Wet Stigma Research Articles

Nonrandom mating inDiscaria americana (Rhamnaceae)

Nonrandom mating takes place when seed paternity differs from that produced by random success of available pollen. To test if some form of this phenomenon operates in the self-incompatible perennialDiscaria americana, we performed one-donor hand pollinations involving seven individuals, and measured pollen-tube performance and seed viability and germination. A significant level of heterogeneity in reproductive traits was present in our sample. Mating was nonrandom as a consequence of complete self-incompatibility (intrafloral and geitonogamous pollinations were unsuccessful) linked with partial cross-compatibility (some inter-individual pollinations consistently failed to produce offspring while other parental combinations were fecund). Pollen tubes of successful pollen parents exhibited higher growth rate than those of infecund ones. Stylar-ovarian inhibition of incompatible pollen tubes and a wet stigma type suggests that a gametophytic incompatibility system operates in the species.

A scanning electron microscope study of the pollen tube pathway in pistils of Rhododendron

The pollen tube pathway was observed at regular intervals in pistils of four species of Rhododendron, with emphasis on Rhododendron fortunei. Rhododendron is characterized by a nonpapillate wet stigma, angled stylar canal, placentae with central clefts, and many unitegmic anatropous ovules. Receptive stigmas were hand-pollinated with self pollen 1 – 8 days after anthesis. The pollen, which occurs in permanent tetrads, started germinating during the 1st day. After crossing the stigma surface to one of the grooves leading into the stylar canal, pollen tubes grew straight through the style, and continued into the placental clefts from which they emerged onto the placental surface to grow among the ovules. Tubes reached the ovary in 5 – 10 days depending on the species and took several days after entering the upper ovary to reach the base of the placentae. Single tubes (rarely two or more) diverged from the interovular network and grew under the integument (which is close against the placental surface) to enter the slit-like micropylar opening of an ovule. The morphology of the micropylar slit and the direction of pollen tube entry showed variation among ovules. In R. fortunei ovule entries occurred first on the upper half of the placenta, though not at the top, and in ovules closest to the placental cleft. All portions of the pathway, from stigma surface to micropylar opening, are covered by exudate. Stigmatic exudate increased in amount and became more viscous after pollination, burying the pollen grains and tubes, then gradually dried. Exudate was produced in the style and ovary whether or not pollination occurred. Characteristics of the pollen tube pathway in Rhododendron are discussed relative to those in other angiosperm taxa. Key words: Rhododendron, pollen–pistil interactions, fertilization, transmitting tissues, pistil exudates, ovule entries.

POLLEN‐PISTIL INTERACTIONS IN TRISTYLOUS PONTEDERIA SAGITTATA (PONTEDERIACEAE). I. FLORAL HETEROMORPHISM AND STRUCTURAL FEATURES OF THE POLLEN TUBE PATHWAY

Heteromorphic characters and structural features of the pollen tube pathway are described in tristylous Pontederia sagittata to assess their influence on the pollination process and in mediating self‐incompatibility behavior. Heteromorphic characters that distinguish the floral morphs include style length, stigma depth, stigmatic papillae length, stylar parenchyma cell length, area of the stylar canal, stamen height, anther size, and pollen size. Unlike several distylous species that have been investigated, the exine of pollen in P. sagittata was not strongly differentiated among the pollen types, and no differences in stigma cytochemistry were apparent. Features common to the floral morphs were a wet stigma, a hollow trilobed stylar canal separating into two sterile and one fertile canal, and a single anatropous ovule with a highly elaborated integumentary obturator. The similarity in structural features of the pollen tube pathway of P. sagittata to those found in monocotyledonous taxa with gametophytic self‐incompatibility suggests that phylogenetic constraints may have influenced the evolution of trimorphic incompatibility in the Pontederiaceae.

Calcium uptake from the stigma by germinating pollen in Primula officinalis L. and Ruscus aculeatus L.

The flow of calcium ions from the stigma to germinating pollen was studied by autoradiography in Primula officinalis (dry stigma) and Ruscus aculeatus (wet stigma). 45Ca2+ ions were observed to be taken up by the pistils from an agar medium and then transported intracellularly to both the stigmal cells and the stigmal exudate. The 45Ca2+ present in the stigma was taken up by the germinating pollen grains.

Steps Toward a Natural System of the Dicotyledons

Embryological character states are mapped on the diagrams of dicotyledons (G. Dahlgren 1989). The often well-defined pattern of distribution forms a basis for discussing and clarifying phylogenetic relations. It is shown how numerous embryological characters, alone or in combinations, support certain systematic constellations, even if the character states may have arisen independently within a varying number of evolutionary lines. Characters presented are: anther wall formation; tapetum types; cells in pollen grains at dispersal; microsporogenesis; ovule morphology; ovule integuments; endothelium; obturator; parietal tissue; embryo sac formation; antipodal cells; hypostase, embryogeny; polyembryony; endosperm formation; persistence of endosperm; ruminate endosperm; endosperm haustoria; perisperm; storage compounds in the endosperm; chlorophyllous embryo; embryo size, seed coat characters; arils; dry and wet stigma types.

Floral Morphology of Eucalyptus melliodora A. Cunn. ex Schau. And Comparisons With Other Eucalypt Species

The important phases of floral development in E. melliodora from bud initiation to anthesis and style abscission are documented by means of scanning electron micrographs. Thirteen phases of bud development from first indication of operculum abscission to style abscission are presented, as well as the timing and duration of each phase. Anther dehiscence commences prior to flower opening and no pollen grains were observed on flowers 2 days after opening. Secondary transportation of pollen after deposition is possible. Nectar secretion did not commence until after pollen was shed and the stigma became receptive. Although individual flowers were protandrous, there was some overlap within a single inflorescence between pollen shed and the 'wet stigma' phase, suggesting that geitonogamy was possible. The style did not increase in length following anthesis, a common feature in Eucalyptus, leaving the stigma in close proximity with the anthers. There was a graduation in filament length from the outer to inner whorls. The innermost anthers produced the most pollen grains while the outermost were staminodal. There was considerable difference between the number of stamens (71-312), staminodes (0-83) and pollen grains per anther (643-1790) found in the six species examined. Stamen length in all species increased across the staminophore from 1.82-6.99 mm in the inner whorl to 4.84-12.61 mm in the outer whorl.

