Acid phosphatases in the haemolymph of the desert locust, Schistocerca gregaria, infected with the entomopathogenic fungus Metarhizium anisopliae

A comparison has been made between the effects of wounding, chemical stimul ation of the immune system and fungal infection on acid phosphatase (AcP) a ctivity in the haemolymph of the desert locust, Schistocerca gregaria, Untr eated control locusts had constitutive levels of AcP. As a lysosomal enzyme , AcP may have a role in autophagy and cell turn over as well as defence. I njection of saline and beta-1,3-glucan caused significant increases in haem ocyte and plasma AcP. AcP activity also increased in the haemolymph on the 3rd day after inoculation with the entomopathogenic fungus M. anisopliae va r acridum. This coincided with a decline in the total haemocyte count and a marked reduction in the proportion of plasmatocytes and coagulocytes that stained positive for AcP. Therefore a priori it seemed unlikely that the ex tra AcP in infected insects came from the host. A fungal origin for the enz yme was suggested by the identification of AcP isoforms from haemolymph of different treatments. Control inoculated toil only) insects had an AcP at a pi of 4.3 that was stimulated further by the injection of laminarin. Addit ional isoforms appeared at around 7.3-7.5 in the laminarin treatment. Howev er, the 4.3 isoform appeared to be suppressed in the insects infected with M. anisopliae var acridum. The band intensity was more like that of the con trol than the laminarin-injected insects. Two new isoforms appeared later o n in infection. These enzymes had pIs that corresponded to some of the AcPs produced in vitro by the fungus. The results are discussed in the light of the possible benefits of secreted fungal acid phosphatases to the pathogen . (C) 2000 Elsevier Science Ltd. All rights reserved.