The pollen wall of Canna and its similarity to the germinal apertures of other pollen.
TL;DR: It is suggested that the entire pollen wall of C. generalis is similar to the thick intine and thin exine typical for germinal apertures in many pollen grain types.
Abstract: A B S T R A C T The pollen wall of Canna generalis Bailey is exceptionally thick, but only a minor part of it contains detectable amounts of sporopollenin. The sporopollenin is in isolated spinules at the exine surface and in the intine near the plasma membrane. There is no sporopollenin in the > 10 ,u thick channeled region between spinules and intine. We suggest that the entire pollen wall of C. generalis is similar to the thick intine and thin exine typical for germinal apertures in many pollen grain types. Considered functionally, the Canna pollen wall may offer an infinite number of sites for pollen tube initiation and would differ significantly from grains that are inaperturate in the sense of an exine lacking definite germinal apertures. THE CANNACEAE are represented by a single genus, Canna, and approximately 50 species. The extensive use of Canna as an ornamental has resulted in numerous hybrids. In a pollen morphological investigation of 48 horticultural varieties of C. indica significant differences were noted in wall ornamentation, sterility, and size (Nair, 1960). The exine stratification patterns, however, have been difficult to interpret as Erdtman (1952) suggested. Sporopollenin as part of an exine is recognized only in spinules at the pollen wall surface but staining of Canna microspores with osmium indicated that there were inclusions within the intine and in the tryphine on the wall surface which looked like sporopollenin. To substantiate the presence of sporopollenin in the above nonexinous locations we followed the disintegration of Canna pollen caused by the acetolysis method of Erdtman (1960). It became evident that the entire wall was similar to the greatly thickened intine and thin exine common to the germinal apertures of many pollen grains. We have drawn upon original electron micrographs of Centrolepis aristata (R. Br.) Roem. and Schultz. and Macrozamia reidlei (Gaud.) C. A. Gardn. to amplify the latter aspect of our results.
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TL;DR: Two features make the angiosperm male gametophyte almost unique among higher organisms, namely the versatility expressed by a single haploid cell, and the degree of coadaptation it shows with its diploid host.
Abstract: Publisher Summary Pollen germination and pollen-tube growth events when viewed either in culture or in the style are considered as biochemically, physiologically, and structurally complex. The various processes involved are each independent in some measure, but still all are interactive—namely, the successful attainment of the delivery of two male gametes into the embryo sac, requires a high degree of coordination within the male gametophyte and at the same time a remarkable sensitivity to a considerable range of influences both in the physical environment and in the pistil. Much of the activity of the vegetative cell has the air of being preprogrammed; and this must be so in those species where there is little or no gene transcription in the vegetative nucleus. The capacity to function successfully in a complex and varying environment betokens a high degree of self-regulation. Some of the feedback mechanisms likely to contribute to stability are reviewed. They are analogous with the homeorhetic systems postulated in other instances of biological development. However, two features make the angiosperm male gametophyte almost unique among higher organisms, namely the versatility expressed by a single haploid cell, and the degree of coadaptation it shows with its diploid host.
418 citations
TL;DR: Pollens of certain Cruciferae produce tubes capable of penetrating the Crocus stigma cuticle, suggesting that notwithstanding the taxonomie remoteness of Crucifierae and Iridaceae the enzyme activation systems are quite similar.
233 citations
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01 Jan 1984
TL;DR: The pollen grain is the carrier of the male gametes or their progenitor cell, in higher plants, and contains all the genetic information required to specify an entire haploid plant organism.
Abstract: The pollen grain is the carrier of the male gametes or their progenitor cell, in higher plants In a single unit, each grain contains all the genetic information required to specify an entire haploid plant organism (for example, pollen embryoids in tissue culture), or to unite with the female gamete at fertilization and form a diploid zygote and, hence, a new sporophyte The male gametes, the sperm cells (or their progenitor, the generative cell) are housed entirely within the cytoplasm of the vegetative cell This is dehydrated like a seed at maturity, and is filled with storage reserves The vegetative cell is surrounded by a complex, intricately patterned outer wall, and its nucleus controls at least the initial growth and metabolism of the pollen tube following germination
186 citations
175 citations
TL;DR: The evolutionary trends of pollen apertures and wall structure in the monocots parallel those proposed by Walker for the dicots, however, the importance of these trends differ for monocot, suggesting that the selective pressures affecting pollen wall and aperture evolution in dicotylédones have been similar, but with different emphasis.
