Pollen grains, development

A typical palynological study might involve the collection of one or more cores of sediment or peat from a site. The layers occurring at various depths would be dated, and samples of the pollen grains contained in the layers would be extracted, classified, and enumerated. From the dated fossil pollen of various species or genera, the palynologist would develop inferences about the nature of the forests and other plant communities that may have occurred in the local environment at the time. 

Pollen germination and pollen tube growth have been used as end points. Pollen grains from a number of plants have been used, and an assay for growth of pollen from Nicotiana sylvestris has been developed (Kristen and Kappler 1995). 

In the more benign asexual cycle, Epichloe endophytes (and all Neotyphodium species) remain asymptomatic (Fig. 1). As floral primordia are formed, endophytes grow into ovules, proliferate in the nucellus tissues, and later colonize the embryonic axis of the developing seed, which leads to vertical transmission (Freeman, 1904 Philipson and Christey, 1986). Hyphae in the remnant nucellar layer form a conspicuous mat between the aleuron and the seed coat (White et al., 1991). Symptomless endophytes may also invade stamen filaments and anther walls, but have never been found in pollen grains, and apparently are not disseminated via paternal structures (Sampson, 1933 Hinton and Bacon, 1985). Vertical transmission of endophytes in infected tillers occurs at nearly 100% efficiency (Siegel et al., 1984). However, seeds which are free of endophyte may occasionally be produced when shoot meristems of individual... 

Microspores are the precursors of the male gametes of plants and are equivalent to spermatids of animals. Microspores develop into pollen grains within the anthers of a flower in angiosperms. Mature pollen grains are the male gametophytes. The function of the male gametophyte is to participate in the sexual reproduction of plants. 

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