Alkaline phosphatase activity in whitefly salivary glands and saliva

Alkaline phosphatase activity was histochemically localized in adult whiteflies (Bemisia tabaci B biotype, syn. B. argentifolii) with a chromogenic substrate (5-bromo-4-chloro-3-indolylphosphate) and a fluorogenic substrate (ELF-97). The greatest amount of staining was in the basal regions of adult salivary glands with additional activity traced into the connecting salivary ducts. Other tissues that had alkaline phosphatase activity were the accessory salivary glands, the midgut, the portion of the ovariole surrounding the terminal oocyte, and the colleterial gland. Whitefly nymphs had activity in salivary ducts, whereas activity was not detected in two aphid species (Rhodobium porosum and Aphis gossypii). Whitefly diet (15% sucrose) was collected from whitefly feeding chambers and found to have alkaline phosphatase activity, indicating the enzyme was secreted in saliva. Further studies with salivary alkaline phosphatase collected from diet indicated that the enzyme had a pH optimum of 10.4 and was inhibited by 1 mM cysteine and to a lesser extent 1 mM histidine. Dithiothreitol, inorganic phosphate, and ethylenediaminetetraacetic acid (EDTA) also inhibited activity, whereas levamisole only partially inhibited salivary alkaline phosphatase. The enzyme was heat tolerant and retained approximately 50% activity after a 1-h treatment at 65 degrees C. The amount of alkaline phosphatase activity secreted by whiteflies increased under conditions that stimulate increased feeding. These observations indicate alkaline phosphatase may play a role during whitefly feeding.