The pollination mechanism in yellow cypress (Chamaecyparisnootkatensis)

1980 ◽  
Vol 10 (4) ◽  
pp. 564-572 ◽  
Author(s):  
John N. Owens ◽  
Sheila J. Simpson ◽  
Marje Molder
Keyword(s):  
Lipid Droplets ◽  
Pollen Grains ◽  
Water Droplets ◽  
Pollination Mechanism ◽  
Seed Cone ◽  
Pollination Drop ◽  
Micropylar Canal ◽  
The One ◽  
Cuticular Surface

Mature, dry, one-celled pollen was formed before pollen cones became dormant in the fall. Pollen averaged 27 μm in diameter, was irregular in shape, nonsaccate, and the surface was reticulate to tegillate-baculate and irregularly covered with orbicules. The pollen contained several large lipid droplets and no starch. No changes occurred in pollen during dormancy and pollen was shed at the one- or two-celled stage during the last half of March.All ovules were initiated and became flask shaped before seed-cone dormancy. No changes occurred in ovules during dormancy. Seed cones ended dormancy in early March, enlarged and opened, exposing the ovules. A pollination drop was produced by a breakdown of cells at the tip of the nucellus. A large pollination drop was exuded from each ovule in a cone but exudation did not occur at the same time in all ovules. Each ovule exuded and withdrew a pollination drop two to four times before the pollination drop was permanently withdrawn. Each ovule was receptive for a few days and each cone was receptive for about 1 week. The pollination drops were withdrawn in the presence or absence of pollen but were withdrawn more rapidly after pollen entered the pollination drop. The cuticular surface of the bract-scales prevented wetting of the surface and caused the beading of water droplets, which in turn could carry pollen to the micropyle. Pollen grains entering a pollination drop were withdrawn inside the drop into the micropyle. Cells lining the micropylar canal enlarged and sealed the canal while bract-scales enlarged and buried the ovules within the cone.

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.

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.

Postdormancy seed-cone development and the pollination mechanism in western hemlock (Tsugaheterophylla)

1989 ◽  
Vol 19 (1) ◽  
pp. 44-53 ◽  
Author(s):  
Anna M. Colangeli ◽  
John N. Owens
Keyword(s):  
Pollen Grains ◽  
Pollen Tubes ◽  
Epicuticular Wax ◽  
Western Hemlock ◽  
Bud Burst ◽  
Pollination Mechanism ◽  
Seed Cone ◽  
Cone Development ◽  
And Function

The development and function of the pollination mechanism is described for hemlock (Tsugaheterophylla (Raf.) Sarg.). Controlled pollinations at various stages following bud burst were used to define the period of maximum receptivity. Western hemlock has a pollination mechanism unlike that observed in other native conifers. The pollen grains were not taken into the micropyles; instead, the roughly sculptured pollen grains adhered to the long epicuticular wax covering the bracts. Seed cones became receptive to pollen soon after the bracts emerged from the bud scales and remained receptive until shortly before cone closure. Several days after the cones fully emerged beyond the bud scales, the ovuliferous scales elongated over the bracts, trapping the pollen between the bracts and scales. Several weeks after pollination, pollen germinated on the bracts and formed long pollen tubes which grew towards and into the micropyles.

The pollination mechanism of Sitka spruce (Picea sitchensis)

1984 ◽  
Vol 62 (6) ◽  
pp. 1136-1148 ◽  
Author(s):  
John N. Owens ◽  
Margaret D. Blake
Keyword(s):  
Sitka Spruce ◽  
Picea Sitchensis ◽  
Optimal Time ◽  
Secretory Cells ◽  
Drop Formation ◽  
Winter Dormancy ◽  
Pollination Mechanism ◽  
Seed Cone ◽  
Pollination Drop ◽  
And Function

The development and function of the pollination mechanism and the optimal time for pollination are described for Sitka spruce (Picea sitchensis (Bong.) Carr.). After winter dormancy, the rudimentary integument overgrew the nucellus and formed two long micropylar arms. Soon after seed-cone buds burst, the epidermal cells on the micropylar arms secreted mucilage droplets to which pollen adhered. The ultrastructure of mucilage droplet secretion is described. After 6–8 days a pollination drop formed from the nucellus. This filled the space between the micropylar arms and picked up any pollen which adhered to the arms or landed on the pollination drop. The pollination drop was then withdrawn carrying pollen into the micropyle. The secretory cells on the micropylar arms then autolyzed and a large mucilage plug sealed the micropyle and filled the space between the withered micropylar arms. Conelets closed and became pendant. Pollen germinated and pollen tubes formed about 2 weeks after pollination ended. Conelets enclosed in pollination bags were open and receptive for about 10 days, but the optimal time for pollination was 6 to 8 days after cone buds burst. This coincided with the time of pollination-drop formation.

Pollen scavenging and rain involvement in the pollination mechanism of interior spruce

1996 ◽  
Vol 74 (1) ◽  
pp. 115-124 ◽  
Author(s):  
C. John Runions ◽  
John N. Owens
Keyword(s):  
Picea Glauca ◽  
Selective Pressure ◽  
Seed Orchard ◽  
Picea Engelmannii ◽  
Pollination Efficiency ◽  
Pollination Mechanism ◽  
Pollination Mechanisms ◽  
Seed Cone ◽  
Interior Spruce ◽  
Pollination Drop

