Revisiting the histological patterns of storage tissues: beyond the limits of gall-inducing taxa

Abstract

Gall-inducing Aphididae may feed directly on phloem, whereas Eriophyidae and Nematoda feed on cells lining the gall chambers. We assume that a variation in structural complexity will occur within galls induced by each taxon, and that the complexity of the galls could be related to the types of storage tissue they have. Histological, histometric, and histochemical analyses were used to compare six gall systems with different levels of complexity. Such levels are not taxon-related, even though eriophyid galls are usually simpler than nematode and aphid galls. The histological features of galls allowed the classification of storage tissues into three types: typical nutritive tissues (TNT), common storage tissues (CST), and nutritive-like tissues (NLT). The TNT and NLT have cells with dense cytoplasm and a prominent nucleus. The CST cells are vacuolated, and may store starch and other energy-rich molecules, as do the NLT cells. In contrast to NLT or CST, the TNT serves as a direct food source for gall inducers, and it is present in nematode and some eriophyid galls. NLTs may be present in some aphid galls, but are not the direct feeding site. The CST occurs on galls of all three inducing taxa.