INTRODUCTIONMaize (Zea mays L.) is the world's second most important food crop. Its overall yield is determined by several parameters: number of plants per unit of land, number of ears per plant, number of kernels per ear, and kernel size. The last parameter is frequently correlated with the length of the grain-filling period [ 1-41, During grain filling, which ends with the appearance of a black layer of cells at the base of the pedicel [3], the morphogenic event that plays the most important role in determining maize yield is the development and maturation of the endosperm. The endosperm is a triploid tissue specialized mainly in the storage of starch and proteins; it represents more than 80% of the final seed weight. The length of the period necessary for grain filling is under strict genetic control [ l , 5-71. It contains three distinct phases 181: 1) a lag period of grain dry-matter accumulation that starts at silk emergence and extends for 15 to 18 days; 2) a period of linear grain dry-weight accumulation during which more than 90% of grain dry-matter is accumulated; and 3) a period in which the rate of dry weight accumulation of the grain declines, terminating with black cell layer formation.
GENE SYMBOLSA , anthocyanin (colored aleurone); Ac, activator; ae, amylose extender; al, albescent: hr. brittle: Bz, bronze; Bn, brown aleurone; C , colored aleurone; cl. chlorophyll; cp, collapsed; de, defective endosperm; De*-B30, defective endosperm (opaque); dek, defective kernel; Ds, dissociation; du, dull endosperm; et, etched; jl2, floury endosperm; ly, lycopenic; Iw, lemon white; Mc, mucronate (opaque); mn, miniature; o, opaque endosperm; pro, proline requiring; p s , pink scutellum; R, colored aleurone; re, reduced endosperm; sh, shrunken endosperm; su. sugary; st, sticky chromosome; y , viviparous; w3, white (endosperm and seedling); Wc, white cap; wx, waxy endosperm; y . yellow endosperm; 7 , zeta-carotenic.Received for publication September 20, 1983; accepted March 1, 1984. Address reprint requests to C. Soave, Istituto Biosintesi Vegetali C.N.R., Via Bassini, 15 Milano, Italy. 0 1984 Alan R. Liss, Inc.
Soave and SalaminiIn maize [9, 101, as in other cereals [ll-131, endosperm cell number influences the rate of grain filling, grain size, and final yield more than does cell size. Cell number of the endosperm is determined in the lag period when mitotic divisions can be easily observed in the tissue [14,15]. At present, there is a lack of information concerning this developmental phase. Several studies have been directed toward the filling phase of endosperm development [reviewed in [16][17][18][19]. They considered in particular the mechanisms that control starch and storage protein deposition. Besides clarifying important aspects of endosperm physiology, the genetic and nutritional discoveries made in this area are the basis for the development of new strains of cereals with superior nutritional qualities [summarized in 201. It is important to understand all aspects of endosperm development, since ...