Abstract: Data on pollen aperture and wall ultrastructure are reviewed for the monocots. New ultrastructural data on 30 taxa representing 18 monocot families are also presented. The evolutionary trends of apertures and pollen wall structure are discussed and it is proposed that the evolutionary trends of pollen apertures and wall structure in the monocots parallel those proposed by Walker for the dicots. However, the importance of these trends differ for monocots, suggesting that the selective pressures affecting pollen wall and aperture evolution in dicots and monocots have been similar, but with different emphasis.
155 citations
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TL;DR: The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present, and is less likely to contaminate sections.
Abstract: Aqueous solutions of lead salts (1, 2) and saturated solutions of lead hydroxide (1) have been used as stains to enhance the electron-scattering properties of components of biological materials examined in the electron microscope. Saturated solutions of lead hydroxide (1), while staining more intensely than either lead acetate or monobasic lead acetate (l , 2), form insoluble lead carbonate upon exposure to air. The avoidance of such precipitates which contaminate surfaces of sections during staining has been the stimulus for the development of elaborate procedures for exclusion of air or carbon dioxide (3, 4). Several modifications of Watson's lead hydroxide stain (1) have recently appeared (5-7). All utilize relatively high pH (approximately 12) and one contains small amounts of tartrate (6), a relatively weak complexing agent (8), in addition to lead. These modified lead stains are less liable to contaminate the surface of the section with precipitated stain products. The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present. Lead citrate, soluble in high concentrations in basic solutions, is a chelate compound with an apparent association constant (log Ka) between ligand and lead ion of 6.5 (9). Tissue binding sites, presumably organophosphates, and other anionic species present in biological components following fixation, dehydration, and plastic embedding apparently have a greater affinity for this cation than lead citrate inasmuch as cellular and extracellular structures in the section sequester lead from the staining solution. Alkaline lead citrate solutions are less likely to contaminate sections, as no precipitates form when droplets of fresh staining solution are exposed to air for periods of up to 30 minutes. The resultant staining of the sections is of high intensity in sections of Aralditeor Epon-embedded material. Cytoplasmic membranes, ribosomes, glycogen, and nuclear material are stained (Figs. 1 to 3). STAIN SOLUTION: Lead citrate is prepared by
24,137 citations
Journal Article•
1,900 citations
Journal Article•
1,782 citations
TL;DR: In this article, Pollen Morphology and Plant Taxonomy is discussed. But the focus is on plant taxonomy, and not on pollen morphology and taxonomy of plants.
Abstract: (1952). Pollen Morphology and Plant Taxonomy. Geologiska Foreningen i Stockholm Forhandlingar: Vol. 74, No. 4, pp. 526-527.
1,557 citations
TL;DR: It is thought that in these highly alkaline staining solutions lead is present as an hydroxide complex anion (plumbite ion) and that this anion is responsible for the staining, and the methods of preparation are based on this hypothesis.
Abstract: The lead hydroxide stain of Watson (1958) used for increasing contrast in thin sections for electron microscopy has found acceptance in many laboratories. However, this stain has an unfortunate tendency to form precipitates (probably of lead carbonate (5)) on exposure to the air, thus contaminating the sections and irritating the observer. This drawback has led to the development of several modifications (2, 3) of the original method of staining and the use of ingenious devices (4, 5) for preventing exposure to air and consequent precipitate formation. We offer the following alternative methods which, we believe, are simpler to perform than those hitherto described. They have the additional advantages mentioned below. The methods are based on the observation that highly alkaline solutions of lead salts (pH > 11.5) yield relatively stable solutions which stain rapidly and intensely, thus obviating the hazard of precipitation to a marked degree. The methods have these additional advantages: the staining solutions are easily and rapidly prepared, are simply stored, and are stable for long periods of time. Furthermore, they can be efficiently used, many grids being treated simultaneously, without excessive precautions being taken against lead carbonate precipitation. Finally, \"difficult\" material, embedded in media which characteristically yield rather low contrast, such as epoxide resins, can be rapidly and easily stained. \"C lean\" preparations, of high contrast, are routinely obtained. As will be discussed later, it is thought that in these highly alkaline staining solutions lead is present as an hydroxide complex anion (plumbite ion) and that this anion is responsible for the staining. The methods of preparation are based on this hypothesis. Two methods for preparing the staining solutions have been found useful:
1,298 citations