1,721,098 research outputs found
Lythrum salicaria pollen and pistil cytomorphology
No full textVengono riportati i risultati di una ricerca sulla citomorfologia di polline e pistillo in Lythrum salicari
Harmomegathy in heteranteric species
No full textHarmomegathy was described in five heterantheric species. The harmomegatic mechanism was evidentiated "in vitro" using solutions at different sucrose concentration
Total polysaccharide content of developing pollen in two angiosperm species.
No full textTotal polysaccharide content of developing pollen in two angiosperm species has been investigate
Cupressus arizonica pollen wall zonation and in vivo hydration
No full textThe structure of Cupressus arizonica
pollen at different degrees of hydration was examined
by using cytochemical staining and light (LM) and
scanning electron (SEM) microscopy. Most pollen
grains are inaperturate and a minority are provided
with an operculate pore enveloped by a concave
annulus. Intine consists of: 1) a thin polysaccharidic
outer layer, 2) a large polysaccharidic middle layer
that is spongy and bordered by a mesh of large and
branched fibrils, and 3) an inner cellulosic thick layer
with callose concentrated on the inner side, which
forms a shell around the protoplast. The protoplast is
egg-shaped with PAS positive cytoplasm and prominent
nucleus. Exine splits during hydration and is cast
off according to three major steps: 1) the split opens
like a mouth and the underlying intine is expelled by
swelling like a balloon, 2) the protoplast enveloped by
the inner intine is sucked in the outgrowing side, and
3) the backside of the intine gets rid of the exine shell.
In water containing salts, exine is rapidly released and
the middle intine may expand up to break the outer
layer, with disgregation of the spongy material and
release of the intine shell including the protoplast. In
water lacking salts, the sporoderm hydration and
breaking are negatively influenced by the population
effect. Pollen when air dried after the exine release
become completely flat owing to disappearance of the
middle intine layer which may be restored by dipping pollen in water. The results are discussed in relation to
the functional potentialities of the sporoderm
Effect of pistil age on pollen tube growth, fruit development and seed set in Cucurbita pepo L.
No full textThe effects of pistil age on pollen tube growth, fruit development and seed set were studied in Cucurbita pepo L., the flower of which opens for only six hours. Stigma receptivity lasts four days, from one day before until two days after anthesis. Style receptivity lasts three days, from the day before to the day after anthesis. Ovule receptivity lasts two days: the day of anthesis and the day before. The rate of pollen tube growth varies in different parts of the pistil and in relation to pistil age. In the stigmatic and stylar region, the tubes grow faster if pollination occurs the day before anthesis; in the ovary they grow faster when pollination occurs at anthesis. In the receptacle region, where the transmitting tissue is reduced, the growth rate decreases independently of the time of pollination. The fruits are larger and heavier with more seeds when pollination occurs at anthesis. There is a positive correlation between seed number and fruit weight when pollination occurred at anthesis and the day before
Nectar production and presentation
No full textNectar secretion is complicated to study from the ultrastructural point of view because it is a dynamic process involving many tissues simultaneously. Study may also be affected by artefacts created by chemical fixation procedures, although this problem can be overcome by freeze-drying and freeze substitution techniques (Zhu & Hu, 2002; Stpiczyńska et al., 2005b). Previous research has focused on the ultrastructure of secretory cells, especially secreting trichomes (Robards & Stark, 1988), and a general model of nectary function as a whole is still lacking. © 2007 Springer. All rights reserved
Some cytological, ecological and evolutionary aspects of pollination
No full textDifferent types of pollen dispersing units are described. The pollen of angiosperms may be dispersed in monads, tetrads, polyads, massulae or compact pollinia. The monads and tetrads may form larger clumps of pollen with the aid of the following substances: a) pollenkitt, a product of in situ degeneration of the tapetum; b) tryphine, a product of tapetal extra situm degeneration, found only in Cruciferae; c) elastoviscin, a highly viscous product of the degeneration of a limited number of tapetal cells, found only in certain Orchidaceae; d) viscin threads or sporopollenin filaments arising from the pollen exine. The number of pollen grains composing the clumps depends on pollen diameter and the cohesive forces holding the pollen grains together. The various types of pollen dispersing unit are discussed in relation to the type of pollination and number of ovules per ovary
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