Postpollination-prezygotic ovular secretions into the micropylar canal inPseudotsuga menziesii (Pinaceae)

1996 ◽  
Vol 109 (2) ◽  
pp. 147-160 ◽  
Author(s):  
Tokushiro Takaso ◽  
John N. Owens
Keyword(s):  
Micropylar Canal

The Respiratory Mechanisms of Some Insect Eggs

1950 ◽  
Vol s3-91 (16) ◽  
pp. 429-452
Author(s):  
V. B. WIGGLESWORTH ◽  
J.W. L. BEAMENT
Keyword(s):  
Porous Structure ◽  
Outer Layer ◽  
Injection Technique ◽  
Protein Layer ◽  
Insect Eggs ◽  
Quantitative Evidence ◽  
Free Air ◽  
Cobalt Sulphide ◽  
Micropylar Canal

By the use of the cobalt sulphide injection technique the distribution of air in the shell of a number of insect eggs has been studied. Air is usually confined to an inner layer of porous protein, connected with the atmosphere through pores of varying type which are likewise filled with spongy material. In Rhodnius the ‘resistant protein layer’ which lines the shell is the porous structure and the ‘pseudomicropyles’ connect this layer to the exterior. The arrangement in Cimex is similar. In Oncopeltus the spongy walls of the ‘sperm cups’ convey air to a porous inner layer. After laying, the lumen of each cup (the micropylar canal) is occluded with solid cement. In Dixippus the so-called ‘micropyle’ in the ‘scar’ of the egg is the respiratory pore. It is filled with spongy protein containing air and conducts the air to the spongy inner layer of the endochorion. As the egg develops and its contents are reduced in volume, free air collects between the two layers of the endochorion in the region of the pore. In Blattella an elaborate stigmatic apparatus which is moulded in the crista of the oöheca conveys air to a spongy process at the upper pole of the egg and so to a thin porous air-filled layer which lines the chorion. In Bombyx and Ephestia a thin porous inner layer of the chorion containing air communicates with the exterior through scattered pores containing air-filled spongy material. In the eggs of Diptera the chorion consists of tapering columns with spongy walls which unite the cement-covered outer layer to a spongy inner layer containing air. The horns on the Drosophila egg and the dorsal folds on the Calliphora egg provide respiratory outlets for this system. The spaces between the columns contain liquid in Calliphora and Drosophila; in Syrphus these spaces are greatly enlarged and contain air. The spongy layers may become filled with air in eggs which are still bathed in fluid in the oviduct, or in which water is present in adjacent parts of the shell. The mechanism of filling is discussed. In the case of Rhodnius there is quantitative evidence that the system will provide for the respiratory needs of the egg.

Sexual reproduction in western red cedar (Thuja plicata)

1980 ◽  
Vol 58 (12) ◽  
pp. 1376-1393 ◽  
Author(s):  
John N. Owens ◽  
M. Molder
Keyword(s):  
Sexual Reproduction ◽  
Seed Production ◽  
Low Temperatures ◽  
Female Gametophyte ◽  
Seed Set ◽  
Thuja Plicata ◽  
Insect Damage ◽  
Red Cedar ◽  
Pollination Drop ◽  
Micropylar Canal

Pollen cones and seed cones ended dormancy in mid-February, microsporogenesis occurred in late February, and pollination occurred for about 1 week in early March. Pollen was shed at the two-celled stage. Pollination drops were exuded from only a few ovules at one time. Pollen contacting the pollination drop was rapidly taken in. The pollination drop was withdrawn into the micropyle which was later sealed by enlargement of cells lining the micropylar canal. Megasporogenesis occurred in late February but female gametophytes did not mature and fertilization did not occur until late May. An archegonial complex formed containing seven to nine archegonia, of which several usually were fertilized. Proembryo development varied depending upon the size and shape of the archegonia. Usually, a 12-celled, three-tiered proembryo formed by mid-June. Cleavage polyembryony was not observed. Embryos were mature by mid-August and most seed was shed in September and October.The potential seed set was only 16 seeds per cone and filled seed averaged only 2.6 per cone. Most potential seed was lost because of early ovule abortion from unknown causes, insect damage, or low temperatures at or shortly after pollination. Some potential seeds were lost because the ovules were not pollinated or the embryos aborted. These seeds were soft but nearly normal appearing and contained spongy female gametophyte tissue. Methods of maximizing seed production are suggested.

