Green Plants - Chapter 30

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Geological TIme Scale

First land plants - 525 MYA

Why Move to Land?

1. More light
2. Minerals - plants were the first "miners"
3.Symbiotic association with fungi - mychorrhizae - mineral and water uptake

Mychorrhizae

Mineral and water uptake

Major adaptations to life on land

1. prevention of water loss - cuticle/stomata
2. structural support to resist gravity - vascular system to move water and photosynthate
3. new reproductive strategies - symbiotic assoication with emerging animals
4. prevention of becoming a food source for emerging animals
5. symbiotic assoication with fungi - mycorrhizae. Absolutely important for extracting minerals from the soil.

Defining Plants

All green algae and land plants shared a common ancestor a little over 1 BYA. Kingdom Virdiplantae. A single species of freshwater green algae gave rise to the entire terrestrial plant lineage.

Clade

a monophyletic group of organisms that share homologous features dderived from a commmon ancestor.

Chlorophytes

Never made it to land

Charophytes

Made it to land. Sister to all land plants.

Land Plants

Have multicellular haploid and diploid stages. Trend toward more diploid embryo protection. Trend toward smalled haploid stage. Diploid stage dominates life cycle and larger.

Why diploid dominance?

1. About 550 million years ago, UV radiation was still high - water protected.
2. Coming to land menay DNA damage. being diploid - could mask DNA damage in recessice gene on alternate chromosome.
3. Larger number of alleles exist in gene pool - greater diversity

Multicellular diploid stage

Sporophyte - 2N.
Produces haploid spores by meiosis. Diplois spore mother cells (sporocytes) undergo meiosis by sporangia. Produces 4 haploid spores and first cells of gametophyte generation.

Multicellular haploid stage

gametophyte - N
Spores divide by mitosis. Produces gametes by mitosis. Gametes fuse to form diploid zygote. First cell of next sporophyte generation.

All land plants are haplodiplontic.

Relatice size of generation vary.

Moss - large gametophyte. Small, dependent sporophyte.

Angiosperm-small dependent gametophyte, large sporophyte.

Green Algae

Two distinct lineages. Chlorophytes and Streptophytes

Chlorophytes

Gave rise to aquatic algae. Closely resemble land plants.

Sterptophytes

Gave rise to land plants.

Charophytes

Clade of streptophytes. Also green algae. Distinguised from chlotophytes by close phylogenetic relationship to land plants. Haplontic life cycles. Evolution of diplontic embryo and haplodiplontic life cycle occured after move to land.

2 Candidate Charophyta clades

Charales and Coleochaetales. One species of Chara must have successfully inched its way onto land through adaptations to drying

Bryophytes

Closest living descendants of the first land plants. Called nontracheophytes because they lack tracheids. Do have other conducting cells. Mychorrhizal assoiciations important enhancing water uptake.

Gametophyte

conspicuous and photosynthetic. Sporophytes - small and dependent. Requires water for sexual reproduction.

Mosses

phylum Bryophyta

Gametophytes consist of small, leadlike strucutres around a stemlikek axis. Not true leaves - no vascular tissue. .

Anchored to substrate by rhizoids.

Tracheophyte Plants

Cooksonia, the first vascular land plant.

Appeared about 420 MYA. Only a few centimeters tall, no roots or leaves. Homosporous - only one type of spore.

Tracheophytes

Vascualar plants include seven extant phyla grouped in three clades.
1. Lycophytes (club mosses)
2. Pterophytes (ferns, whisk ferns, and horsetails)
3. seed plants

Xylem

Conducts water and dissolved mineral upward from the roots

Phloem

Conducts sucrose and hormones throughout the plants

Lycophytes

Worldwide distribution - sbundant in tropics. Lack seeds. Superficially resemble true mossess.

Limitations of Early Land Plants

Stems - early fossils reveal stems but no roots or leaves. Lack of roots limited early tracheophytes

Roots- provide transport and support. Lycophytes diverged before true roots appeared.

Leaves- Increased surface area for photosynthesis. Evolved twice - Euphylls (true leaves) found in ferns and seed plants and Lycophylls found in seed plants

Pterophytes

Phylogenetic relationship among ferns and their relatives is still being sorted out. Common ancestor gave rise to 2 clades. All form antheridia and archegonia.

