Stigmatic Morphology of Chinese Chestnut (Castanea mollissima Blume)

The stigmatic morphology of Chinese chestnut was studied with scanning electron microscopy. The stigma is typically needle-shaped with a small aperture ≈50 μm in diameter on the top. During late April and early May in Yunnan Province, China, stigma secretion begins and within 1 week, secretion increases quickly and completely covers the stigma aperture. In “high fruit load” trees, the stigma aperture appears larger than in “low fruit load” trees, which in turn have a larger aperture than “empty cupule” trees. Likewise, stigma secretion in female flowers on “high fruit load” trees was higher than “low fruit load” or “empty cupule” trees.

Reproduction in seagrasses: pollination in Amphibolis antarctica

Pollination in the dioecious marine angiosperm Amphibolis antarctica has been studied in plants maintained in constant conditions. When the ripe filiform pollen is applied to the submerged stigmas, the grains adhere tenaciously to the receptive zones of the branches. Microsopical examination of the stigmas at this stage shows that a meniscus is developed at each point of pollen-stigma contact and that in every case this results from local coalescence of a proteinaceous substance coating the grain wall and a film of secretion product on the surface of the stigma. Once the grains are attached to the stigma, pollen germination begins. At the site of the future germinal aperture a small region of the pollen wall fabric is gelatinized, presumably by glycosidase activity. At the same time as this process, or shortly afterwards, a lens of polysaccharide is deposited beneath the incipient aperture. The lens hydrates and extrudes, pushing the lax region of wall outwards to form a surface papilla. Extension is limited and the apertural perforation originates when the degraded wall fabric in the distal region of the papilla finally disperses. The pollen tube then emerges through the aperture and rapidly grows towards the stigma, the tube tip eventually making contact with the secretion layer. Entry of the tube into the stigma requires enzymic erosion of the stigma cuticle, and esterases contained in the stigma secretion are probably implicated in the process, but penetration was not directly observed. None the less, cuticle lysis must occur because some hours after pollen attachment pollen tubes are seen in the epidermal tissue of the stigma branch and growing towards the ovary. The principal features of the seagrass pollination system are compared with their counterparts in the pollination system of the land-based flowering plants, and the comparisons reveal marked similarities as well as differences between them.

Anatomy of the Unpollinated and Pollinated Watermelon Stigma

The structure of the watermelon stigma before and after pollination was studied using light and electron microscopy, freeze-fracture and autoradiography. The wall thickenings of the papilla transfer cells contained callose and their presence prior to pollination was confirmed using EM-autoradiography, freeze-fracture and fixation. No further callose thickenings were produced following pollination. Pollination resulted in a rapid increase in aqueous stigma secretion and localized disruption of the cuticle, which appeared to remain on the surface of the secretion. Autolysis of the papilla cells, which had commenced prior to pollination, was accelerated and appeared to take place via cup-shaped vacuoles developed from distended endoplasmic reticulum. The reaction was localized to the papilla cells adjacent to the pollen tube only. Both pollen-grain wall and stigma secretion contained proteins, carbohydrates, acidic polysaccharides, lipids and phenolics.

Ultrastructure and histochemistry of the watermelon stigma

The ultrastructure and histochemistry of the watermelon stigma were followed from 6 days before flower opening to anthesis. Starch and lipid were present in the immature papilla cells but had largely disappeared from the cells by anthesis, when carbohydrate and lipid were present in the stigma secretion external to the cell wall. Th mature papilla cells had simple wall thickenings and were transfer cells. The wall thickenings were associated with dictyosomes and secretory vesicles. Other characteristics indicating a secretory function for the papilla cells included plastid-ER complexes and close associations between ER and secretory vesicles at the plasmalemma. Granulocrine secretion involving dictyosomes and ER is suggested for the carbohydrate component of the secretion.

Structural changes in the pollinated and unpollinated avocado stigma and style

Structural changes in the pollinated and unpollinated avocado (Persea americana Mill) stigma and style up to 42 h after first opening of the flower were investigated using light and electron microscopy. The pollen tubes grew in the stigma secretion and intercellular substance and initial contact occurred between the plasma membrane of the male and the cuticle and stigma secretion of the female. The pollen tube wall started to develop 15 min after pollination and increased in thickness up to 24 h after pollination. By 18 h after first opening of the flower, starch had disappeared and cell wall thickenings were present in both the pollinated and unpollinated stigma and style. The wall thickenings developed more slowly in the unpollinated than in the pollinated tissue. They contained lipid and were bounded by callose. Degeneration of the cytoplasm of some of the papilla and transmitting tissue cells occurred only following the passage of the pollen tubes and may be of importance in tube nutrition. There was no degeneration in the unpollinated stigma and style and the cytoplasm did not start to lose clarity until 42 h after first opening of the flower.

Structure of the Stigma and Style of the Avocado

The structure of the stigma and style of the avocado (Persea americana Mill.) was investigated by light microscopy, scanning electron microscopy and transmission electron microscopy of thin sections and freeze-fracture replicas. The stigmalstyle was asymmetrical and a groove, lined with transmitting tissue, extended the whole length of the structure. Stigma papillae fringed this groove for about a third of its length. There was no clear distinction between stigma papillae and stylar transmitting tissue cells but there was a gradation of structure down the axis. The papilla cells were long with large and small vacuoles; the transmitting tissue cells had small vacuoles only. The stigma secretion and intercellular substance of the transmitting tissue contained carbohydrate and lipid. Clusters of plastids with little internal structure and electron-dense stroma were abundant in the cells of the stigma and transmitting tissue along with extensive smooth endoplasmic reticulum. Both single vesicles and multivesicular bodies were observed fusing with the plasmalemma which was abnormally rough in freeze-fracture profiles. It is suggested that the cells of the stigma and transmitting tissue have a largely secretory function and may be approaching or have reached senescence when the flower opens.