The structure and function of the scutellum of the Gramineae

Abstract

NEGBI, M., 1984. The structure and function of the scutellum of the Gramineae. Four kinds of scutella, of which only the first is universally known, can be distinguished in the Gramineae.( I ) The scutellum s e w stricto, the kind most commonly described in textbooks. I n this scutellum the only growth activity during germination is the development of every epithelial cell into a separate elongated papilla. These papillae are involved in secretion of hydrolases, gibberellins and other hormonal factors which in their turn activate the aleurone layer; and in absorption of the mobilized endosperm reserves.(2) The kind characteristic of Auma is found in several genera. In this the scutellar tip elongates during germination, reaches the distal end of the endosperm sac and develops papillae over its whole surface. (3) The kind found in Cizuniu in which the scutellar tip elongates and extends to the far end of the caryopsis during embryo development, but not during germination. In this scutellum only the abaxial surface faces the bulk of the storage endosperm and probably only this surface becomes papillate. Several bamboo genera have the kind of scutellum characterized by Melocannu. This scutellum has evolved as a storage organ and in mature caryopses the endosperm is reduced. This kind is associated with vivipary and with the presence of storage tissue in the pericarp.The vascularization and the structure of the scutellar epithelium, as studied mainly in a limited number of species belonging to the first kind, are related to the functions of the scutellum. The scutellum has a prime role in controlling the mobilization of endosperm reserves.

The scutellar vascular bundle–specific promoter of the wheat HD‐Zip IV transcription factor shows similar spatial and temporal activity in transgenic wheat, barley and rice

“…The pattern of TdGL9H1 expression suggests the involvement of this gene in the formation and ⁄ or maintenance of the main vascular bundle of the scutellum before imbibition and germination. The main vascular bundle of the scutellum has a critical role in controlling the mobilization and transport of endosperm reserves during germination (Price and King, 1973;Sopanen et al, 1977;Moshe Negbi, 1984). Because the activity of the TdGL9H1 promoter was rapidly lost during imbibition, it can be concluded that the gene has no role in vascular bundle regulatory function during germination.…”

The scutellum of Avena: a structure to maximize exploitation of endosperm reserves

“…In reviewing the role of the scutellum, Negbi (1984) concluded that it controls the rate of mobilization of endosperm reserves through three regulatory functions. These are (a) secretion of hormonal messages to the aleurone, (b) secretion of specific hydrolytic enzymes, and (c) absorption and conversion of products of hydrolysis.…”

“…The scutellum possesses a well defined vascular system (Figs 2,3 & 14) which extends from the embryonic axis to within a few cells of the epithelial surface. The considerable literature on scutellar vascularization was reviewed recently by Negbi (1984). Swift & O'Brien (1970, 1971) demonstrated that the composition of the vascular strands in the wheat scutellum changes from an equal proportion of phloem and xylem close to the embryonic node to lOOyo phloem within two or three cells of the epithelium.…”

“…The literature concerning the structure and function of the scutellum was recently reviewed by Negbi (1984). In a classification based on scutellum morphology Avena and a number of other grasses were characterized by a scutellum which elongates during germination and extends into the endosperm in the early stages of seedling establishment.…”

The Evolutionary Conserved Oil Body Associated Protein OBAP1 Participates in the Regulation of Oil Body Size

“…The scutellum is a shield-like structure surrounding the embryo axis that occurs in all grass species, including early diverging taxa, and is generally considered as functionally equivalent to the cotyledon (Negby, 1984;Vernoud et al, 2005). The scutellum plays an important role in the hydrolysis and transport of endosperm-stored substrates during germination, but the scutellum itself also accumulates part of the seed reserves in special lipids (Tzen and Huang, 1992;Subbarao et al, 1998;White and Weber, 2003).…”