Pollination drops are secreted from the ovules of interior spruce (Picea glauca or Picea engelmannii and their hybrid) as seed cones begin to close at the end of the pollination period. Secreted pollination drops persist within spaces surrounding the micropylar opening in closed seed cones. Saccate pollen floats into the micropyle within the pollination drop. Pollination drops become voluminous enough, within the enclosed spaces, to scavenge pollen adhering to the micropylar arms and other surfaces in proximity with the micropyle. Scavenging of pollen from cone surfaces adjacent to the integuments is sometimes facilitated by rainwater that can float pollen into the opening of the micropyle before cone closure and pollination drop secretion. In practice, periodic, light misting of seed orchard trees during seed cone receptivity might increase pollination efficiency by mimicking rainwater involvement in the pollination mechanism. Rainwater involvement in pollination of some modern conifers may reflect a similar situation in the pollination mechanisms of ancestral conifers. Environments with limited rainfall combined with the requirement for moisture in the pollination mechanism may have provided the selective pressure for evolution of the pollination drop. Keywords: pollination drop, Picea, conifer, sacci.

scholarly journals ROS in tobacco stigma exudate affect pollen proteome and provoke membrane hyperpolarization

2020 ◽  
Author(s):  
Breygina Maria ◽  
Klimenko Ekaterina ◽  
Shilov Eugeny ◽  
Mamaeva Anna ◽  
Zgoda Viktor ◽  
...  
Keyword(s):  
Cell Metabolism ◽  
Pollen Grains ◽  
Plant Reproduction ◽  
List Type ◽  
Membrane Hyperpolarization ◽  
Inhibitory Analysis ◽  
The One ◽  
Cellular Components ◽  
Stigma Exudate

1.AbstractROS are known to be accumulated in stigmas of different species and can possibly perform different functions in plant reproduction. Here we confirm the assumption that they affect pollen by altering ion transport through the plasma membrane; as a more deferred effect, pollen proteome is modified. We detected ROS in stigma exudate, found hyperpolarization in exudate-treated growing pollen tubes and used flow cytometry of pollen protoplasts to compare the effects of fresh exudate and exogenous H2O2 on pollen tube plasmalemma. Exudate causes plasmalemma hyperpolarization similar to the one provoked by H2O2, which is abolished by catalase treatment and ROS quencher MnTMPP. Inhibitory analysis indicates the participation of Ca2+- and K+-conducting channels in the observed hyperpolarization, linking obtained data with previous patch-clamp studies in vitro. For a deeper understanding of pollen response to ROS we analyzed proteome alterations in H2O2-treated pollen grains. We found 50 unique proteins and 20 differently accumulated proteins that are mainly involved in cell metabolism, energetics, protein synthesis and folding. Thus, pollen is getting ready for effective resource usage, construction of cellular components and rapid growth.HighlightsThe active substance in stigma exudate is H2O2H2O2 causes hyperpolarization mediated by the activation of cation channels.H2O2 affects pollen proteome; we found 50 unique proteins.

scholarly journals Development of Embryo Suspensors for Five Genera of Crassulaceae with Special Emphasis on Plasmodesmata Distribution and Ultrastructure

Plants ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 320 ◽  
Author(s):  
Małgorzata Kozieradzka-Kiszkurno ◽  
Daria Majcher ◽  
Emilia Brzezicka ◽  
Joanna Rojek ◽  
Justyna Wróbel-Marek ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Basal Cell ◽  
Lipid Droplets ◽  
Cell Structure ◽  
Cell Transfer ◽  
Electron Dense Material ◽  
Full Development ◽  
The One ◽  
Embryonic Structure ◽  
Suspensor Cells

The suspensor in the majority of angiosperms is an evolutionally conserved embryonic structure functioning as a conduit that connects ovule tissues with the embryo proper for nutrients and growth factors flux. This is the first study serving the purpose of investigating the correlation between suspensor types and plasmodesmata (PD), by the ultrastructure of this organ in respect of its full development. The special attention is paid to PD in representatives of Crassulaceae genera: Sedum, Aeonium, Monanthes, Aichryson and Echeveria. The contribution of the suspensor in transporting nutrients to the embryo was confirmed by the basal cell structure of the suspensor which produced, on the micropylar side of all genera investigated, a branched haustorium protruding into the surrounding ovular tissue and with wall ingrowths typically associated with cell transfer. The cytoplasm of the basal cell was rich in endoplasmic reticulum, mitochondria, dictyosomes, specialized plastids, microtubules, microbodies and lipid droplets. The basal cell sustained a symplasmic connection with endosperm and neighboring suspensor cells. Our results indicated the dependence of PD ultrastructure on the type of suspensor development: (i) simple PD are assigned to an uniseriate filamentous suspensor and (ii) PD with an electron-dense material are formed in a multiseriate suspensor. The occurrence of only one or both types of PD seems to be specific for the species but not for the genus. Indeed, in the two tested species of Sedum (with the distinct uniseriate/multiseriate suspensors), a diversity in the structure of PD depends on the developmental pattern of the suspensor. In all other genera (with the multiseriate type of development of the suspensor), the one type of electron-dense PD was observed.

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.

Further observations on the pollination mechanism and seed production of Douglas-fir

1982 ◽  
Vol 12 (2) ◽  
pp. 431-434 ◽  
Author(s):  
John N. Owens ◽  
Sheila J. Simpson
Keyword(s):  
Seed Production ◽  
Pollen Grains ◽  
Germination Percentage ◽  
Douglas Fir ◽  
Pollination Mechanism ◽  
Supplemental Pollination

The pollination mechanism of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) was studied. Pollen stained five different colors and applied to the same conelets at five different times showed that the pollen applied on the 1st and 3rd days after conelets became receptive was taken into the micropyle in significantly greater quantities than pollen applied at later dates. A second supplemental pollination did not increase the seed efficiency for individual cones. Seeds produced when an average of less than 1.2 pollen grains were taken into the micropyle had essentially the same germination percentage and proportion of abnormal germinants as seeds resulting when an average of 3.4 or more pollen grains were taken into the micropyle.

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.

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