Week 3+4 Notes
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This 11 page Class Notes was uploaded by Nausheen Zaman on Monday February 8, 2016. The Class Notes belongs to BIO1500 at Wayne State University taught by Dr. William Bradford in Winter 2016. Since its upload, it has received 142 views. For similar materials see Basic Life Diversity in Biology at Wayne State University.
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Date Created: 02/08/16
*Note: Please DO NOT return after purchase. Thank you!* Chapter 31: Seed Plants ● Evolution of Seed Plants ○ First appeared 300 MYA *million years ago* ■ Evolved from progymnosperms (sporebearing plants) ■ Large # ogene duplicationsa level of molecular evolution where new genetic material is created from existing whole genome duplicatio (when an entire genome is revamped to consist of entirely new genes from the original species) ○ ~319 MYA → seed plants evolved ○ ~192 MYA → Angiosperms (flowering plants) appeared ○ Success attributed to seed evolution, the seed: ■ Protects/provides nourishment for enclosed embryo ■ Allows germination to pause for periods of harsh weather before germinating ■ Later develop into fruit for enhanced dispersal ● Gene duplications = new gene functions ○ Duplicate gene = a backup gene that can mutate without being lethal to the organism ○ Different types of divergence: ■ Subfunctionalizati where a gene is split into two separate genes with different traits ■ Neofunctionalizati where a gene is completely revamped using traits expressed in the old gene ■ Degeneration/Gene loss where a gene is completely gone/replaced ● Seed = embryo protection and nourishment ○ Embryo protected byintegument (extra sporophyte tissue layer that hardens into seed coat) ● Water not needed for sexual reproduction ○ Male gametophytes ■ Pollen grains (sperm) ■ Dispersed by the wind (pollinator) ■ No need for water ollen tub(a tube from the pollen grain that deposits the sperm into the egg once it is on a stigma of a flower) ○ Female gametophytes ■ Develop within ovule(part of the ovary containing an unfertilized egg) ■ Enclosed within diploid sporophyte tissues (angiosperms) ● Ovary ovule + surrounding protective tissues → later develop into fruit Why is water not essential for fertilization in seed The male gametophyte evolved to make pollen grains and other mechanisms to aid their reproduction when water isn’t around. *REFER TO PLANT TABLE!!!!* *Note: Please DO NOT return after purchase. Thank you!* ● Gymnosperms (‘naked seeds’) ○ Lack flowers + fruits ○ Have ovule → seed that is exposed ocal(modified shoot/leaf) ○ Conifers (Coniferophyta) ■ Most familiar gymnosperm phylum (pines, spruces, firs, etc.) ● Coastal redwood tallest living vascular plant ● Bristlecone pine oldest living tree ■ Found in colder temperatures and drier regions ■ Source of important products ● Timber, paper, restaxol(compound that inhibits cancerous growths) ■ Pines ● >100 species (all in Northern hemisphere) ● Produces tough needlelike leaves in clusters ○ Thick cuticles + recessed stomata = decreased water loss ○ Also secrete resin through canals to deter insect + fungal attacks ● Thick bark = survives fires and subzero temperatures ■ Pine Reproduction ● Male gametophytes = pollen grains (fmicrospores(smaller male spores) in male cones via meiosis) ○ Male cones… ■ Develop in clusters of 3070 ■ Typically at lower branch tips ■ 14 cm long ■ Small, papery scales arranged in spirals/whorls ○ Pair o microsporangia(sporangia containing microspores) form as sacs within each scale ○ Microspore mother cellsdiploid cells that form microspores) in microsporangia go through meiosis ■ Mother cell → four microspores → fourcelled pollen grain with air sacs for buoyancy ● Female pine cones form on upper branches of the same tree ○ Larger with woody scales ○ Two ovules on each scale containing a megasporangium calleducellus (central part of ovule with the embryo sac) ■ Nucellus surrounded by integument icropyle (a small opening on the ovule that allows pollen tube to penetrate and deposit sperm cells to the egg) on each end ○ Megaspore mother cell (diploid cells that form megaspores) within each megasporangium (sporangia only containing megaspores) reproduces via meiosis *Note: Please DO NOT return after purchase. Thank you!