Pollen tube
Once a pollen grain settles on a compatible pistil, it may germinate in response to a sugary fluid secreted by the mature stigma.
The germinated pollen tube must drill its way through the nutrient-rich style and curl to the bottom of the ovary to reach an ovule.
Some plants have mechanisms in place to prevent self pollination, such as having stigma and anther mature at different times or being of different lengths, which significantly contributes to increasing genetic diversity of the next generation.
In mutant Arabidopsis plant embryos, specifically in those without the synergids, the pollen tubes were unable to grow[citation needed].
[9][5] Other parts in the ovary include cytoplasmic factors like miRNA and chemical gradients that attract the pollen tube to grow toward the synergids.
[13] Early seed plants like ferns have spores and motile sperm that swim in a water medium, called zooidogamy.
[13] In angiosperms, the mechanism has been studied more extensively as pollen tubes in flowering plants grow very fast through long styles to reach the well-protected egg.
[12] In flowering plants, a phenomenon called polyamory can occur where many ovules are fertilized and overall fitness of the organism is yet to be studied with respect to rate of pollen tube growth.
[19] They are easily cultivated in vitro and have a very dynamic cytoskeleton that polymerizes at very high rates, providing the pollen tube with interesting mechanical properties.
The internal machinery and the external interactions that govern the dynamics of pollen tube growth are far from being fully understood.
[21] Each unique arrangement, or pattern, contributes to the maintenance of polarized cell growth characteristic of the pollen tube.
In order to experimentally observe distributional changes that take place in the actin cytoskeleton during pollen tube growth, green fluorescent proteins (GFPs) have been put to use.
[21] GFPs were mainly selected for the purposes of dynamic visualization due to the fact that they provided an efficient means for the non-invasive imaging of actin filaments in plants.
[23] Lifeact-mEGFP has been used as a marker to study the dynamics of actin filaments in the growing pollen tubes of tobacco, lilies and Arabidopsis.
[23] Through studies conducted with GFP, it has been confirmed that the dynamic state of actin filaments located in the apical region are essential for pollen tube growth.
These findings have provided evidence supporting the theory that actin filaments located in the apical region are highly dynamic and are the site of vesicle targeting and fusing events.
Genetic knockouts of AtFH5 resulted in a decreased abundance of actin filaments in both apical and subapical regions of the pollen tube, thereby providing more evidence to support the theory that AtFH5 nucleates actin filament assembly in apical and subapical regions of the pollen tube.
[25] Extensive work has been dedicated to comprehend how the pollen tube responds to extracellular guidance signals to achieve fertilization.
The actin filaments in the cytoskeleton, the peculiar cell wall, secretory vesicle dynamics, and the flux of ions, to name a few, are some of the fundamental features readily identified as crucial, but whose role has not yet been completely elucidated.
During pollen tube growth, DNA damages that arise need to be repaired in order for the male genomic information to be transmitted intact to the next generation.
[32] In order for fertilization to occur, there is rapid tip growth in pollen tubes which delivers the male gametes into the ovules.
[37] The F-actin controls the accumulation of the homogalacturonans full vesicles- essentially mediating tip growth- in the subapex region.
[38] The actin filaments controls the apical membrane and cytoplasm interactions while the pollen tube is growing in the apex region.
[39] The F-actin from the apical membrane makes an actin binding protein called formin which is essential for pollen tube tip growth.
These two methods demonstrated that there was an abundant presence of the RMD transcripts in the lemma, pistil, anther, and mature pollen grains.
[42] Histochemical staining of the tissues of these transgenic plants then showed high GUS activity within the pistil, anther wall, and mature pollen grains.
Detection of GUS signals were employed once again in order to study where RMD is specifically expressed within the pollen tube.
Therefore, these combined results demonstrate that the PTEN-like domain is responsible for the tip localization of RMD in the pollen tubes.
Fluorescent intensity was measured using statistical analysis in order to observe the actin filament densities within the pollen tubes.
Therefore, these combined results support that the proper organization of actin cables as well as normal F-actin densities within the tip of the tube can only be achieved if RMD is present.
