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 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.

A phenological and cytological study of pollen development in western hemlock (Tsuga heterophylla)

1988 ◽  
Vol 66 (5) ◽  
pp. 907-914 ◽  
Author(s):  
Anna M. Colangeli ◽  
John N. Owens
Keyword(s):  
Cell Division ◽  
Pollen Grains ◽  
Tsuga Heterophylla ◽  
Western Hemlock ◽  
Bud Burst ◽  
Cone Development ◽  
Tube Cell ◽  
The One ◽  
Pollen Cone ◽  
Stage 1

Pollen-cone development, which was divided into nine phenological stages, was compared with pollen cytology in eight field-grown western hemlock (Tsuga heterophylla (Raf.) Sarg.) clones in 1983 and three container-grown clones in 1984. Phenology proved to be an accurate indicator of cytology, independent of collection dates and rate of development. The breaking of dormancy, the resumption of development, and meiosis occurred during stage 1 (quiescent bud). During stage 2 (swollen pollen-cone bud) the tetrad of microspores separated. The exine wall was completely developed during stage 3 (bud burst). The one-celled microspores began to expand as a result of accumulation of reserves during stage 4, when the pollen cones were one-quarter to one-half emerged through the bud scales. The first cell division occurred during stage 5, when the cones were greater than half emerged. The second and third cell divisions occurred during stage 6, after the cones had completely emerged through the bud scales. The fourth and final cell division, resulting in mature five-celled pollen grains occurred during stage 7 (stalk elongation). Mature pollen consisted of two prothallial cells and a stalk, a body, and a tube cell. Pollen shed occurred at stage 8. The empty cones (stage 9) remained on the trees until the following winter. Some practical implications of relating pollen-cone phenology to cytology are discussed.

Promotion of flowering in western hemlock by gibberellin A4/7 applied at different stages of bud and shoot development

1989 ◽  
Vol 19 (8) ◽  
pp. 1051-1058 ◽  
Author(s):  
John N. Owens ◽  
Anna M. Colangeli
Keyword(s):  
Effective Treatment ◽  
Shoot Elongation ◽  
Shoot Development ◽  
Western Hemlock ◽  
Bud Burst ◽  
Cone Production ◽  
Seed Cone ◽  
Pollen Cone ◽  
Vegetative Bud

Cone buds were induced on container-grown and field-grown western hemlock (Tsugaheterophylla (Raf.) Sarg.) clones during a 3-year period to study the effects of time and duration of gibberellin A4/7 treatment on cone induction, sexuality of cones, and to relate these results to bud and shoot development. The most effective treatment times preceded anatomical differentiation. The most abundant pollen cones and seed cones were produced when trees were sprayed with gibberellin A4/7 before vegetative bud burst and early shoot elongation. Two to three weekly gibberellin A4/7 applications starting at preswollen and swollen-bud stages were adequate for pollen-cone production. Pollen-cone production decreased when the applications were started at vegetative bud burst or during early shoot elongation. A minimum of three weekly applications were required for seed-cone production, and applications were equally effective when started at preswollen, swollen, and vegetative bud burst stages. Seed-cone production decreased when three weekly applications were started during early shoot elongation; however, this was overcome by increasing the number of applications.

Pollen morphology and development of the pollination mechanism in Tsuga heterophylla and T. mertensiana

1983 ◽  
Vol 61 (12) ◽  
pp. 3041-3048 ◽  
Author(s):  
John N. Owens ◽  
Margaret Dianne Blake
Keyword(s):  
Reproductive Biology ◽  
Pollen Morphology ◽  
Pollen Tubes ◽  
Tsuga Heterophylla ◽  
Western Hemlock ◽  
Pollination Mechanism ◽  
Pollination Drop ◽  
Tsuga Mertensiana

Pollen of Tsuga heterophylla (Raf.) Sarg. (western hemlock) is nonsaccate and bears spines, whereas pollen of Tsuga mertensiana (Bong.) Carr. (mountain hemlock) is saccate and lacks spines. The pollination mechanism in western hemlock consists of a short funnel-like integument tip with a large micropyle. Pollen may enter the micropyle or germinate on the bract or ovuliferous scale and form long pollen tubes. The pollination mechanism in mountain hemlock consists of two large micropylar flaps which secrete minute droplets to which pollen adheres. A pollination drop is not formed in either species. These features are discussed in relation to the taxonomy of the genus and the reproductive biology of these two species.

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 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 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.

