SEED PLANTS II The Flowering Plants (Anthophyta)

Anthophyta

Phylum Anthophyta (Angiosperms) Constitutes ~300,000 species (Gymno. 720 spp) Most recently evolved & most diverse group Divided into many groups: Basal Angiosperms Magnoliids (~8500) Eudicotyledones (dicot) Monocotyledones (monocot) Most living vascular plants are angiosperms Angiosperms are characterized by a unique organ system called the flower It seems like each of the mono and the eudicots is a monophyletic group

Phylogeny of Angiosperms Basal angiosperms Each branch of the tree can be called a clade or lineage. Amborella is considered an intermediate between Gymnosperms and Angiosperms. It consists of one species in New Caledonia. This is a shrub with small flowers and lacks vessels (has only tracheids). The early (basal) angiosperms have alternate and simple leaves, flowers with multiple whorls of tepals ( a common term for sepals and petals when they look alike), stamens are undifferentiated into filaments and anthers), and many separate carpels. Also carpels are not completely closed. Amborella and Nymphaeales lack vessels, Austroballeyales has simple vessel. Carpel is a modified leaf that protects ths developing seed. It includes the stigma, style and an ovary. Fusion

Fusion of Carpel secretion fusion From Endress & Igersheim, 2000

Characteristics of Angiosperms Double fertilization: egg + sperm produce zygote (2n) egg + 2nd sperm produce endosperm (3n) Mostly closed carpels: enclose ovule Reduced gametophytes (pollen grain, embryo sac) Sieve tubes and companion cells (phloem) Vessels (xylem) Stamens with 2 pairs of pollen sacs Chemical evolution!

Refinements in vascular tissue, especially xylem, probably played a role in the enormous success of angiosperms in diverse terrestrial habitats. Like gymnosperms, angiosperms have long, tapered tracheids that function for support and water transport. Angiosperms also have fiber cells, specialized for support, and vessel elements (in most angiosperms) that develop into xylem vessels for efficient water transport.

Amborella (Basal angiosperms) Fruit Scott Zona http://www.amborella.org/ mailto:stephens@cats.ucsc.edu Notice the female flowers have 0-several stamenoids (sterile stamens). This is a genus of one species native to New Caledonia (an Island E of Australia) Scott Zona The plant is dioecious. Female flowers with 5-6 carpels (a). Male flowers 10-25 stamens (b).

Magnolia (Magnoliids) Follicle is a dehiscent fruit from a single carpel. Fruit: aggregate follicle

Tulip (Magnoliids)

Differences Between Monocot & Eudicot Embryo with single cotyledon Pollen with a single furrow or pore* Flower parts in multiples of three Major leaf veins parallel Stem vascular bundles scattered Have fibrous roots Secondary growth absent EUDICOT Embryo with two cotyledons Pollen with three furrows or pores Flower parts in multiples of four or five Major leaf veins reticulate Stem vascular bundles in a ring Have taproots Secondary growth often present Fibrous roots: many small roots of same size originate from the base of monocot stem because their primary root is short-lived. Taproot: the main embryonic root giving rise to smaller later roots as in dicot Adventitious root: roots from places other than root Magnoliids have pollen like Monocot

Pollen of Horse chestnut Eudicot like these have pollen with 3 apertures A Grass Pollen Pollen of Horse chestnut

Flower: the main feature of angiosperms (= Carpel)

The Flower Perianth: Sepals & petals collectively Androecium: stamens collectively Gynoecium: pistils collectively

Types of Flowers Complete flower: has all 4 floral parts Incomplete flowers: missing a floral part(s) Perfect Flower: bisexual Imperfect flower: unisexual flowers Staminate flowers: have only the stamens Pistillate (carpellate) flowers: have only pistils Monoecious plants: separate staminate and pistillate flowers on the same plant Dioecious plants: either staminate or pistillate flowers Monoecious: (grasses) Dioecious (willows)

