User:Mamilln1/sandbox

Article Evaluation
The article on Arabidopsis is relevant to the topic. It offers a general background and some areas goes into more detail about research. I was not distracted by the formal nor the writing.The article is neutral and objective. Some frames such as research are more detailed but understandably so and there is no noticeable bias. No viewpoints are unequally represented, just some subtopics are more represented. Citation links work and direct me to the sources well. The sources do support points made in the article. The information about plant-pathogen resistance links to an article about salicylic acid in plants.The sources are reliable and come form established articles or informational educational or html pages. None are from blogs or biased sources. It is updated recently and information is updated to recent research and new discoveries and new facts are recognized with people and dates. Someone linked an interesting topic--about non-mendelian inheritance that skips generations and shared the info with others so they can read and write up on it. It is part of the Wiki plant project and is rated "B-Class, High Importance." It discusses the phylogeny but it goes into more detail about it. The structure and function of the specific plant are included and why it is important to current research.

Possible Topics
Topics:

1. Pollen tube
This page has very little information of the evolution and mechanism of the tube formation. This is an important structure in transferring pollen, specifically for non-motile sperm, but the article fails to highlight the history of the pollen tube. It also focuses mainly on angiosperms and that too is very simple. There is very little scientific information in regards to newer studies--it only hints at work on cell physiology and internal cues and lacks evidence. It needs to be updated with new knowledge as the basic knowledge and it needs to be connected to the larger focus of pollination and plant reproduction. The talk page has little discussion and one person said that the article seems like a k-12 level one. I could even add this information to the Pollen page because it is ranked as high importance.

I could focus on studies that reflect on cell communication and signaling in pollen tube formation, the evolution of pollen tube from seed ferns to gymnosperms, and highlight the process among different species (specifically in rate of growth).

2. Ginkgo
This page is incomplete and has little information on the structure and contains no images of the gingko tree, aside from the fossil image. There is decent information on the history and environment, however none on the modern ginkgos. Reading the talk page lead me to another article--under Ginkgo biloba which has more in-depth information. This new page has information of about the structure, environment and structure. It is still missing information on some distinct appearance information and importances of the plant with respect to being a gymnosperm.

I could add information about related gymnosperms and features it shares. It is an endangered species, so I could also explore that route and research why it is endangered because they don't talk about the conservation attempts.

3. Gymnosperm
This topic is rated as high importance, yet the article was C-class quality. It lacks information on the phyla of gymnosperms, and does a mediocre job of explaining in the diversity section. However, it does a great job explaining the life cycle in general, but it could be better organized. It also categorizes the all subclasses well and links each one to its own page. The uses could be expanded upon as the wood and fragrances are of great importances. Overall, the article does not capture the true variation and diversity among the gymnosperms.

I could contribute information on the different phyla and add relevant information using a recently constructed phylogeny. The page has been updated recently, but the information is not up to date. It could use new information and more description in each section.

[Possible Sources for pollen tube article]
Signaling for pollen tube growth 

-peptide and Ca+2 signaling

-pathway of how female tissues signal

Evolution and growth rate 

-talks about growth rate correlation with fitness

-shows gap in knowledge about competition during pollen tube growth and variation that exist in rate of growth

Other sources to explore

Pollen viability

gametophyte interaction

pollen tube guidance

locus and mechanisms

molecular guidance

interspecific pollen

evolution of pollen tube in gymnosperms from textbook

Outline
I. Pollen tube importance  '''II. Pollen tube Initiation'''
 * pollen tube is necessary for sexual reproduction in plants
 * single celled pollen has vegetative cell in pollen gives rise to pollen tube and generative cell gives rise to 2 sperm cells communication with compatible pollen tube occurs
 * Initiation: lot of pollen compete for 1 egg- faster growing pollen tube
 * variation exists and not fixed for fast growth
 * not all grow at same time
 * gene expression of gametophyte or sporophyte---pollen expresses own enzyme
 * damaged pollen (X/gamma rays) can survive and fertilize
 * Steps include binding, recognition, hydration, germination, growth
 * when multiple ovules- pistal guides pollen to ovules that will receive the sperm