* ■ Becomes a row of four megaspores → three break down → remaining one = female gametophyte ○ Mature female gametophyte consists of thousands of cells, with 26 archegonia formed at the micropylar end ■ Each archegonium = single egg ● Female cones usually take 2 or more season to mature ○ First spring female cone scales spread apart for pollen to drift in between open scales ■ Some grains get stuck in sticky fluid from micropyle → drawn down through micropyle to top of nucellus → scales close ● Female gametophyte not mature for a year ○ Meanwhile… ■ Pollen tube emerges from pollen grain ■ Tube digests from nucellus → archegonia ○ During pollen tube growth… ■ One of the four cells of the pollen grain, the generative cell(the cell that gives rise to sperm cells) undergoes mitosis → two identical cells → one cell → two sperm cells ○ 15 months later… ■ Pollen tube finally reaches archegonia and deposits sperm ■ One sperm + egg = zygote → embryo with seed ● Other sperm + pollen cells degenerate ■ After dispersal and germination of seed, next gen. sporophyte grows into a tree ○ Cycads (Cycadophyta) ■ Slow growing gymnosperms from tropical/subtropical places ■ Resemble palm trees ■ Life cycle similar to pine ● Female cone = 45kg! ■ Have largest sperm cells of all organisms ○ Gnetophytes (Gnetophyta) ■ Only gymnosperm with vessels in xylem ■ Three (unusual) genera ● Gnetum ● Welwitschia ● Ephedra ○ Meth and ephedrine produced from these plants! ○ Ginkgophytes (Ginkgophyta) ■ Only one living species remains (Gingko biloba) ■ Flagellated sperm) *Note: Please DO NOT return after purchase. Thank you!* ■ Dioecious(male/female on different trees) ● Angiosperms (flowering plants) ○ Highly specialized and recently evolved ○ Highly diversified (>300K species) with various structures and pollinators ○ Ovules enclosed in diploid tissue during pollination ○ Carpel (modified leaf that covers a seed) → fruit ○ Floral structure ○ Flower whorls ■ Thought to have been evolved from leaves ■ Outemost whorl calyx/sepal(35) ● Leaflike, green ■ Second whorl corolla/petal (35) ● Separate, fused together or missing (windpollinated flowers only) ● Function to attract pollinators ■ Third whorlandroecium/stamens ● Pollen produced here ● Each stamen = pollen bearing panther and a stalfilamen) ○ Filament may be missing in some plants ■ Innermost whorlgynoecium/pistil ● Consists of one/more carpels housing female gametophyte ■ Carpel = Three major regions ● Ovary swollen base containing ovules (later develops into fruit) ● Stigma tip where pollen gets stuck (sticky/feathery) ● Styl neck/stalk leading down to ovary ○ Flowers = gametophyte generation ■ Modified stems bear modified leaves *Note: Please DO NOT return after purchase. Thank you!* ■ Primordium (The rudimentary stage of a plant) → pedicel (a bud developed at the end of a stalk that later turns into a flower) → expands to form receptacle (where other parts are attached) ■ Parts arranged into circhorls) ○ Egg production ■ Megaspore mother cell goes through meiosis → Produces 4 megaspores → 3 disappear → Nucleus of remaining megaspore divides once mitotically → two daughter nuclei divide TWICE → 8 haploid nuclei → integuments become seed coat ■ Polar nuclei One nucleus from fournucleigroup travel towards center ■ Cell walls form around remaining nuclei ■ Group closest to micropyle = one cell (egg) + tw ynergids cells that help the pollen to reach the egg cell) ■ Other group =ntipodals(no real function and break down) ■ Female gametophyte = resulting sac with eight nuclei in seven cells (embryo sac) ● Completely dependent on sporophyte for nutrition, multicellular, haploid ○ Pollen production ■ Occurs in anthers ● Anthers have patches of tissues (comes in fours) that become chambers with nutritive cells inside ● Tissue in each patch = many diploid microspore mother cells that undergo meiosis simultaneously producing four microspores ● Microspore nucleus divides ONCE → four nuclei separate → two layered wall develops around each microspore → walls between adjacent pairs of microspores break down