Cooksonia pertoni with sporangia Shrewsbury, England Upper Silurian Size of the plant 2.5 cm Cooksonia pertoni South Wales

Homework!!!! Your Plant Evolution Lab is due tomorrow! Do Not Waste your time!!!

Do IT NOW!!!! 1.When two gametes unite, they form a ____________. 2.After meiosis, a diploid cell produces __________ cells. 3.If haploid cells undergo mitosis, what type of cells are formed? 4.What does a gametophyte produce? 5.What does a sporophyte produce?

Charophyta – green algae Green algae in the group Charophyta are commonly known as charophytes. They include many freshwater and terrestrial green algae. Chara and other stoneworts are among the largest and most structurally complex of the charophytes. Their main branches have whorls of short lateral branchlets at intervals. They usually grow submerged in mainly still, fresh or slightly brackish waters.

Chlorphyta and charophyta

Chlamydomonas will “mate” When gametes of opposite mating types are mixed, their flagella immediately agglutinate. This initial recognition event (Stage 1 in the diagram below), which is both gamete and mating type specific, is followed by one or more signals. These signal(s) trigger a series of events (Stage 2): (a) the cells release autolysin, an enzyme which digests the cell walls, (b) the flagella, which initially show a loose interaction along their entire length, now demonstrate tipping, a tighter interaction that occurs only at the flagellar tips, and (c) the mating structures, located on the cell (plasma) membrane, in close proximity to the flagellar origin, become "activated". Activation of cells of mating type + (mt+) results in production of a long, membrane-enclosed mating tubule (the activated mating structure) covered with a glycoprotein "fringe", and containing polymerized actin filaments. This activated mating structure is analogous to the acrosome found on sperm (the first sperm component to react with the egg). The mt- cells respond by moving membrane proteins (particles) to the center of the mating structure, a region of the plasma membrane that had been cleared of particles during gametogenesis, and producing a short- lived tubule with no microfilaments. When the two activated mating structures come into contact, they appear to be held together by an adhesive interaction (Stage 3), finally leading to fusion between opposite mating type cells (Stage 4) Stages in the mating reaction Mating-Defective Mutants A sex-limited mutant is expressed in only one mating type. Cells of the other mating type may carry the gene but do not express it, presumably because the gene is for a function specific to only one mating type. See the description of the fusion-defective mutants on the next page, or click the phase contrast image of the mutants below. Phase contrast image of adhering mutants These mutants are adhering by their mating structures Comparison with other organisms It is interesting to note the similarity between the fine-structural aspects of the mating process in this organism and the sperm-egg interaction of invertebrates and mammals. These contact-initiated events in invertebrates and Chlamydomonas lead to the production of long, microfilament-filled projections (the fertilization tubule of mt+, and the acrosomal process of the sperm). Following the acrosome reaction, the acrosomal process is covered with an adhesive material called bindin, which adheres to a glycoprotein receptor found in the vitelline layer of the egg. This adhesion between gametes is believed to be essential for subsequent gamete fusion and it has been suggested that bindin might act as a fusogen. In Chlamydomonas, the mating structures also appear to be covered with a glycoprotein that is involved in the adhesion of these gametes. Mammalian sperm have been shown to adhere and fuse with actin-filled projections (microvilli) found on the egg plasma membrane. We hope to obtain a better understanding of the biochemistry of the adhesion and fusion of gametes of Chlamydomonas, an organism which may resemble the primitive ancestor of all plants. It is also possible that a similar, non-photosynthetic organism gave rise to animals. Chlamydomonas seems to have retained its primitive state and allows one to begin to understand some of the events involved in fertilization in an organism amenable to genetic analysis. The molecular basis of fertilization in organisms other than sea urchin is not well understood and isolation and analysis of a fusion protein in Chlamydomonas may prove very helpful in understanding the mechanisms of fertilization.

Plants move from water to land and encounter some unique problems that direct their evolution Desiccation Solar radiation Dispersal Fertilization

moss life cycle animation

Sporopollenin Pollen and spores are protected by this compound whose chemical make up is not entirely known

fern animaiton

Gymnosperms life cycle life cycle

Flowering Plants – Double Fertilization Microspore = pollen

Seeds in a Pod, Arabidopsis sp. (SEM x220). This image is copyright Dennis Kunkel at used with permission.

Flowering Plants!!!! Double Fertilization animation