. In previous studies on the filter cham ber of Cicadella viridis, we purified and characterized from the plasm a membranes a 25 kDa protein that we demonstrated to be an aquaporin ( or water channel, member of the major intrinsic protein family, a grou p of membrane channels for small solutes). We called this protein AQPc ic for Cicadella aquaporin. In the present study, we used polyclonal a ntibody anti-AQPcic in Western blotting and immunocytochemical analysi s of the intestinal tract of Cercopis sanguinolenta, Philaenus spumari us, Aphrophora alni (Cercopidae), Euscelidius variegatus, and Scaphoid eus titanus (Jassidae). Western blotting experiments revealed that imm unologically related AQPcic proteins are found in those species. The m olecular weight of these proteins is 15-26 kDa. Immunocytochemical stu dies on ultrathin filter-chamber sections revealed that the anti-AQPci c antibody systematically labelled the membrane microvilli of epitheli al cells. A good correlation thus exists between the physiology of the se cells and the presence of aquaporin-related proteins in their membr anes.