as anther matures ○ Binucleate cells with two nuceli) microspores = pollen grains ○ Pollination & male gametophyte ■ Pollinatio a mechanical transfer of pollen from the anther to the stigma of a flowering plant ■ Takes place between flowers of differing plants ■ Brought about by insects, water, gravity, wind and animals ■ ¼ of all angiosperms pollen grain deposited directly to stigma of its own flower selfpollinati n) ■ May/May not be followed by fertilization ● Depends on genetic compatibility of pollen grain and stigma ■ If stigma receptive → tube cell develops into pollen tube → guided towards embryo sac → grows through style and into micropyle → generative cell develops into two sperm cells from their nucleus (nonflagellated) ○ Double Fertilization *Note: Please DO NOT return after purchase. Thank you!* ■ Pollen tube enter embryo sac → destroys synergid → discharges contents → one sperm + one egg = diploid zygote (new sporophyte) → other sperm + two polar nucelriploid endospermnucleus (a endosperm formed from diploid parents is usually triploid (2m: 1p)) If the endosperm failed to develop in a seed, how would the seed’s fitness be affected? Explain? The fitness of the seed will not exist because the endosperm is an essential for the seed to survive. The endosperm provides nutrients for the seed and it can’t survive without it. ● Seeds ○ Gymno/angiosperms embryonic development arrested after fertilization ○ Integuments → relativeimpermeable (nothing can really pass through) seed coat → Dormant (inactive) embryo enclosed along with stored food → germination occurs with presence of water and oxygen to embryo ○ Important adaptation because… ■ Dormancy under unfavorable conditions ■ Protect the young plant at most vulnerable stage ■ Provides food for embryo ■ Facilitation of embryo’s dispersal ○ Serotiny adaptations that ensure embryos develop only under certain conditions ○ Pyriscence Seeds that don’t disperse until activated by fire (i.e. jack pine) ○ Some seeds germinate after inhibitory chemicals are leached (drain away naturally) from seed coat (ensures sufficient water availability) ○ Some seeds germinate through animal’s digestive systems (weakens seed coat, aiding in dispersal) ● Fruits ○ Protect seeds ○ Defined as mature ovaries ○ During seed formation flower ovary → fruit ■ Fruits can also develop without seed development (commercial bananas) ○ Fruits are adapted for dispersal ■ Pericarp ovary wall ● Exocarp, mesocarp, endocarp (think of the 3 tissue layers of an embryo, except with ‘carp’ at the end because it comes from a ‘carpel’) ■ Fate determines fruit type ■ Contain 3 genotypes in 1 package ● Fruits/seed coat = prior sporophyte gen. ● Developing seed = remnants of gametophyte gen. ● Embryo = next sporophyte gen. ○ Types: ■ True berries ● Fleshy pericarp, thin skin ● Multiple seeds in one/more ovaries *Note: Please DO NOT return after purchase. Thank you!* ● Tomatoes ■ Legumes ● Split two carpel edges ● Seeds attached to edges ● Pericarp dry at maturity ■ Drupes ● Seed enclosed in a hard pit ● Peaches, plums, cherries ● Each pericarp layer is different in structure and function ● Endocarp = pit ■ Samaras ● Not split ● Wing from outer tissues ● Maples, elms ■ Aggregate Fruits ● Many ovaries on a single flower ● Blackberries, strawberries ● Ovaries NOT fused and covered by continuous pericarp ■ Multiple Fruits ● Flowers form fruits around a single stem ● Fruits fuse together ● Pineapple ○ Fruit dispersal = ability for angiosperms to colonize large areas ■ Ingestion/transport of birds/other vertebrates ■ Attaching to outside and catching a ride ■ Blowing in the wind ■ Floating in water Chapter 41: Plant Reproduction ● Reproductive development ○ Angiosperms = evolutionary innovation with flowers/fruits ○ Plants go through developmental changes leading to reproductive maturity by adding meristems (Region of plant tissue full of newly dividing cells ○ Germinating seed → vegetative plant vorphogenesis (biological process that allows organisms to develop their shape via cellular growth/differentiation) ○ *Refer to Slide 16 on Jan29 lecture slides* ○ Once plants are competent for reproduction a combo of factors (light, temperature, water, promotive/inhibitory signals) determine when a flower will be produced ● Phase Change transition to flowering (triggered by internal signals) ○ Can be subtle or obvious ○ Oak trees lower branches (juvenile phase) hold on to their leaves in the fall ○ Juvenile ivy = adventitious (formed accidentally or in an unusual placement) roots *Note: Please DO NOT return after purchase. Thank you!