‘Osmotic pump‘ feeding by coreids |
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Authors: | P W Miles and G S Taylor |
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Institution: | (1) Department of Crop Protection, University of Adelaide, Waite Campus. Glen Osmond 5064, South Australia |
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Abstract: | 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. |
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Keywords: | Coreidae saliva osmotic pump phytotoxicoses sucrase |
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