PLSC Lab Seven

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PLSC Lab Seven
2013-04-01 21:41:26
Lab Seven

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  1. Gametyophyte
    Any haploid plant structure
  2. Sporophyte
    Any diploid plant structure
  3. Alternation of generations
    The cycle from gametophyte to sporophyte
  4. Seed coats
    Protect the contents of a seed by restricting the contents of a seed by restricting water and gas exchange, or infection by bacteria and fungi.
  5. Hilum (dicot)
    A scar found externally on the dicot seed, an indentation or scar that can be seen on one side. It is where the seed was attached tot he ovary wall in the fruit.
  6. Microphyle (dicot)
    Just below the hilum, this is a pore. During fertilization, the pollen tube enters the ovary through this opening
  7. Embryo (dicot)
    • One is contained within the seed and can remain alive for many weeks or even years. The are in contact with the seed coat to ensure better access for gas exchange.
    • Every embryo has plumule, which is the embryonic leaf, a radicle from which the root system will develop, and epicotyl from which the shoot system will develop, and a hypocotyl representing a middle region between the radicle and the seed leaves known as cotyledons. Because it is often difficult to distinguish between the hypocotyl and the radicle in the embryonic stage, this region is also known as the hypocotyl-radicle axis
  8. Embryo of grasses
    Tend to be linear in shape. The single cotyledon is called the scutellum and is shield-like in shape.  The embryo is found rest on top of the scutellum and is composed of a plumule which is enclosed in a flap of tissue called the coleoptile. It protects the leaf as it is being pushed through the soil.  Likewise, the root is protected by a flap of tissue called the coleorhiza.
  9. Gymnosperm seeds
    contain an energy-rich mass of food for the embryo, called the megagametophyte. Haploid cells associated with the megasporangium undergo multiple mitotic cell division after fertilization of the egg to produce this energy source for the embryo.  When the seed coat breaks open, the radicle give rise to a primary root and the cotyledons begin absorbing energy directly from the megagmetophyte. As the hypocotyl and cotyledons begin to grow, the megagametophyte and seed coat are forced up out of the soil. Eventually the cotyledons shed the megagametophyte, after which new leaves will develop form the epicotyl
  10. Angiosperm seeds
    Also contain energy-rich mass of food called the endosperm. In addition, angiosperms have an unusual system of fertilization, wherein one sperm fertilizes the egg and another sperm fuses with 2 haploid nuclei called polar nuclei, which then develops into endosperm.  This double fertilization produces  diploid embryo and troploid endosperm.  Angiosperms also differ from gymnosperms by possessing a predictable # of cotyledons in the embryo.
  11. Dicot embryos
    • Absorb endosperm energy in one of two ways.  In on case, the hypocotyl is directly connected to a pair of enlarged cotyledons that absorbed all the endosperm, or cover a large surface area of the endosperm.  The radicle is the first thing to develop once the seed coat splits.  In come cases, the hypocotyl begins to elongate and grow up towards the surface.  The hypocotyl bends, and pulls the cotyledons and/or endosperm above ground. Pulling protects the shoot tip from damage that would otherwise occur if it pushed up through the soil.  The enlarged cotyledons can immediately begin photosynthesizing, but eventually wither and fall off once several true leaves have developed.  This form of seedling emergence is called epigeal or epigeous (above ground)
    • In another case, the epicotyl elongates and emerges above ground, forming an arch to pull the delicate shoot tip out of the soil.  However, the cotyledons remain below ground, providing energy until the first true leaves are produced on the young shoot.  The form of seedling emergence is called hypogeal or hypogeous (below ground)
  12. Monocot embryos
    Absorb endosperm energy through a single cotyledon, known as the scutellum.  The radicle is enclosed within a coleorhiza at one end of the embryo, an the epicotyl and first leaves or plumule are enclosed within a coleoptile at the other end. These structures serve to protect the delicate developing root and shoot.  When the seed coat splits, the radicle forms a primary or seminal root that penetrates through the coleorhiza.  The coleoptile grows up above the soil surface, and this splits to allow the first true leaves to emerge.  The endosperm remains in the seed coat and below the ground to fuel this early development, until the first true leaf begins photosynthesis and energy production.  In other monocots, a hooked cotyledon emerges above ground with the endosperm and seed coat still attached (onion or lily).  This is superficially similar to gymnosperms, and to one kind of dicotyledonous emergence.
  13. Germination
    Is the growth and development stage between a mature embryo and emergence of the seedling.
  14. Imbibition
    The first step in germination, and involves rehydration of the seed with water absorbed from the soil, or surrounding environment.  Imbibed seeds often swell and increase in both size and weight
  15. Seed viability
    Common term used to describe whether the embryo within the seed is still alive. Viability can be determined on imbibed seeds and chemical dyes to observe if the embryo is respiring, and is often expressed as a percentage
  16. Percentage germination
    The percentage of seeds that germinate under certain conditions in a testing laboratory is not the same as viability.
  17. Dormant
    Some species of mature and viable seeds will remain dormant until prolonged exposure to cold and/or hot temperatures (stratification) under dehydrated or imbibed conditions or physical or chemical alteration of the seed coat (scarification) breaks dormancy and permits germination.
  18. Seed purity
    indicates the proportion of the seed lot contents that are of the desired species
  19. Pure Live seed (PLS) %
    =purity x [germinability or viability]
  20. Monocarpic (one fruit) or semelparous (same time birth)
    After emergence, some plants reproduce once, then die
  21. Annual plants
    Monocarpic or semelparous, will germinate from seed, develop, reproduce and die within 12 months.
  22. Biennial plants
    Monocarpic or semelparous, will develop vegetatively in the first year, then reproduce and die in the second year. All annuls and biennials are herbaceous and commonly inhibit chronically disturbed or unpredictably moist environments
  23. Polycarpic (many fruit) or iteroparous (again birth)
    • Plants that grow and reproduce many times in their life.
    • Perennial is the encompassing term for plants that live more than two years, and normally polycarps fall into this group.  All woody plants and many herbaceous dicots are perennial. These tend to have short-lived seeds
  24. Phenology
    Is the timing of biological events in relation to the annual cycle of environmental events.
  25. Staging
    Is a formal means of identifying the level of development of a particular crop.
  26. Natural source-sink patterns
    If you know something about these patterns of carbohydrate allocation between leaves and roots, it is possible to intelligently plan optimum timing for defoliation, with little impact on root storage