'''III. Pollen tube guidance'''
 * Megasporophyte plays a role
 * style environment provides nutrients (in the peach)
 * prevent selfing in self-incompatible species---increases genetic diversity
 * polypeptides guide pollen tube to ovule
 * Growth
 * only tip elongates to transfer sperm, so cytoskeleton elongates
 * golgi, organelles and vesicles help tube grow
 * Ca plays role
 * Recognition
 * locus recognition at gene level
 * extracellular enzymes can abort the growth
 * Parts in the ovary are participating
 * the synergids adjacent to the egg cell secrete molecules to attract tube
 * cytoplasmic miRNA help direct
 * terminate signal to stop attraction
 * grow along chemical gradient expressed in style or markers on cells

'''IV. Evolution '''
 * Pollen gene expression
 * make own mRNA after anthesis so expresses own genes
 * Pollen tube length and rate
 * vary by species and the pollen
 * pollen from cross vs self shows if species is self-compatible
 * pistal-pollen interaction determines interspecific hybridization.
 * Gymnosperms show transitional features
 * Ginkgo/Cycad have motile sperm that burst and swim to egg
 * Cycads and ginkgo have haustorial pollen tube: grow filaments by soaking nutrients in nucellus and does not penetrate archegonium. It burst in vicinity of the archegonia and releases 2 sperm that has multi flagella to help it swim to egg.


 * Pine/Gnethophyta have nonmotile sperm that grow tube directly to egg
 * Pine have non motile sperm and use pollen tube to grow through archegonium. Discharges cytoplasm of sperm to egg and one unites and the other degenerates.
 * Gnethophyta have pollen tube reaches egg and double fertilization can occur in which bi-nucleated sperm reach undifferentiated female nucleus and 2nd embryo aborts not form endosperm (3n)


 * Angiosperm pollen tubes grow very fast and long distances
 * Non motile sperm in angiosperm grow pollen tube fast
 * Double fertilization must occur for zygote and endosperm
 * Longer style so needs more communicate and intricate pollen tube
 * Egg is well protected
 * Fusion of stigma- fertilize a lot= polyambry

Pollen tube mechanism
Pollen tube formation is important for sexual reproduction to occur in seed plants. Plants have separate structures such as microsporocytes and megasporocytes and the pollen grains are transported to the female gametophyte through wind, water or pollinators. The last step before fertilization is the growth of the pollen tube to transfer non-motile sperm to the protected egg. Pollen tubes are unique to plants and their structure had evolved over plant history. The pollen tube formation is complex and the mechanism is not fully understood, but is of great interest to scientists.

Initiation
Pollen tube growth begins from when the pollen attaches to the stigma. It is followed by recognition and hydration of the pollen that allows for germination of the tube and ultimate growth. In the pollen grain, the generative cell gives rise to the sperm, whereas the vegetative cells have a tube cell that grows the pollen tube. There is competition in this step as many pollen grains may compete to reach the egg. The stigma plays a role in guiding the sperm to a receptive ovule, in the case of many ovules. Only compatible pollen grains are allowed to grow as determined by signaling with the stigma. Some plants have mechanisms in place to prevent selfing such as stigma and anther mature at different times or are different lengths, which significantly contributes to increasing genetic diversity of the next generation.

There is great variation in the rate of growth of pollen tubes and many studies have focused on signaling. The gene expression in the pollen grain has been identified as that of the gametophyte and not of the parental sporophyte, as it expresses its own unique mRNA and own enzymes. In the peach plant, the style environment in which the pollen tube grows through, provides nutrition for the tube's growth to the egg. Pollen tubes are tolerant and even pollen damaged by X-rays and gamma rays can still grow pollen tubes.