The pollination mechanism and development after bud burst of cones of Larix laricina

1991 ◽  
Vol 69 (6) ◽  
pp. 1179-1187 ◽  
Author(s):  
G. R. Powell ◽  
Kathleen J. Tosh
Keyword(s):  
Key Words ◽  
Seed Size ◽  
Larix Laricina ◽  
Bud Burst ◽  
Scale Growth ◽  
Pollination Mechanism ◽  
Seed Cone ◽  
Cone Development ◽  
Micropylar Canal ◽  
Pollen Cone

Pollen-cone and seed-cone development, from bud burst to maturity, was investigated on Larix laricina (Du Roi) K. Koch in three young plantations. The pollination mechanism was emphasized. Pollen cones grew rapidly to shed pollen, shrivelled, and remained on the trees for a year or more. Pollen was directed to the ovular regions by the bracts of the seed cones. Pollen adhered among papillae on the larger of two integument extensions. Degeneration of the centre of the papillate integument tip caused a collapse that drew pollen in as the papillate rim grew inward. This ingrowth was joined by that of the smaller integument extension, resulting in a sealed tubular structure that enclosed a dry micropylar canal. Pollen was held by the ingrown plug of degenerated tissue as the nucellus tip expanded into the base of the canal. As this occurred, the ovules, with or without pollination, grew to ultimate seed size, and the initially small ovuliferous scales overgrew the bracts. First bract, then ovuliferous-scale growth was associated with a double-sigmoid form of cone elongation. In mature cones the bracts decreased and the ovuliferous scales (except near the tip) increased in size acropetally. Key words: bract, integument, ovuliferous scale, pollen cone, seed cone, tamarack or eastern larch.

Sexual reproduction of Larix occidentalis

1979 ◽  
Vol 57 (23) ◽  
pp. 2673-2690 ◽  
Author(s):  
John N. Owens ◽  
Marje Molder
Keyword(s):  
Female Gametophyte ◽  
Pollen Grains ◽  
Larix Occidentalis ◽  
Embryo Abortion ◽  
Meristematic Tissue ◽  
Micropylar Canal ◽  
Empty Seed ◽  
Mother Cells ◽  
Pollen Cone ◽  
Female Gametophyte Development

Pollen-cone and seed-cone buds broke dormancy about 2 weeks before vegetative buds on the same tree. Pollen mother cells, which had over-wintered at pachytene or the diffuse stage of meiosis, resumed meiosis and tetrads of microspores were formed by mid-March. Wingless five-celled mature pollen developed by mid-to late April when pollination occurred.When development resumed after dormancy a ring of meristematic tissue formed the integument around the nucellus. The integument tip developed a short abaxial tip and a large adaxial lobe on which developed numerous long stigmatic hairs. A slit-like micropyle remained between the two lips. Several pollen grains usually adhered to the stigmatic hairs and then the two lips grew into the micropyle, engulfing the pollen. No pollination drop was observed. Within the micropylar canal, pollen greatly elongated then formed a pollen tube when the elongated pollen contacted the nucellus.Megaspore mother cells underwent meiosis at the time of pollination. Female gametophyte development, which was the same as in most other members of the Pinaceae, was completed in early June and two to five archegonia were formed. Fertilization occurred in early June, 6 to 8 weeks after pollination. A 16-celled proembryo developed. Simple polyembryony was common but cleavage polyembryony was not observed. Embryo development was similar to other members of the Pinaceae. Embryos and seeds were mature by mid-August.Normal appearing but inviable seed is common in L. occidentalis because the ovule is fully enlarged and the seed coat well developed at fertilization. Inviable seed commonly resulted from the absence of pollination, inviable pollen, lack of fertilization, later ovule abortion, or embryo abortion, primarily during early embryonic stages. Flat empty seed also occurred and resulted from abortion of the megaspore mother cell or early female gametophyte.

