The Mechanisms of Pollination and Fertilization in Plants

Abstract

In flowering plants, pollen grains germinate to form pollen tubes that transport male gametes (sperm cells) to the egg cell in the embryo sac during sexual reproduction. Pollen tube biology is complex, presenting parallels with axon guidance and moving cell systems in animals. Pollen tube cells elongate on an active extracellular matrix in the style, ultimately guided by stylar and embryo sac signals. A well-documented recognition system occurs between pollen grains and the stigma in sporophytic self-incompatibility, where both receptor kinases in the stigma and their peptide ligands from pollen are now known. Complex mechanisms act to precisely target the sperm cells into the embryo sac. These events initiate double fertilization in which the two sperm cells from one pollen tube fuse to produce distinctly different products: one with the egg to produce the zygote and embryo and the other with the central cell to produce the endosperm.

Remnant Pachira quinata pasture trees have greater opportunities to self and suffer reduced reproductive success due to inbreeding depression

“…Selfing can ensure reproductive success where mates are limited (by low densities or pollen movement) (Baker, 1955); however, it can lead to reduced genetic variation and offspring fitness. Outcrossing can be achieved by a complex array of mechanisms reducing self-pollination and self-fertilisation (Barrett, 1998;Lord and Russell, 2002;Hiscock and McInnis, 2003;Takayama and Isogai, 2005). Self-pollination can be limited by pre-pollination mechanisms, such as temporal and spatial separation of male and female structures, and pollinator behaviour (Barrett, 1998).…”

“…Self-pollination can be limited by pre-pollination mechanisms, such as temporal and spatial separation of male and female structures, and pollinator behaviour (Barrett, 1998). Selfincompatibility may act at various stages: blocking germination on the stigma, growth through the style, and penetration and fertilisation of the ovary (Lord and Russell, 2002;Takayama and Isogai, 2005). Neotropical trees are predominantly outcrossing, despite earlier predictions that selfing would dominate due to low tree densities in wet forests (Baker, 1959;Bawa et al, 1985;Ward et al, 2005).…”

Endosperm: an integrator of seed growth and development

“…Despite significant advances in our understanding of guidance mechanisms for the pollen tube and the transcriptional activity of the gametes [2][3][4], our knowledge on the actual mechanism of fertilization remains extremely limited. A remarkable recent study has shown, however, that the fusion between the sperm cells and the female gametes involves the conserved protein GENERATIVE CELL SPECIFIC 1 (GCS1) [5 ].…”

The COMATOSE ATP-Binding Cassette Transporter Is Required for Full Fertility in Arabidopsis

“…Pollen tubes grow at extremely high rates in vivo and consequently have a very high demand for energy (Lord, 2000;Lord and Russell, 2002). Because pollen is often in excess, tubes must compete for access to ovules; thus, rapid growth is key to male reproductive success .…”

“…Because pollen is often in excess, tubes must compete for access to ovules; thus, rapid growth is key to male reproductive success . The pollen tube is known to interact intimately with the nutrient-rich extracellular matrix of the stylar tract and adhesion factors implicated in pollen tube growth have been identified in lily (Lilium longiflorum) and tobacco (Nicotiana tabacum; Lord, 2000Lord, , 2003Lord and Russell, 2002). Pollen tube growth and guidance are separable genetically , but the identities of diffusible signals directing pollen tubes to the ovules and ultimately permitting entry to the micropyle have remained elusive until recently (Johnson and Preuss, 2002;Higashiyama et al, 2003;McCormick and Yang, 2005).…”