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Species of Coreidae (Heteroptera) cause ‘water soaked’ lesions in their food plants. Such insects typically feed from parenchyma
in and surrounding vascular tissues and also cause acropetal wilting and necrosis of small diameter shoots. Feeding byMictis profana (Fabr.) in South Australia on the shoots ofAcacia iteaphylla F. Muell. ex Benth. was found to cause a local, concurrent increase in both water content and free amino acid concentration,
consistent with phloem unloading. Coreids, unlike other groups of phytophagous Heteroptera, secrete a salivary sucrase (α-D-glucohydrolase,
EC 3.2.1.48) as probably the sole salivary carbohydrase, and tissues attacked byM. profana showed more sucrose hydrolysing activity than unattacked. The salivary enzyme is postulated to cause unloading of solutes
into the apoplast due to the osmotic effects of conversion of endogenous sucrose to glucose and fructose, allowing the insect
to suck the leaked contents of many cells from a single locus. The term ‘osmotic pump feeding’ is proposed for such a process.
In demonstrations of its feasibility, infiltration of shoots with mixtures of glucose and fructose stoichiometrically equivalent
to isosmotic sucrose increased the amounts of tissue sap and amino acid that could be sucked from the tissues; similarly,
invertase and 1 M sugars forced into the extracellular space of stem sections increased the amino acids offloaded into the
bathing solutions. 相似文献
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Comparison of damage to Eucalyptus caused by Amorbus obscuricornis and Gelonus tasmanicus 总被引:1,自引:0,他引:1
M. J. Steinbauer G. S. Taylor J. L. Madden 《Entomologia Experimentalis et Applicata》1997,82(2):175-180
Amorbus obscuricornis (Westwood) and Gelonus tasmanicus (Le Guillou) (Heteroptera: Coreidae) are specific to Eucalyptus (Myrtaceae). A. obscuricornis feeds almost exclusively upon apical shoots and causes a characteristic wilting and necrosis. By comparison, the feeding activities of G. tasmanicus result in no obvious phytotoxicosis. Salivary gland extracts from both species exhibited sucrase activity but no pectinmethylesterase (PME) activity. Saliva from A. obscuricornis also exhibited considerable oxidase activity. Sucrase activity was significantly higher in extracts derived from G. tasmanicus than from A. obscuricornis, but this could not explain the observed differences in phytotoxic symptoms. It is suggested that differences in plant damage are attributable to the site of feeding activity (i.e. young versus mature tissue), which predetermines the reactivity of host tissues, and/or the quantity of salivary enzymes injected. 相似文献
3.
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. 相似文献
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