Microsporogenesis, Pollination, Pollen Germination and Male Gametophyte Development in Taxus brevifolia

Taxus brevifolia(Nutt.), commonly known as Pacific or westernyew, is a conifer native to the Pacific northwest of North America.Contrary to other Taxus species, T. brevifolia staminate strobiliare usually located on 2-year-old foliage although they mayoccur on foliage from 1 to 5-years-old. This delayed staminatestrobilus development may be an adaptation to the low lightenvironment where T. brevifolia grows. Microsporogenesis occurredin the autumn preceding pollination. Successive divisions producedisobilateral tetrads visible as early as mid-October. Over-winteringstaminate strobili usually contained separate microspores. In1996 to 1999, pollination occurred in March and April in twonatural forest sites on southern Vancouver Island, British Columbia,Canada. The low amounts of airborne pollen and prolonged pollinationperiod indicated low pollination success within T. brevifolia.Female receptivity was measured by the presence of a pollinationdrop. Protandry up to 18 d was observed. In vitro pollen germinationwas moderate to good, ranging from 65 to 88% depending on thetree and year. DAPI fluorescence staining showed successfulmale gametophyte development in vitro. The microspore dividedforming a tube nucleus and generative cell within 3 d of culture.The generative cell then divided forming a sterile nucleus andspermatogenous nucleus after 17 d. The spermatogenous nucleusacquired a cell wall then divided forming two equal sperm after24 d. Copyright 2000 Annals of Botany Company Taxus brevifolia, Pacific yew, microsporogenesis, pollination, pollen germination, male gametophyte development