Nondispersive Protein Bodies in Sieve Elements: A Survey and Review of their Origin, Distribution and Taxonomic Significance

Abstract

Nondispersive protein bodies present in the sieve elements in addition to dispersive P-protein are characteristic features of many woody dicotyledons; their origin may be nuclear or cytoplasmic. While nuclear nondispersive protein bodies are found in only two families, the Boraginaceae and Myristicaceae, bodies of cytoplasmic origin are present in 39 of the more than 350 families screened. These results were obtained from 228 dicotyledons studied with the electron microscope and data of additional species from the literature. The terminology, origin, form and distribution of nondispersive protein bodies are discussed. Their ultrastructural composition is described as being predominantly spindle-shaped, compound- spherical, rod-shaped and rosette-like. Based on the data accumulated from over 450 species (of about 3000 screened) it is evident that their taxonomic range is confined to a few dicotyledon superorders. Compound-spherical nondispersive protein bodies are characteristic of most of the Malvanae/Violanae; spindle-shaped forms are restricted to the Fabaceae (Rutanae). Rosanae-Proteanae-Myrtanae and the Magnolianae are the only other superorders that contain nondispersive protein bodies in several of their families. Evolutionary trends and possible taxonomic consequences implied in this distribution are discussed.