Week 9 notes
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This 6 page Class Notes was uploaded by Casey Notetaker on Friday February 19, 2016. The Class Notes belongs to BIOL 3040 at Clemson University taught by Christina Wells in Spring 2016. Since its upload, it has received 17 views. For similar materials see Biology of Plants in Biology at Clemson University.
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Date Created: 02/19/16
Week 9: Chapter 22 1. Two Phases of Seed Development a. Embryogenesis i. Establishes the basic body plan ii. Apical-basal patterning along main axis 1. Apical cell will become embryo 2. Basal cell will become suspensor iii. Radial pattern of concentric tissue layers iv. ** First mitotic division of the zygote is asymmetrical and transverse b. Maturation: build up of food reserves, followed by desiccation and hardening of integuments i. Endosperm is gone—food reserves are in specialized storage cotyledons ii. Rest of embryonic leaves are in the form of a plumule (short stem or epicotyl with attached leaves) iii. Apical meristem is down in between the foliage leaves iv. ** Build up of final food reserves in endosperm of cotyledons v. Desiccation (about 90% water loss) vi. Seed coat hardens vii. Seed becomes quiescent or dormant 1. Quiescent: seed is capable of germinating right away; resting; but capable of germinating given sufficient water and favorable conditions 2. Dormant: incapable of germinating given sufficient water and favorable conditions; some other condition(s) must be met before germination is possible 2. Dormancy: condition of being unable to germinate, even when environmental conditions are favorable a. Both seed coat and embryo can cause dormancy—many mechanisms b. Dormancy ensures that seed will only germinate when it receives specific environmental cues c. Dormancy- breaking mechanisms i. Sustained low temperatures ii. Mechanical damages to seed coat iii. Sustained rainfall washes away inhibitors in seed coat (desert plants) iv. Light required (ex- early successional trees) 3. Imbibing a. Seed takes up water b. Enzymes in the seed are activated and new enzymes are synthesized begin breaking down stored food c. Seed swells, develops pressure, ruptures seed coat d. Aerobic respiration can take place when seed coat is broken e. Embryo cells begin to divide and grow again 1. Germinating a. Parts of the mature embryo/germinating seedling: i. Radicle: first root to emerge from seed ii. Cotyledon: seed leaf; may look diff than later foliage leaves iii. Hypocotyl: area between radicle and cotyledon attachment point iv. Epicotyl: area above cotyledon attachment point and below next set of leaves v. Plumule: portion of the seedling above the cotyledons b. Epigeous: hypocotyl is elongated and bent- this “hook” pushes up throught the soil, pulling the cotyledons with it; portion of embryo between cotyledons and first true leaves i. Cotyledons above ground; seedling gets to use cotyledons for photosynthesis ii. Example= common bean iii. Stored food in cotyledons is digested and sent to rest of plant – in endosperm 1. Cotyledons digest the stored food reserves of the endosperm, transferring them to the rest of the plant iv. Cotyledons may photosynthesize briefly, but will eventually whither and fall off c. Hypogeous: the epicotyl rather than the hypotcotyl that forms the hook; portion of embryo between cotyledons and root i. Cotyledons remain underground; protects cotyledons from predation; can be heavy and hard to pull out of ground ii. Example= acorns/oaks iii. Stored food in cotyledons is digested and sent to rest of plant d. Germinating in the onion (monocot) i. Single tubular cotyledon forms the hook* ii. e. Germinating in corn (monocot) i. Cotyledon (scutellum) never leaves the seed ii. Stored food in endosperm is digested by cotyledon iii. Coleorhizae and coleoptile emerge first iv. Radicle emerges from coleorhizae v. First leaves emerge from opening at coleopticle vi. vii. Radicle: First root to emerge from seed; at its tip is root apical meristem viii. Coleorhiza: sheath enclosing the radicle ** ix. Cotyledon= scutellum (single cotyledon of a grass embryo, specialized to digest and absorb the endosperm x. Plumule: shoot apical meristem and first foliage leaves xi. Coleoptile: sheath enclosing the plumule** xii. Aleurone: outermost, protein-containing layer of endosperm** 1. Asexual Reproduction a. Vegetative (asexual) reproduction i. Suckers: are root sprouts that can give rise to new plants ii. Layering: occurs when a branch touches the ground and roots while still attached to the parent plant; may eventually detach and become independent; mainly happens in woody plants iii. Stolons/runners: are stems that grow at (or just below) the soil surface, forming adventitious roots at the nodes and sending up new shoots from the buds iv. Rhizomes: are stems that grow horizontally below the soil surface; each node can give rise to a new plant; may be fleshy and enlarged to serve as a storage organ v. “Natural cuttings”: are produced by plants like willow that grow on the edge of a creek; these are small, viable, branches that are shed, swept downstream and eventually root to form new trees vi. Reproductive leaves: found in a small number of plant species vii. Apomixis: production of embryos asexually form the parent plant; meiosis is bypassed and fertilization doesn’t take place; resulting seeds are genetically identical to the parent plant 1. Examples: some citrus orchids, grasses 2. Advantages: a. Assured reproduction in the absence of pollinators, such as in extreme environments b. Maternal energy not wasted in unfit offspring (cost of meiosis) c. Some apomictic plants (but not all) avoid the male energy cost of producing pollen 3. Disadvantages: a. Can’t control accumulation of deleterious genetic mutations b. Usually restricted to narrow ecological niches c. Lack ability to adapt to changing environments 2. Meristems and Primary Tissues a. Embryogensis is only the beginning of plant development b. Subsequent development occurs the activity of meristems, populations of cells that retain the ability to divide after embryogenesis is complete c. *** Most plant development takes place after embryogenesis and germination through the activity of meristems i. Meristems: region of undifferentiated, dividing cells ii. Apical meristems: found at root and shoot tips; give rise to primary tissues 1. Initials: divide and maintain the meristem as a continuous source of new cells 2. Derivatives: become new body cells a. May divide a few more times before undergoing differentiation b. Give rise to the three “primary meristems”—partly differentiated tissues that remain meristematic for some time before differentiating into specific cell types c. Protoderm, procambium, ground meristem d. Apical meristem protodermdermal tissues (epidermis) e. Apical meristem ground meristem ground tissues (parenchyma, collenchyma, sclerenchyma) f. Apical meristemprocambium vascular tissues (primary xylem and phloem) iii. Lateral meristems (cambia): cylindrical vascular and cork cambia; give rise to secondary tissue
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