* ● Flower Production ○ Four geneticallyregulated pathways have been identified, plants (usually) depend on one, but all four can be present in a plant ○ Lightdependent pathway (Photoperiodic pathway Based on amount of light/dark in a 24hr cycle ■ Shortday plant = flower when daylight is shorter (cocklebur) ■ Longday plants = flower when daylight is longer (clovers) ■ Day neutral plant= don’t depend on light at all ■ Obligate long/shortday plan= SHARP DISTINCTION between the two ■ Facultative long/shortday pla= VERY LITTLE DISTINCTION between them (flowering occurs quicker/slower based on how much light there is) ■ Light used as a cue for: ● Optimal abiotic conditions ● Available pollinators ● Decreased resource competition ■ Can be manipulated! (Poinsettias) ○ Tempdependent pathway ■ Vernalization when a plant requires a period of cold weather before flowering (i.e. daffodils, tulips) ○ Gibberellindependent pathway ■ Gibberellin a hormone that promotes elongation and flowering ○ Autonomous pathway ■ No environmental cues needed for flowering (some species of tobacco plants) ● Flower types ○ Complete a flower with all four floral parts (sepal, petal, stamen, carpel) ○ Incomplete a flower lacking one or more of the floral parts ○ Perfect ○ Imperfect ● Trends in Floral Evolution *See slide 34 of Jan29 lecture slides for table* ○ 2 major trends ■ Separate floral parts grouped/fused ■ Floral parts lost/reduced ● Modifications usually relate to pollination mechanisms ○ Floral symmetry ■ Primitive = radial (buttercups) ■ Advanced = bilaterally symmetrical (orchids, snapdragons, etc.) ○ Ovary position ■ Varies across species ■ Superior = hypogynous ■ Inferior = epigynous *Note: Please DO NOT return after purchase. Thank you!* ● Pollination when pollen is placed on a stigma ○ Self pollinatiCross pollinatio (when pollen from one flower gets on another flower’s stigma) can occur ○ Successful pollination depends on regular pollinator attraction ○ Floral morphology and pollinators have coevolved (early seed plants wind pollinated) ○ Insect pollinated angiosperms majority of them are pollinated by bees ■ Bees typically visit yellow/blue flowers ■ Flowers may have patterns indicating location of nectaries to bees (bull’s eye is ONLY visible to bees) ■ Nectaries = an area in the throat of specialized flowers that provide a source of food for some adult bees and larvae ■ Most bees collect pollen (provides food for larvae) ■ Few hundred species of social/semisocial bees exist ■ 1000 parasitic (living on other bee’s nests) species ■ Majority are solitary (18K species total) ● Solitary bees = single generation of offspring ● Adults are only active a few weeks out of their whole life ● Often use a particular group of plants as a source of larvae food (coevolution) ○ Phlox landing platforms (for flowers visited regularly by butterflies) ○ Flowers that are white/pale visited by moths (jimsonweed, primrose) ■ Tend to be heavily scented and easier to locate at night ○ Flowers visited by birds lots and lots of nectar (hummingbirds!) ■ Often red in color and inconspicuous to insects ○ Other animals (bats, small rodents) may aid in pollination and dispersal of seeds and fruit ○ Some angiosperms windpollinated ■ Characteristic of early seed plants ■ Flowers small, green, odorless, reduced/absent corollas (groups and hanging down in tassels) ■ Stamen and carpel containing flowers usually separated individuals (increases chances of outcrossing) ○ Dioecy when a plant is both male and female (Chinese treeofheaven) ○ Outcrossing advantageous for eukaryotic organisms and plants and some strategies promote outcrossing… ■ Separation of male and female structures ● Dioecious plants produce only female/male parts ● Monoecious plants produce male/female on the SAME plant ○ Selfpollination is frequent because ■ Ecologically favored under certain circumstances ■ Offspring are more uniform and better adapted to their environments *Note: Please DO NOT return after purchase. Thank you!