Comparative study of the eggshell of the fruit flies Dacus oleae and Ceratitis capitata (Diptera: Trypetidae)

1985 ◽  
Vol 63 (9) ◽  
pp. 2194-2206 ◽  
Author(s):  
Lukas H. Margaritis
Keyword(s):  
Biochemical Analysis ◽  
Ceratitis Capitata ◽  
Light And Electron Microscopy ◽  
Fruit Fly ◽  
Fruit Flies ◽  
Olive Fruit Fly ◽  
Dacus Oleae ◽  
Structural Functions ◽  
Micropylar Canal ◽  
Eggshell Proteins

The eggshell of two fruit flies of economic importance has been studied by means of light and electron microscopy. The eggshell of the olive fruit fly, Dacus oleae, contains compact endochorion, whereas that of the Mediterranean fruit fly, Ceratitis capitata, exhibits a holey endochorionic layer. The eggshells of both species have an innermost chorionic layer which appears to be crystalline in substructure. The anterior pole in each case contains the micropylar canal but in addition it bears an elaborate "cup" in Dacus oleae. Both species exhibit peroxidase activity in most eggshell layers and, as in the case of Drosophila melanogaster, it is thought that the enzyme causes covalent cross-linking of the eggshell proteins producing a resilin-type configuration with rubberlike properties. The above features are related to specific structural functions of the eggshell during fertilization, oviposition, and respiration of the embryo. Biochemical analysis has revealed that the two species have very few eggshell proteins that are similar in molecular weight.

A cell biological study of the micropylar apparatus in dipterans of economic importance

1990 ◽  
Vol 48 (3) ◽  
pp. 484-485
Author(s):  
Flora E. Zarani ◽  
Lukas H. Margaritis
Keyword(s):  
Ceratitis Capitata ◽  
Anterior Part ◽  
Economic Importance ◽  
Follicle Cells ◽  
Biological Study ◽  
Vitelline Membrane ◽  
Micropylar Canal ◽  
A Cell ◽  
Specialized Region ◽  
Rhagoletis Cerasi

The micropylar apparatus is a specialized region of the eggshell, serving as a passage (micropylar canal) to the spermatozoon. The entire eggshell is secreted by the follicle cells during oogenesis, in successive layers, in the following order: vitelline membrane, wax layer, innermost chorionic layer, endochorion, exochorion. This study is an E.M. investigation of the structure and morphogenesis of the micropylar apparatus at the follicles of Dipterans of economic importance, such as Ceratitis capitata, Dacus oleae and Rhagoletis cerasi. These insects affect the fruits of orange, olive and cherry trees respectively.The micropylar apparatus of the Dipterans C. capitata, D. oleae and R. cerasi. forms a protrusion at the anterior part of the egg. This apparatus consists of the vitelline membrane (Vm), which is surrounded by the wax layer (wl); the innermost chorionic layer (icl); the endochorion (En); and the exochorionic “tuft”. The endochorion has many cavities which probably take part in the air storage, in order to facilitate the embryo’s respiratory needs (Figs. 1,3,5). The micropylar canal is covered by the characteristic tuft, resulting in the vitelline membrane, where it becomes thinner and forms the pocket.

Prefertilization events in ovules of Pseudotsuga: ovular secretion and its influence on pollen tubes

1996 ◽  
Vol 74 (8) ◽  
pp. 1214-1219 ◽  
Author(s):  
T. Takaso ◽  
P. von Aderkas ◽  
J. N. Owens
Keyword(s):  
Relative Humidity ◽  
Pollen Tube ◽  
Sexual Reproduction ◽  
Morphological Study ◽  
Pollen Tubes ◽  
High Relative Humidity ◽  
Starch Grains ◽  
Body Cell ◽  
Egg Formation ◽  
Micropylar Canal

A natural ovular secretion from the megagametophyte, essential to sexual reproduction, was examined in Pseudotsuga. This secretion began soon after egg formation or about 1 week before fertilization. Secreted fluid filled the micropylar canal. Morphological study showed that the fluid affected (i) dissolution of intine materials; (ii) pollen distortion that may relate to prezygotic selection; and, (iii) induction of pollen tubes. The origin of the secreted fluid is interpreted from an experiment using homogenates. Elongated pollen supplied with a homogenate of the megagametophyte shows immediate movement of starch grains and body cell. Some pollen formed pollen tubes. Homogenates of the nucellus or the integument elicited little or no response. If ovules are dissected before the natural secretion and kept in high relative humidity, the micropylar canal becomes filled with fluid. This fluid is an artifact resulting from dissection, but is also capable of inducing pollen tubes. Keywords: megagametophyte, ovule, pollen tube, Pseudotsuga, secretion.

