The gametophytic genomic component and a callose
wall are missing in the orbicule model and yet a patterned accumulation of sporopollenin with similar ornamentation to the pollen wall (Hesse, 1986; Huysmans et al.
The hypothesized function of ligules can be grouped into three categories: organ of absorption (Mc Nab, 1887; Kohlenbach and Geier, 1970); secretion of water or mucilage (Hofineister, 1851; Harvey Gibson, 1896; Maslen, 1898; Foster and Gifford, 1959; Bierhorst, 1971; Bilderback and Slone, 1987; and Bilderback, 1987); production of callose
(Jagels and Garner, 1979) or complex carbohydrate (Sigee, 1976).
content was determined by using a JASCO Spectrofluorometer FP-777 (Japan Spectroscopic Co, Ltd, Tokyo) with excitation at 350 nm and emission at 500 nm.
Microsporogenesis can be described as simultaneous if cytokinesis and callose
deposition both occur after meiotic divisions are complete.
The sporocyte wall, usually consisting of callose
or mucopolysaccharides, isolates cells programmed to enter the meiotic pathway from the influence of surrounding vegetative cells.
is a beta--1, 3-glucan polymer of glucose, a major component of inducible plant cell wall apposition and a barrier against fungal infection.
deposits in pollen tubes: an apparent necessity for extended siphonogamy, because it compartmentalizes the male gamete apparatus.
In early stage of meiosis, Microsporocytes separate with callose
walls; tapetal cells more or less enlarge (Fig.
In Heliconia, a single stamen develops as an infertile, often callose
, staminode (Kirchoff et al.
is rapidly synthesized in the plasma membrane as an early
The HR involves a multitude of biochemical events in the plant, including: synthesis of ethylene and phytoalexins; reinforcement of the cell wail with callose
, lignin, and related compounds; accumulation of glycoproteins rich in hydroxyproline at the limit of the cell wall; and synthesis of pathogenesis-related proteins (PRP), these including glucanases, quitanases, proxidases, and protein inhibitors (Dixon & Lamb, 1990).
As the pollen mother cells separate and develop callose
walls, the tapetal cells enlarge, but do not penetrate the spaces between the pollen mother cells [ILLUSTRATION FOR FIGURES 51, 65 OMITTED].