* ○ Dichogamous when female/male parts are on the same flower but reach maturity at different times ● Figs and Fig Wasps! ● Reproductive Development ○ Default flowering ○ Many mechanisms evolved to delay flowering (Arabidopsis) ○ Juvenile → Adult transition induced by overexpression of the flowering gene ■ LFY (Leafy) cloned from Arabidopsis → implanted into aspen → caused flowering to occur within weeks instead of YEARS ■ LFY mutant – lots of foliage/flowers ■ LFY gene expression very important in the flowering process ■ These genes are transcription factors (promoting region is activated by basic transcription machinery and LFY gene is then expressed) ● CONSTANS (CO) Pathway ○ Shows how amount of sunlight = changes in gene expression and flowering process in plants ○ Long day plants: ■ Clock genes – genes that regulate the expression of genes during certain times of day ■ Light = constans is made (can be made both day and night) + prevents it from being broken down ■ Longer light cycle = more constans buildup → turns on next step ■ Constans protein = transcription factor ■ Constans → FT gene activated → activates FT protein chain → FT (transcription factor for FD in SOC1) turns on AP1 and SOC1 → turns on different flowering genes in plants ○ Double repression – when a factor sets off a chain reaction in gene expression ■ Tempdependent pathway = vernalization → blocks flowerrepressing gene → activates flowerpromoting genes ■ Autonomous pathway = Autogene expression → blocks flowerrepress gene → activates flowerpromo genes ■ Gibberellindependent pathway = Gibberellin → LFY + flowerpromo genes activated → ABCDE floral organ identity genes → floral organ development ● ABC Model & modifications ○ Expresses the four parts of a flower in three gene classes ■ Class A genes sepals ■ Class A + Class B Petals ■ Class B + Class C Stamens ■ Class C genes Carpels ○ Mutant flower = no function ■ Amutant flower = Carpels → stamens → carpel (missing gene class A) ■ Bmutant flower = Sepals → Carpels (missing gene class B) *Note: Please DO NOT return after purchase. Thank you!* ■ Cmutant flower Sepals → Petals → Sepals (missing gene class C) ○ Original thought was that flower whorls were originally derived from leaves ○ Question – why were sepals present instead of leaves when a mutation occurred? ■ Answer – Class D/E genes were present to make additional floral parts in place of petals ● Pollination Incompatibility ○ Increases outcrossing ○ Pollen and stigma recognize each other as self → pollen tube locked ○ Controlled by many alleles at S locus (selfincompatibility) ○ 2 types: ■ Gametophytic selfincompatibility (petunias) ● Depends on haploid S locus (pollen) + diploid S locus (stigma) ● Growth tube stops before reaching embryo sac ■ Sporophytic selfincompatibility (broccoli) ● If alleles match in stigma and pollen → haploid pollen will NOT germinate ● Double Fertilization ○ Only in angiosperms ○ Double fertilization: ■ Fertilization of egg ■ Formation of endosperm (fusion with polar nuclei → 3n endosperm) ● Embryonic Development ○ Begins once egg cell fertilized ○ Growing pollen tube enter angiosperm → releases two sperm cells → one sperm + egg = zygote → other sperm + central cell = endosperm ○ 1st zygote asymmetrical ■ Small cell = keeps dividing to form embryo ■ Large cell = keeps dividing to form suspensor (transports nutrients to embryo from endosperm) ■ Rootshoot axis forms ● Near suspensor = root ● Cells at other polar end = shoot ● Body Plan ○ 3D shape arises by regulating cellpattern divisions ■ Vertical axis/radial axis est. at a very early stage ■ Globular stage cells form a tight ball ○ Apical meristems form, three basic tissues arise ■ Dermal forms cover for plants ■ Ground tissues that perform all other functions that dermal and vascular tissues don’t cover ■ Vascular transportation of nutrients and water all around plants ■ Organized radially from rootshoot axis
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