Abstract
The structure of the gynoecium and pollen tube pathway in unpollinated and pollinated carpels of Asclepias exaltata L. has been characterized. Pollen tubes penetrate a dry-type stigma, grow intercellularly in a core of solid tissue in the upper style, and subsequently traverse a hollow stylar canal to the ovary where they grow across the placental epithelium to the ovule micropyles. The fine structural characteristics of transmitting cells of the solid style, stylar canal, and placental epithelium indicate a secretory function. Extracellular secretions staining positively for proteins, insoluble carbohydrates, and arabinogalactans/arabinogalactan proteins are present in the solid style, hollow stylar canal, ovary, and micropyle. Micropylar exudate is present subtending the extended cuticle of the embryo sac adjacent to the filiform apparatus of the synergids, providing ultrastructural evidence for a secretion arising from the angiosperm embryo sac.
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References
Brown R (1833) On the organs and mode of fecundation in Orchideae and Asclepiadeae. Trans Linn Soc (Lond) 16:685–745
Broyles SB, R Wyatt (1993) The consequences of self-pollination in Asclepias exaltata, a self-incompatible milkweed. Am J Bot 80:41–44
Bruun L, Olesen P (1989) A structural investigation of the ovule in sugar beet, Beta vulgaris: the micropylar nucellus. Nord J Bot 9:81–87
Chao CY (1971) A periodic acid-Schiff's substance related to the directional growth of pollen tube into embryo sac in Paspalum ovules. Am J Bot 58:649–654
Christ VP, Schnepf E (1988) Zur Struktur und Funktion von Asclepiadaceen-Nektarien. Beitr Biol Pflanz 63:55–79
Corry TH (1883a) On the mode of development of the pollinium in Asclepias cornuti Decaisne. Trans Linn Soc Lond Ser 2 Bot:75–84
Corry TH (1883b) On the structure and development of the gynostegium and the mode of fertilization in Asclepias cornuti Decaisne (A. syriaca L.) Trans Linn Soc Lond Ser 2 Bot: 173–207
Endress PK (1980) Ontogeny, function and evolution of extreme floral construction in Monimiaceae. Plant Syst Evol 134:79–120
Endress PK (1982) Syncarpy and alternative modes of escaping disadvantages of apocarpy in primitive angiosperms. Taxon 3:48–52
Fisher DB (1968) Protein staining of ribboned epon sections for light microscopy. Histochemie 16:92–96
Franssen-Verheijen MAW, Willemse MTM (1993) Micropylar exudate in Gasteria (Aloaceae) and its possible function in pollen tube growth. Am J Bot 80:253–262
Galil J, Zeroni M (1965) Nectar system of Asclepias curassavica. Bot Gaz 126:144–148
Gurr E (1965) The rational use of dyes in biology. Hill, London
Heslop-Harrison J, Shivanna K (1977) The receptive surface of the angiosperm stigma. Ann Bot 41:1233–1238
Heslop-Harrison Y, Heslop-Harrison J, Reger BJ (1985) The pollen-stigma interaction in the grasses. 7. Pollen-tube guidance and the regulation of tube number in Zea mays L. Acta Bot Neerl 34:193–211
Jensen WA (1962) Botanical histochemistry: principles and practice. Freeman, London
Kaul V, Rouse JL, Williams EG (1986) Early events in the embryo sac after intraspecific and interspecific pollinations in Rhododendron kawakamii and R. retusum. Can J Bot 64:282–291
Kephart SR (1981) Breeding systems in Asclepias incarnata L., A. syriaca L., and A. verticillata L. Am J Bot 68:226–232
Kevan PG, Eisikowitch D, Rathwell B (1989) The role of nectar in the germination of pollen in Asclepias syriaca L. Bot Gaz 150:266–270
Knox RB (1984) Pollen-pistil interactions. Annu Rev Plant Physiol 17:508–608
O'Brien TP, McCully ME (1981) The study of plant structure: principles and selected methods. Termarcarphi, Victoria, Australia
Plotnikova T (1938) An experiment in self-pollination of Asclepias cornuti (in Russian, English summary). Ukrains'ka Akademiia nauk, Inst Bot Zh 26–27
Queller DC (1985) Proximate and ultimate causes of low fruit production in Asclepias exaltata. Oikos 44:373–381
Reger BJ, R Chaubal, R Pressey (1992) Chemotropic responses by pearl millet pollen tubes. Sex Plant Reprod 5:47–56
Reynolds ES (1963) The use of lead citrate at high pH as an electron opaque stain in electron microscopy. J Cell Biol 17:208–212
Sage TL, Broyles SB, Wyatt R (1990) The relationship between the five stigmatic chambers and two ovaries of milkweed (Asclepias amplexicaulis sm.) flowers: a three-dimensional assessment. Isr J Bot 39:187–196
Sanders LC, Lord EM (1992) A dynamic role for the stylar matrix in pollen tube extension. Int Rev Cytol 140:297–318
Schnepf E, Christ P (1980) Unusual transfer cells in the epithelium of the nectaries of Asclepias curassavica L. Protoplasma 105:135–148
Sparrow FK, Pearson NL (1948) Pollen compatibility in Asclepias syriaca. J Agric Res 77:187–199
Spurr AR (1969) A low-viscosity epoxy resin embedding medium for electron microscopy. J Ultrastruct Res 26:31–43
Staehelin LA, Chapman RL (1987) Secretion and membrane recycling in plant cells: novel intermediary structures visualized in ultrarapidly frozen sycamore and carrot suspension-culture cells. Planta 171:43–57
Stevens OA (1945) Cultivation of milkweeds. N D Agric Exp Stn Bull 333:1–19
Tilton V (1980) The nucellar epidermis and micropyle of Ornithogalum caudatum (Liliaceae) with a review of these structures in other taxa. Can J Bot 58:1872–1884
Webb MC, Williams EG (1988) The pollen tube pathway in the pistil of Lycopersicon peruvianum. Ann Bot 61:415–423
Wyatt R (1976) Pollination and fruit-set in Asclepias: a reappraisal. Am J Bot 63:845–851
Wyatt R, Broyles SB (1994) Ecology and evolution of reproduction in milkweeds. Annu Rev Ecol Syst 25:423–441
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Sage, T.L., Williams, E.G. Structure, ultrastructure, and histochemistry of the pollen tube pathway in the milkweed Asclepias exaltata L.. Sexual Plant Reprod 8, 257–265 (1995). https://doi.org/10.1007/BF00229381
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DOI: https://doi.org/10.1007/BF00229381