The pollination mechanism and the optimal time of pollination in Douglas-fir (Pseudotsugamenziesii)

1981 ◽  
Vol 11 (1) ◽  
pp. 36-50 ◽  
Author(s):  
John N. Owens ◽  
Sheila J. Simpson ◽  
Marje Molder
Keyword(s):  
Electron Microscopy ◽  
Seed Set ◽  
Pollen Grains ◽  
Douglas Fir ◽  
Optimal Time ◽  
Pollination Mechanism ◽  
Seed Cone ◽  
Poor Seed ◽  
Micropylar Canal ◽  
Scanning Electron

The development of the pollination mechanism and the engulfment of pollen by the stigmatic tip is described for Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) based on scanning electron microscopy. This information is used to determine and explain the optimal time of pollination and amount of pollen needed for maximum seed set. After dormancy the integument tip of the ovule developed into an unequally two-lobed stigmatic tip covered with long unicellular hairs. Most ovules had fully developed stigmatic tips when the seed cone emerged from the bud scales in early April. The conelets remained open and the stigmatic tip was most receptive for at least 4 days. Pollen freely sifted down between the bracts and ovuliferous scales and adhered to the stigmatic hairs. Six days after the conelets became receptive, stigmatic hairs around the micropyle began to collapse and were ungulfed with the entangled pollen into the micropyle. Also, ovuliferous scales began to thicken, restricting movement of pollen to the stigmatic tips. By 8–10 days after conelets became receptive, the stigmatic tips were completely engulfed, the ovuliferous scales had thickened enough to close the conelet, and the conelet had begun to bend down.Maximum seed set occurred when (1) cones were pollinated within 4 days after seed-cone buds had emerged half of the way out of their bud scales; (2) a minimum of 0.2 g of pollen was used per pollination bag; (3) a minimum of 11 pollen grains adhered to each stigmatic tip; and (4) at least 3 pollen grains were taken into each micropylar canal. The engulfing process occurred at the same rate and in the same manner regardless of whether living or heat-killed pollen was present or absent on the stigmatic surface. Poor seed set as it related to the pollination mechanism is discussed.

Sexual reproduction of mountain hemlock (Tsuga mertensiana)

1975 ◽  
Vol 53 (17) ◽  
pp. 1811-1826 ◽  
Author(s):  
John N. Owens ◽  
Marje Molder
Keyword(s):  
Cell Walls ◽  
Pollen Tubes ◽  
Linear Tetrad ◽  
Form Complex ◽  
Male Gametes ◽  
Canal Cell ◽  
Micropylar Canal ◽  
Tsuga Mertensiana ◽  
Mother Cells ◽  
Ventral Canal

Meiosis of pollen mother cells begins in October of the year in which cones are initiated. They reach pachytene then become dormant until the next March. Meiosis is complete and the winged pollen mature by mid-June. Meiosis of the megaspore mother cell occurs in May, forming a linear tetrad of megaspores. The female gametophyte undergoes free nuclear division at pollination in mid-June. No pollination drop is present; rather, the pollen adheres to the sticky, splayed edge of the micropyle, where it germinates and pollen tubes grow toward the nucellus. The nucellus elongates into the micropylar canal, forming a nucellar beak, which makes contact with the pollen tubes. Several pollen tubes penetrate the nucellus.At the time of fertilization early in August, each ovule contains two to four aichegonia each having two to four neck cells in one tier. Pollen tubes penetrate the neck cells and two male gametes are formed. The ventral canal cell breaks down and fusion occurs in the center of the archegonium. Four free nuclei form and migrate to the base of the archegonium. cell walls form, and a 16-celled proembryo develops. Both simple and cleavage polyembryony occur. Rosette cells divide but do not form complex embryos. The embryo and seed are mature in October and the cones dry and open during October and November. Mature cones averaged 70 seeds, of which 46% were filled.Reproduction in mountain hemlock (Tsuga mertensiana (Bong.) Carr.) is similar to that in other species of Tsuga except for the presence of winged pollen. Any attempt to place the species in the genus Picea or place it as a hybrid midway between Picea and Tsuga is unfounded based on all of the more-conservative reproductive and embryological characteristics.

Factors inducing closure of the micropylar canal in the chum salmon egg

1993 ◽  
Vol 42 (3) ◽  
pp. 385-394 ◽  
Author(s):  
W. Kobayashi ◽  
T. S. Yamamoto
Keyword(s):  
Chum Salmon ◽  
Micropylar Canal
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