The Stigma of Dendrobium speciosum Sm. (Orchidaceae): A New Stigma Type Comprising Detached Cells Within a Mucilaginous Matrix

The stigma of Dendrobium speciosum does not correspond to any morphological category previously described. The stigma lies on the lower surface of the column as an oval, bowl-shaped depression containing a wet, jelly-like, viscid material, which comprises a large number of elongated, detached cells suspended in a matrix. The stigmatic cells are thick walled and have a vacuolated cytoplasm containing amyloplasts. These cells give a positive reaction to fluorescein diacetate indicating that the plasma membrane is intact; this evidence points to the conclusion that the stigmatic cells are not detached, senescent or necrotic papillae. Histochemical staining of the matrix shows high levels of acidic polysaccharides with low levels of lipids and proteins. Biochemical analysis shows this matrix to comprise around 80 per cent uronic acids. This highly specialized stigma may be a further evolutionary development of the wet papillate stigma resulting from the special needs of both pollination and the nutritional support of the large number of developing pollen tubes.

Stigma, Style, and Obturator of Soybean, Glycine Max (L.) Merr. (Leguminosae) and Their Function in the Reproductive Process

Soybeans have a wet stigma overtopped by a pellicle that originates from the cuticle. There are numerous exudate-filled, axially oriented channels between cells of the transmitting tissue in the stigma and style. Pollen tubes grow in these channels and receive nutrition and mechanical guidance. Transmitting-tissue cells of the obturator are secretory also, but the obturator in soybean does not appear to control direction of pollen tube growth mechanically. The significant function of transmitting tissue in soybeans is to provide nutrition and to control direction of pollen tube growth.

STIGMA, STYLE, AND OBTURATOR OF SOYBEAN, GLYCINE MAX (L.) MERR. (LEGUMINOSAE) AND THEIR FUNCTION IN THE REPRODUCTIVE PROCESS

Soybeans have a wet stigma overtopped by a pellicle that originates from the cuticle. There are numerous exudate‐filled, axially oriented channels between cells of the transmitting tissue in the stigma and style. Pollen tubes grow in these channels and receive nutrition and mechanical guidance. Transmitting‐tissue cells of the obturator are secretory also, but the obturator in soybean does not appear to control direction of pollen tube growth mechanically. The significant function of transmitting tissue in soybeans is to provide nutrition and to control direction of pollen tube growth.

Stigma-surface Esterase Activity and Stigma Receptivity in Some Taxa Characterized by Wet Stigmas

Stigma-surface esterase activity and stigma receptivity through a sequence of developmental stages of the pistil have been studied in four taxa characterized by having wet stigmas-Petunia hybrida, Nicotiana tabacum, Crinum defixum and Amaryllis vittata. The style is solid in the first two and hollow in the latter two taxa. In all the taxa, stigma-surface esterase could be detected in a thin surface layer (pellicle) from a very early stage of pistil development, irrespective of the presence or absence of the exudate. However, the taxa showed variation in stigma receptivity. In Petunia and Nicotiana, stigmas from pistils of all the stages supported pollen germination and tube growth. In Amaryllis and Crinum, stigmas of only the mature pistils, when the exudate is present on the stigma, supported normal pollen germination and tube growth. It is inferred that in taxa characterized by a wet stigma and solid style, the factors required for pollen germination are present from an early stage of pistil development and the exudate per se is not involved in pollen germination. In taxa characterized by a wet stigma and hollow style, however, the pellicle does not carry the factors required for pollen germination and tube growth; they appear to be present in the exudate.

走査型電子顕微鏡による温州ミカン南柑4号の花器および幼葉の外部形態の特性

Morphological features of the surfaces of juvenile leaves, flowers and young developing fruits were examined with a clone of satsuma mandarin (Nankan No. 4) by scanning electron microscopy. The surface of unpollinated stigma was covered with a number of mature and immature papiliary cells. The stigma of satsuma mandarin, being classified in the ‘wet stigma’ category, excreted some mucilaginous substances at the base of papillary cells even before pollination.Normal anthers consisted of four lobes of which the epidermal layers were creased, giving an appearance of much wrinkled surface. The distance between two adjacent grooves on the anther surface was about 20μm. Mature anthers were fairly swollen and the lobe junctions were somewhat grooved, whereas immature ones were tapered at their tips. Filaments were united with one another at their bases, thus forming ‘fasciated stamens’.Oblong epidermal cells of the petals were about 15μm wide and oriented regularly in the longitudinal direction. The longitudinal junction of adjacent epidermal cells was clearly defined under the microscope. The transverse junction, however, was more or less indistinct because of gradual transition from one cell to another.Accompanied by greening of the ovary rind, stomata were formed in its epidermal tissues. The stomatal areas of the rind consisted of 2 guard and 6 to 7 subsidiary cells. These areas were raised above the epidermal surface of surrounding areas. In the juvenile stage, the epidermal cells of fruits were oriented regularly in the longitudinal direction though they became irregular with the progress of time.In juvenile leaves, however, large-sized solitary stomata (giant stomata) surrounded by a number of normal-sized ones were dispersed sporadically all over the surface. Unlike the young fruit, stomatal areas were not raised above the leaf surface.