The pollination mechanism of Abies amabilis

2004 ◽  
Vol 34 (5) ◽  
pp. 1071-1080 ◽  
Author(s):  
Luke M Chandler ◽  
John N Owens
Keyword(s):  
Electron Microscopy ◽  
Epicuticular Wax ◽  
Pollination Mechanism ◽  
Abies Amabilis ◽  
Cone Axis ◽  
Inner Surface ◽  
Pollination Drop ◽  
And Function ◽  
Scale Surface ◽  
Scanning Electron

The development and function of the pollination mechanism were studied in Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes growing in clonal seed orchards. Two adaxial ovules developed on each scale after dormancy and each ovule formed a funnel-like integument tip with a nucellus at the base of the shallow funnel. At receptivity, the seed cones were erect and the ovules inverted. No pollination drop was observed in fresh specimens but lipid microdrops were secreted on the rim and inner surface of the funnel. Water applied as spray beaded on all cone surfaces except where microdrops were present. Surfaces of the cone were observed using scanning electron microscopy to determine the presence and ultrastructure of the waxy cuticle. All surfaces that were not wettable with water were covered with epicuticular wax. Pollen did not adhere firmly to cone surfaces having epicuticular wax but adhered to the microdrops on the funnel. Drops of water picked up pollen as they moved over the waxy surfaces toward the cone axis. There, the inverted ovules were arranged in a tight helix around the cone axis. Beads of water, often containing pollen, settled on the scale surface just below the funnels and then touched and wetted the inside of the funnels, forming a column of water from the scale surface below to the funnel above. The saccate, buoyant pollen then floated up and into the funnel. Experiments were done to determine the effect of pollen application on pollen uptake into the ovule: without water, with water applied before or after pollen was applied, or as a pollen–water mix. Results support the hypothesis that A. amabilis, and likely other Abies species, lacks a conspicuous pollination drop and water as rain or dew substitutes for a pollination drop.

Cone and seed development in a wind-pollinated, western hemlock (Tsugaheterophylla) clone bank

1990 ◽  
Vol 20 (9) ◽  
pp. 1432-1437 ◽  
Author(s):  
Anna M. Colangeli ◽  
John N. Owens
Keyword(s):  
Seed Production ◽  
Seed Yield ◽  
Western Hemlock ◽  
Factors Affecting ◽  
Ovule Abortion ◽  
Cross Pollination ◽  
Seed Cone ◽  
Cone Development ◽  
Empty Seed ◽  
Pollen Cone

Seed and seed-cone development were observed in a wind-pollinated western hemlock (Tsugaheterophylla (Raf.) Sarg.) clone bank in 1983 and 1986. Seed efficiency, the number of filled seed per cone divided by the seed potential, averaged 64% for 58 wind-pollinated clones in 1983 and 20% for 38 clones in 1986. Based on anatomical observations and cone dissections, seed losses resulted from pre- and post-pollination ovule abortion, insufficient pollen, no fertilization, and embryo degeneration. Prepollination ovule abortion, identified by small, flat seed in mature cones, contributed to 11 and 14% reduction in filled-seed yield in 1983 and 1986, respectively. Full-sized but empty seed (lacking an embryo) accounted for 25 and 66% reduction in potential seed yield in the 2 years, respectively. In 1983, 98% of the clones bore a pollen-cone crop compared with 53% in 1986. Lack of fertilization resulting from a limited pollen supply was believed to be the main cause for the lower filled-seed yield in 1986. The effect of wind and controlled (cross-) pollination on filled-seed production was determined for 16 clones in 1983. Seed efficiency after wind and cross-pollination averaged 65 and 69%, respectively. Seed potential averaged 34 and 31 ovules per cone for the wind- and cross-pollinated cones, respectively. Prepollination ovule abortion averaged 12 and 14%, respectively. From anatomical observations, the full-sized but empty seed resulted from lack of fertilization and embryo degeneration. The different factors affecting final filled-seed yield are discussed in terms of their effect on seed production.

Immunolocalization of H+-ATPases in the plasma membrane of pollen grains and pollen tubes ofLilium longiflorum

PROTOPLASMA ◽  
1992 ◽  
Vol 171 (1-2) ◽  
pp. 55-63 ◽  
Author(s):  
G. Obermeyer ◽  
M. L�tzelschwab ◽  
H. -G. Heumann ◽  
M. H. Weisenseel
Keyword(s):  
Plasma Membrane ◽  
Pollen Grains ◽  
Pollen Tubes
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