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The reproductive biology of Totara (Podocarpus totara) (Podocarpaceae)

Author:
Wilson, V.R., Owens, J.N.
Source:
Annals of botany 1999 v.83 no.4 pp. 401-411
ISSN:
0305-7364
Subject:
fertilization (reproduction), sexual reproduction, phenology, dormancy, ovules, pollination, pollen tubes, ova, degradation, cytoplasm, cell walls, plant anatomy, histology, ultrastructure, New Zealand
Abstract:
A reproductive cycle of totara (Podocarpus totara) in New Zealand is complete within 2 years. After strobilus initiation in September, there is a 9 month period of winter dormancy until emergence during the growth flush in July-August of the following year. Female strobili bear only one or two ovules which are pollinated mid-October to mid-November at the megaspore tetrad stage. Pollen germination and fertilization occur rapidly during December. The pollen tube carries the body cell, sterile and tube nuclei with at least three prothallial nuclei, and branches out after reaching the archegonia. The four-six archegonia contain egg nuclei with no distinct perinuclear zone and a large chalazal vacuole. Fertilization by the larger of the two unequal male gametes is accompanied by a degradation of egg cell cytoplasm. The three-tier proembryo contains a binucleate embryonal tier of only one cell. Soon after embryo penetration into the megagametophyte, the binucleate embryonal-tier cell undergoes mitosis and cell wall formation resulting in four uninucleate cells. Some ovules contained secondary embryos thought to be the product of suspensor cleavage. Embryo maturation occurs by February.
Agid:
2561091