Composition and variability of the saliva of coreids in relation to phytoxicoses and other aspects of the salivary physiology of phytophagous Heteroptera |
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Authors: | G S Taylor and P W Miles |
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Institution: | (1) Department of Crop Protection, University of Adelaide Waite Campus, 5064 Glen Osmond, South Australia |
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Abstract: | In the saciform, principal salivary glands ofMictis profana (Fabr.) (Coreidae: Heteroptera, Pentatomorpha), the contents of all lobes other than the posterior form gels consistent with
their contributing to the solidifying saliva (stylet sheath); the posterior lobe secretes most if not all of a sucrose-hydrolysing
enzyme that occurs in the nongelling (watery) saliva. Evidence for the occurrence of such an enzyme in the saliva of other
coreids is presented. That inM. profana has a pH optimum near neutral and a substrate specificity consistent with sucrase (sucrose α-D-glucohydrolase, EC 3.2.1.48)
as distinct from plant invertase (β-D-fruccofuranosidase, EC 3.2.1.26). Apart from some maltose-hydrolysing activity in the
salivary glands, also consistent with sucrase, no other carbohydrases and neither proteinase nor lipase were detected. Phosphatases
were found in gland extracts but not in secreted saliva. The saliva contains catechol oxidase (EC 1.10.3.1) from the accessory
gland and ducts. Topical application of pilocarpine caused individualM. profana to secrete up to 58 μl watery saliva which showed continuous and independent variation of sucrase activity (up to ca 0.012
Units/μl) and pH (6–8), although high sucrase content tended to coincide with high pH. Total protein varied up to 10 μg/μl,
and free amino acids up to 1.8 μg/μl leucine eq. Of the many proteins and/or protein subunits separable by electrophoresis
of gland contents and saliva, four had sucrase activity, the most mobile with MW ca 66 000. TLC indicatedinter alia phenyl alanine and tyrosine, but no DOPA nor other diphenolic substrates of the catechol oxidase in the watery saliva. The
soluble components of the saliva, which also has marked surfactant properties, are discussed in relation to the feeding process
of coreids and the characteristic lesions they produce in their food plants. |
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Keywords: | Coreidae Hemiptera phytotoxicoses saliva stylet sheath sucrase |
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