Histochemistry and fine structure of developing wheat aleurone cells

Abstract

Developing aleurone cells can first be distinguished 10 days after anthesis beneath the degenerating nucellus as somewhat cuboidal cells with extremely thin walls and large nuclei. Ribosomes are very abundant but little endoplasmic reticulum (ER) is apparent. By 14 days the cell walls are intensely autofluorescent, possibly due to the presence of a ferulic acid-carbohydrate complex. At this stage the cytoplasm is characterized by the presence of large vacuoles, many of which contain small, electron-dense inclusions, presumably the beginnings of the phytin globoids (Type I inclusions) of mature aleurone grains. The paired appearance of many of the cells suggests that they are dividing periclinally, the innermost cells destined to become part of the starchy endosperm. By 4 weeks the cell walls have greatly thickened, ER and mitochondria have proliferated, and the vacuoles, which subsequently give rise to mature aleurone grains, contain a second type of inclusion (Type II inclusion) embedded in a protein matrix. Although the walls remain uniformly autofluorescent, an intensely stained inner wall can be distinguished readily from the outer wall. By 5 weeks the aleurone grains are almost completely surrounded by lipid droplets and contain numerous Type I inclusions. The cells change little in appearance from 6 weeks to maturity. At the latter stage the inner and outer walls are quite distinct and the cytoplasm is densely packed with aleurone grains which are completely surrounded by lipid droplets and interspersed with occasional plastids and numerous mitochondria with rather indistinct cristae.

Surface Position, Not Signaling from Surrounding Maternal Tissues, Specifies Aleurone Epidermal Cell Fate in Maize

“…First, our data confirm and expand on the importance of surface position for aleurone cell fate specification. In accordance with observations from wheat and maize (Morrison et al, 1975;Becraft and Asuncion-Crabb, 2000), inner daughter cells of periclinally dividing aleurone cells assumed starchy endosperm cell fate as demonstrated by the rapid loss of Ltp2:ZsYellow fluorescence. Also, we demonstrate that the endosperm has full flexibility to respond to positional information by converting between starchy endosperm and aleurone cell fate in response to position throughout the endosperm.…”

“…Research has shown that positional signaling plays a pivotal role in determining aleurone cell fate specification. Observations from wheat (Triticum aestivum), and later from maize, have provided indications that positional signaling is involved as periclinal (inner) daughters of dividing aleurone cells converted to become starchy endosperm cells upon internalization (Morrison et al, 1975;Becraft and Asuncion-Crabb, 2000). Defective kernel 1 (Dek1) revertant sector analysis reinforced this conclusion, supporting the notion that aleurone cell fate specification is independent of cell lineage and dependent on positional signaling (Becraft and Asuncion-Crabb, 2000).…”

Nuclear Endosperm Development in Cereals and Arabidopsis thaliana

“…Aleurone cells become morphologically distinct in barley endosperm at 8 DAP (Bosnes et al, 1992), comparable to the other cereals (Morrison et al, 1975;Brown et al, 1999). GUS expression driven by the barley Ltp2 promoter in transgenic rice grains is detectable at 9 DAP, closely matching the morphological differentiation of aleurone cells (Kalla et al, 1994).…”

X-ray Analysis Studies of Elements Stored in Protein Body Globoid Crystals of Triticum Grains

“…Past studies have concentrated upon endosperm, including aleurone (2,4,10,25,26,36,38), and scutellum (28,32,41,42,43), but studies of other embryo regions have also been made (32). From the studies listed above, it is clear that distinct globoid crystals are commonly found in protein bodies in aleurone cells and embryo cells but are lacking in starchy endosperm cell protein bodies.…”