Recognition
The female sporophyte must recognize the pollen stuck to the stigma. Often, only pollen of the same species can successfully grow and outcrossed pollen is more successful in growing. With self-incompatibility systems, outcrossed pollen grows and outcompetes self pollen. This is a gene level regulation in which gene loci of the gynoecium allow either self pollen to slowly grow, stop growing or burst while faster growth of outcrossed pollen occurs, increasing genetic diversity. The main component is that this step determines which pollen grains are compatible to grow and parts of the style, and female embryo contribute in determining. Using hybrid species and crossing pollen, the interaction with the style and pollen was found to influence growth of the pollen tube based on compatibility.

Growth and Guidance
The interaction between the stigma-style and the pollen grain is a vital piece that contributes to the growth. The elongation of the tube is achieved with elongation of the cytoskeleton and it extends from the tip, which is regulated by high levels of calcium in the cytosol. The calcium levels help the synaptic vesicles in the membranes grow and extend at the tip. Polypeptides found in the style also regulate growth of tube and specific peptides that play a role in signaling for growth have been identified.

The LURE peptides that are secreted from the synergids, which occupy the space adjacent to the egg cell, can use attractants. Mutant Arabidopsis plant embryos were used and specifically in those without the synergids, the pollen tubes were unable to grow. The growth was also toward embryos of the same species as the pollen, so the intraspecific signaling helps fertilize egg and sperm of the same species. The signaling in the style is important as pollen tubes can grow without the presence of an embryo sac with just interaction with the style. Other parts in the ovary include cytoplasmic factors like miRNA and chemical gradients that attract the tube to grow toward the synergids.

Calcium and ethylene in Arabidopsis thaliana were involved in termination of the pollen tube when it grows near the ovary. The increase in calcium allowed release of the two sperm cells from the tube as well as degeneration of a synergid cell. The chemical gradient of calcium can also contribute to termination early on in tube growth or at the appropriate time.

The length of the pollen tube varies by species and it grows in an oscillating fashion until it is ready to release the sperm near the egg for fertilization to take place. Some fast growing pollen tubes have been observed in lily, tobacco, and Impatiens sultanii. The rate of growth confers advantage to the organism but it is not clear whether the variation in growth rate exists in the population or it has been selected for over generations due to increased fitness.

Evolution
Many transitional features have been identified that show correlation between the evolution of the pollen tube with that of a non-motile sperm. Early seed plants like ferns have spores and motile sperm that swim in a water medium, called zooidogamy. The angiosperm pollen tube is simple, unbranched, and fast growing, however this is not the case for ancestral plants.

In gymnosperms like Gingko biloba and cycadophyta, a haustorial pollen tube forms. The tube simply soaks up nutrients from the female nucellus and grows in two stages.The pollen tube is highly branched and grows on the female sporophyte tissues. First, it grows the main tube followed by a more spherical tip at the end to allow the sperm to burst near the archegonia. The binucleated, multiflagellated sperm can then swim to the egg. Cycads have a less branched structured and the tip end swells the same way as in the gingko. In cycads, however, various enzymes have been identified in the pollen tube that direct growth and the nucellus tissues are more damaged with the tube growth.

In other phyla of gymnosperms, coniferophyta and gnethophyta, the sperm is non motile, called siphonogamy and the pollen tube grows through the archegonia to help the sperm reach the egg more directly. Conifers can be branched or unbranched and they cause degeneration of the female tissue as it grows through more tissue. Pines, for instance discharge cytoplasm of the sperm and union of the one sperm occurs as the other sperm degenerates. Yet, in gnethophyta, there are features more similar to angiosperm pollen tubes where the tube reaches the egg with a early form of double fertilization. However, the endosperm does not form and the second fertilization is aborted.

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. There is great variation in pollen tubes in angiosperms and many model plants like petunia, Arabidopsis, lily and tobacco plants have been studied for intraspecific variation and signaling mechanisms. In flowering plants, a phenomenon called polyambry 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.