Zygomorphic: floral parts are different (bilaterally symmetrical) Floral symmetry: Actinomorphic flower: floral parts are of similar shape & size (radially symmetrical) Zygomorphic: floral parts are different (bilaterally symmetrical) Inflorescence: A cluster of flowers with a definite arrangement Fertilization: the fusion of two gamete nuclei to produce a diploid zygote Pollination: transfer of pollen from the anther to the stigma Pollen transferred within the same flower is called self-pollination, and the species is an in-breeder Pollen transferred to a different flower is called cross-pollination and the species is out-breeder

Example of Monocot Flower: Lilium sp.

Example of a Dicot Flower Hibiscus moscheutos

Dicot Stamens H. moscheutos is a Dicot, with five petals and five sepals. It grows naturally in cattail marshes along the shore of Lake Ontario and along the Hudson River between Albany and New York City. The showy pink petals are ten or more centimeters long. The style divides into five branches near its tip; each branch bears a capitate (hear-like) stigma It is a member of the Mallow Family (Malvaceae) As with all members of the Malvaceae, the numerous stamens are fused by their filaments to form a tube around the style. Stigmas

Hibiscus II Filament tube Style Ovary Ovules A flower has been split open to show the ovary with ovules contained inside The flower remains open for only one day After the corolla, stamens, and style wither and fall away, the ovary develops into a capsule that splits open to release the seeds.

Angiosperm Life Cycle Sperm Egg Fertilization 1n 2n Zygote Meiosis Pollen Embryo sac Megagametogenesis Microgametogenesis Sperm Egg Fertilization Microspores Megaspores Micosporogenesis Megasporogenesis 1n 2n Zygote Meiosis Sporophyte

Development of Pollen Microsporogenesis: the development of microspore mother cell (microsporocyte) into microspores This involves meiosis

Liliy Flower

Microsporocytes Microsporocyte is a single diploid cell (2n) that undergoes meiosis to produce 4 haploid cells (microspores or male spores) Tapetum is the non-reproductive tissues that provide nutrition to the developing spores

Microsporocyte undergo Meiosis The microspore mother (2n) cells undergoing meiosis. See cells in various stages of meiosis.

Tetrads of Microspores Pollen tetrads Microspores At end of meiosis 4 haploid (1n) male spores are produced 4 microspores were produced by meiosis Microsporogenesis is complete

Development of Pollen Microgametogenesis: the development of microspores into male gametophyte (pollen grain) This involves mitosis

Mature Male gametophyte Microspores underwent mitosis to produce male gametophytes

Mature Pollen grain The tube nucleus produced the pollen tube The generative cell produced two sperm nuclei

Development of Female Gametophyte Megasporogenesis: the megasporocyte (megaspore mother cell) develops into megaspores by meiosis

Lilium Ovary Cross section of lilium ovaries.

Megasporocyte Before Meiosis The Megasporocyte or megaspore mother cell is a single diploid cell (2n) which undergoes meiosis to produce 4 haploid cells (megaspore or female spores).

Two-nucleate Stage (formed by meiosis)

Four-nucleate Stage (formed by meiosis) This survives others die The result of meiosis is 4 haploid cells. Only one of these cells survives. In the next slide you would see the surviving female spore

Functional Megaspore Megasporogenesis is complete This is the megaspore or the female spore (1n) which develops into the female gametophyte (by mitosis). See next sildes.

Development of Female Gametophyte Megagametogenesis: the megaspore develops into mature female gametophyte (embryo sac) by mitosis Three mitotic divisions follow

First mitotic Division: 2-nucleate embryo sac

2nd Mitotic Division: 4-Nucleate embryo sac

3rd Mitotic Division: 8-Nucleate embryo sac

8-Nucleate embryo sac 2 of 4 Antipodals Egg & 2 synergids

Pollination & Fertilization Pollen Tube Sperms Pollination & Fertilization

Double Fertilization