Flowering Plants

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Anthophyta – Flowering Plants: 

Anthophyta – Flowering Plants

Systematics: 

Systematics Phylum Anthophyta characterized by flowers Double fertilization produces triploid endosperm and zygote Xylem mostly contains vessel elements Ovary developes into fruit

Systematics (cont.): 

Systematics (cont.) Amborella the most primitive known flowering plant Uses tracheids instead of vessel elements Unisexual flowers, with spirally arranged parts

Systematics (cont.): 

Systematics (cont.) Magnoloids also seem to be primitive Flower parts Nucleic acids Still unsettled – water lilies and “paleoherbs” are contenders as well Monocots and eudicots are derived

Monocots vs. dicots: 

Monocots vs. dicots Monocots One cotyledon Flower parts in threes Pollen is monoaperturate Parallel venation Primary vascular bundles scattered Usually no secondary growth

Monocots vs. dicots: 

Monocots vs. dicots Eudicots Two cotyledons Flower parts in fours or fives Pollen triaperturate Net venation Primary vascular bundles in ring Secondary growth common

The Flower: 

The Flower Determinate shoot with sporophylls Carpel is definitive structure – it is the “vessel” of angiosperms (“vessel seed”) Contains ovules, which develop into seeds Flowers clustered in various ways Stalk of single flower or inflorescence is peduncle Stalk of individual flower in inflorescence is pedicel Part of stalk to which floral parts attached is receptacle

Flowers (cont.): 

Flowers (cont.) Most flowers have modified sterile leaves called sepals and petals Sepals collectively = calyx Usually green, thick Petals collectively = corolla Usually colored, thin Calyx and corolla together = perianth

Flowers (cont.): 

Flowers (cont.) Fertile parts of flowers called stamens and carpels Stamens collectively = androecium Microsporophylls Consists of filament and two-lobed anther Anther contains four microsporangia (pollen sacs) borne in 2 pairs (defining feature of angiosperms) Carpels collectively = gynoecium Megasporophylls Flowers may have more than one carpel Individual carpels or fused carpels called pistil Pistil differentiated into ovary, style and stigma In fused carpels, ovary partitioned into locules

Placentation: 

Placentation Placenta is part of ovary where ovules originate & remain attached until mature Arrangement of placenta is placentation Parietal – placenta on ovary wall or extensions Axile – placenta on central column of partitioned ovary Free central – placenta on central column of non-partioned ovary Basal – single ovule at base of ovary Apical – single ovule at apex of ovary

Flower variations: 

Flower variations Perfect flowers have both stamens and carpels Imperfect flowers are missing either stamens or carpels = unisexual Carpellate (Pistillate) flowers have carpels Staminate flowers have stamens Monoecious plants have staminate and carpellate flowers on one plant Dioecious plants have staminate and carpellate flowers on separate plantes

Flower variations (cont.): 

Flower variations (cont.) Four floral whorls (calyx, corolla, etc.) If all are present, the flower is complete If one or more is missing, the flower in incomplete Spiral vs. whorled Joining of floral parts Connation – parts of same whorl united Adnation – parts of different whorls united If parts not joined, prefixes apo- or poly- used If parts are joined, prefixes syn- or sym- used

Flower variations (cont.): 

Flower variations (cont.) Sepals, petals and stamens vary in points of attachment on floral axis Attached to receptacle below ovary – superior Attached above ovary – inferior Intermediates as well (still considered inferior or partially inferior) Insertion points Hypogynous – perianth and stamens on receptacle below ovary Epigynous – perianth and stamens above ovary Perigynous – stamens and petals adnate to calyx and forming short tube around ovary

Flower variations (cont.): 

Flower variations (cont.) Symmetry Radial symmetry (members of each whorl alike) – regular (actinomorphic) flowers Bilateral symmetry (members of a whorl may be different from other members) – irregular (zygomorphic) flowers

Angiosperm life cycle: 

Angiosperm life cycle The “male” story Microsporogenesis Sporogenous cells develop in anther Sterile cells surround the pollen sacs Form tapetum, which nourishes growing microspores Sporogenous cells form microsporocytes Microsporocytes divide meiotically to produce microspores Pollen grain features formed Exine – sporopollenin Intine

Angiosperm life cycle: 

Angiosperm life cycle The “male” story continues Microgametogenesis Microspore (n) divides mitotically to form two cells Large tube cell Smaller generative cell Most pollen shed in this two-celled stage Generative cell divides mitotically to form 2 sperm cells

Angiosperm life cycle: 

Angiosperm life cycle The “female” story Ovule structure Funiculus Nucellus enclosed by integument(s) Micropyle Megasporogenesis Early in development of ovule, single megaspore (2n) forms Megaspore divides meiotically to produce 4 haploid megaspores arranged linearly 3 of the 4 megaspores disintegrate, leaving the megaspore farthest from the micropyle

Angiosperm life cycle: 

Angiosperm life cycle The “female” story continues Megagametogenesis Three mitotic divisions produce 8 nuclei One group of 4 is at chalazal end of developing gametophyte, the other is at the micropylar end One nucleus from each group migrates to center; these two nuclei are polar nuclei The 3 nuclei at micropylar end become egg apparatus: an egg cell and two synergids The 3 nuclei at chalazal end are the antipodals

Angiosperm life cycle: 

