Pearl bodies are small (0.5 - 3.0 mm), lustrous, pearl-like food bodies produced from the epidermis of leaves, petioles and shoots of certain plants. They are rich inlipids,proteins andcarbohydrates, and are sought after by various arthropods and ants, that carry out vigorous protection of the plant against herbivores, thus functioning as a biotic defence. They are globose or club-shaped on short peduncles, easily detached from the plant, and are food sources in the same sense asBeltian bodies, Müllerian bodies, Beccarian bodies,coccid secretions andnectaries.[1] They occur in at least 19 plant families (1982) with tropical and subtropical distribution.[2]
Cells or tissues that offer food rewards to arthropods are commonplace in the plant world and are an important way of establishing symbiotic relationships.[3] Ants collect these energy-rich bodies (27.8kJ/g dry weight) and carry them into their nests.[4] Removal of these bodies appears to stimulate the formation of new ones in the same place.[3]The simultaneous presence of pearl bodies, antdomatia andextrafloral nectaries, suggest afacultative plant-antmutualism.[5] Early researchers dubbed these bodies 'perldrüsen' (Meyen 1837), 'pärlharen' (Nils Holmgren 1911) and 'perlules' (Kazimierz Stefan Rouppert 1926). Pearl bodies appear to be the primary, and possibly the only nutrient for ants inhabiting Central Americanmyrmecophytes.[6]
Phytophagous mites such asTetranychus kanzawai have been observed feeding on pearl bodies produced byCayratia japonica of the familyVitaceae, a family in which pearl bodies are common. It also appears possible that the predatory miteEuseius sojaensis uses the pearl bodies as an alternative food source.[7]
Pearl bodies are important in the association between the ant speciesPheidole bicornis and variousPiper species that have spaces between the leaf petiole and stem suitable for use as ant domatia. SomePiper species have stems hollowed out by the ants, while others have naturally hollow stems. These tunnels are 3 – 4 mm in diameter, and, when the ants are in residence, numerous pearl bodies grow from the adaxial surfaces of the petioles, and from the tunnel walls.[8] A study by Deborah K Letourneau in 1983 found that the ants were so sated by the plant's pearl bodies that more than half the insect eggs they encountered while patrolling were dropped to the ground.[9] InMallotus japonicus extrafloral nectaries and pearl bodies function as a biotic defence, while a second line of defence is made uptrichomes and pellucid dots containing toxic secondarymetabolites.[10]
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