Haemocytes play a commensal rôle in the synthesis of the dihydroxybenzoate required as a precursor for sclerotization of the egg case (ootheca) in the cockroach Periplaneta americana (L)

The secretions of the two colleterial glands give rise to the walls of the ootheca which, when hardened, serve to protect fertilised eggs in the cockroach P. americana. The larger left gland (LCG) secretes a β-D-glucoside of 3,4-dihydroxybenzoate, several proteins (oothecins), calcium oxalate crystals and a latent phenoloxidase enzyme. The smaller right gland (RCG) secretes a β-glucosidase. When the two secretions mix in the genital vestibulum, the glucoside is hydrolyzed to glucose and free dihydroxybenzoate, which is then oxidized by the phenoloxidase to the o-benzoquinone, which cross-links the oothecins Scanning and thin section electron microscopy (EM) showed haemocytes adhering to the LCG. The haemocytes were obtained by washing the gland with insect saline; and, when they were incubated with labelled tyrosine, they showed an enhanced ability to decarboxylate L-p-tyrosine to tyramine and then deaminate and oxidize tyramine to give p-hydroxyphenylacetate. After removal of adhering haemocytes, the LCG was no longer able to decarboxylate tyrosine. Injection of α-ecdysone into the abdomens of recently emerged adult females inhibited synthesis of a phenolic glucoside in the developing LCG but not of β-glucosidase produced by RCG. Furthermore, injecting inhibitors of the decarboxylase and monoamineoxidase enzymes partly closed down synthesis in vivo of the phenolic glucoside by LCG. Therefore, in the adult female cockroach, tyramine was converted to p-hydroxyphenylacetate in the haemocytes and then transferred to the gland where it was hydroxylated to 3,4-dihydroxyphenylacetate, which gave rise to a dihydroxybenzoate. Evidence suggested that biosynthesis of the oothecal sclerotizing agent could be controlled by juvenile hormone (JH) acting on the LCG or on haemocytes adhering to the gland.