Angiosperm life cycle Megagametogenesis continues Cell walls form around egg apparatus cells and antipodals, creating 7-celled, 8 nucleate embryo sac – the female gametophyte Variations on this theme; lily is an example Two 4-nucleate stages, with triploid cells at chalazal end

Angiosperm life cycle: 

Angiosperm life cycle Double fertilization Pollination Stigma is glandular, receives and nourishes pollen Style contains transmitting tissue, through with or by which the pollen tube grows towards ovule Pollen enters ovule through micropyle, and then penetrates embryo sac via one of the synergids Fertilization One of the sperm fuses with egg, making zygote The other fuses with the two polar nuclei, forming triploid endosperm In Gnetophytes (gymnosperm), the second fertilization produces a second embryo

Seed and fruit formation: 

Seed and fruit formation Triploid endosperm nucleus may divide mitotically to produce nutritive tissue (endosperm) Alternatively, the nucellus may divide to produce nutritive perisperm Cotyledon(s) serve either to store food obtained from the other nutritive tissues, or to serve as a conduit for those nutrients to embryo Integuments form seed coat

Seed and fruit formation: 

Seed and fruit formation Ovary wall (the pericarp) thickens and forms fruit Often layered Exocarp (outer layer), mesocarp (middle layer), and endocarp (inner layer); or sometimes just exocarp and endocarp Other parts of flower may also be incorporated in fruit as it developes

Evolution of flower: 

Evolution of flower Early flower Probably didn’t have distinct sepals and petals In water lilies, petals evolved from sepals In most angiosperms, petals evolved from stamens Stamens had diverse function and structure In magnoliids, stamens scented, broad, brightly colored Some become nectaries in other angiosperms Carpels unspecialized in early angiosperms

Evolution of flower: 

Evolution of flower Evolutionary trends in flower Flowers with few to many parts, indefinite in number flowers with few parts, definite in number Floral whorls declines from four to three, two or even one Ovary becomes inferior; perianth includes calyx and corolla Radial symmetry bilateral symmetry

Mechanisms of pollination: 

Mechanisms of pollination Outcrossing Structural Dioecious plants In monoecious plants, staminate and carpellate flowers in different places, and may mature at different times Dichogamy – stamens and carpels mature at different times, even if in same flower Protandrous Protogynous Genetic self-incompatibility Gametophytic self-incompatibility Sporophytic self-incompatibility

Mechanisms of pollination: 

Mechanisms of pollination Outcrossing Pollinators Flowers and insects have co-evolved! Beetle-pollinated flowers are typically broad (with landing platforms), dull-colored, and strong odor Bee and wasp-pollinated flowers typically blue or yellow with nectar guides Orchids and other flowers may parasitize bees Bees may parasitize legumes Moth- and butterfly-pollinated flowers typically have long corolla tube Night pollinators vs. diurnal ones

Mechanisms of pollination: 

Mechanisms of pollination Outcrossing Pollinators Flowers and insects have co-evolved! Fly-pollinated often dull-colored, smell like rotting flesh; can also resemble other types Bird pollination Flowers often large, red or orange and odorless, lots of nectar inaccesible to other pollinators Bat pollination Flowers dull-colored, strong odor, lots of nectar, protein-rich pollen

Mechanisms of pollination: 

Mechanisms of pollination Outcrossing Wind pollination – flowers small, no nectar, dull color, available to wind Water pollination – pollen filiform or released in chains Self-fertilization Common in temperate and arctic areas Flowers small, inconspicuous, may not even open!

Mechanisms of pollination: 

Mechanisms of pollination Floral pigments Flavenoids Anthocyanins Flavonols Betacyanins

Fruits: 

Fruits Nomenclature Fruit is mature ovary Fruit which includes additional floral parts is an accessory fruit Parthenocarpic fruits have no seeds Simple fruit developes from one carpel or several united carpels Aggregate fruits come from several carpels on one gynoecium Multiple fruits consist of gynoceia of more than one flower

Fruits: 

Fruits Simple fruits Berries (ex. Tomato) – one to several carpels each with many seeds, inner wall fleshy Drupes (ex. Peach) – one to several carpels each with one seed, inner layer stony and adheres to seed Pome (ex. Apple) – comes from compound inferior ovary; fleshy part developes from perianth. Endocarp is tough.

Fruits: 

Fruits Simple fruits (cont.) Dry simple fruits Dehiscent Follicle – comes from single carpel that splits down one side (milkweed) Legume – like follicle but splits down both sides Silique – comes from two fused carpels; two sides split leaving seeds on central column Capsule – from compound ovary Indehiscent Achene – single seed free in cavity Winged achene – samara Caryopsis – grasses; seed attached to wall Cypsela (asters) – achene-like but comes from inferior ovary Nut – resemble achenes but derived from compound ovary and have stony wall Schizocarp (maple) – fruit splits at maturity into two or more one-seeded portions

Fruits: 

Fruits Dispersal Wind Small seeds (orchids) Parachutes (dandelions) Whole plant (tumbleweed) Shoot seeds (Impatiens) Water

Fruits: 

Fruits Dispersal Animals Eat the fruit, or some portion Ripening Elaiosomes and ants Adhere to fur, feathers, etc.

Biochemical coevolution: 

Biochemical coevolution Secondary metabolites Probably evolved to protect plant from herbivores Some herbivores become specialists on such plants Mimicry systems Response to feeding Protease inhibitors Hormone mimics Attract predators or parasites

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