Whisk ferns

Found in tropic, Sporophyte consists of evenly forking green stems without true leaves or roots. Some gametophytes develop elements of vascular tissue.

Horsetails

All living species are homosporous. Ribbed, jointed photosynthetic stems that arise from branching rhizomes with roots at nodes. Silica deposits in cells - "scouring rush" of pioneer days.

Ferns

Most abundant group of seedless vascular plants. Coal formed from forest 300 MYA. Conspicuous sporophyte and much smaller gametophyte are both photosynthetic. Fern life cycle differs from that of moss. Much greter devlopment, independence and dominance of ther fern's sporophyte. Gametophyte lacks vascular tissue.

Fern Reproduction

Produce distinctive sporangia in clusters called sori on the back of the fronds. Diplois spore mother cells in sporangia produce haploid spores by meiosis. Spores germinate into gametophyte. Rhizoids but not true roots - no vascular tissue. Flagellated sperm.

Evolution of Seed Plants

Appeared 305-465 MYA. Evolved from spore bearing plants known as progymnosperms.

Success attributed to evolution of seed

Protects and provides food for embryo. Allows the clock to be stopped to survive harsh periods before germinating, later development of fruits enhanced dispersal.

Seed-internal fertilization, escape from water

Embryo protected by integument (can escape desiccation and hardened seed coat), megasporangium divides meiotically inside ovule to produce haploid megaspore, megasporie produces egg that combines with sperm to form zygote and also contains food supply for embryo.

2 kinds of gametophytes

Male - pollen grains, dispersed by wind or a pollinator, no need for water.

Female - devlop within an ovule, enclosed within diploid sporophyte tissue in angiosperms.

Gymnosperms

Plants with naked seeds.

Coniferophytes
Cycadophytes
Gnetophytes
Ginkgophytes

All lack glowers and fruits of angiosperms, all have ovule exposed on a scale.

Conifers

phylum Coniferophyta

Most familiar gymnosperm phylum.

Pines, sprices, firs, cedars and others. Found in colder and sometimes drier regions of the world. Conifers are sources of important products. Timber, paper, resin and taxol (anti-cancer)

Pines

Example of Conifer. More than 100 species, all in Northern hemisphere. Leaves have thick cuticle and recessed stomata to retard water loss. Leaves have canals with resin to deter insect and fungal attacks.

Pine Reproduction

Male gametophytes (pollen grains) - develop from microspores in male cones by meiosis.

Femal pine cones form on the upper branches of the same tree. Female cones are larger and have woody scales. Two ovules develop on each scale. Each contain a megasporangium. (each will become a female gametophyte)

Pine Reproduction

Female cones take 2 or more season to mature. During the first season the pollen grains drift down between open scales. (pollen grains drawn down into micropyle, scales close).

A year later, female gametophyte matures. Pollen tube is digesting its way thorugh and mature male gametophyte has 2 sperm.

15 months after pollinaiton, pollen tube reaches archegonium and discharges contents. One sperm united with egg=sygote. Other sperm degenerates.

Cycads

phylum Cycadophyta

Slowing growing gymnosperms of tropical and subtropical regions. Sporophytes resemble palm trees. Female cones can weigh 45 kg. Have the largest sperm cells of all organisms.

Gnetophytes

phylum Gnetophyta

Only gynmonsperm with vessels in their xylem. Contain three genera

Welwitschia
Ephedra
Gnetum

Ginekgophytes

phylum Ginkophyta

Only one living species remains - now a cultivar. Ginkgobiloba. Flagellated sperm, Dioecious (male and female reproductive structures form on different trees)

Angiosperms

Flowering plants, Ovules are enclosed in diplois tissue at the time of pollination. Carpel, a modified leaf that covers seeds, develops into fruits.

Angiosperm origin

Origin as early as 145-208 MYA.

Oldest known angiosperm in the fossil record is Archaefructus. Closest living relative to the orginal angiosperm is Amborella.

Flower Morphology

Modified stems bearing modified leaves. Primordium develops into a bud at the end of a stalk called the pedicel. Pedicel expands at the tip to form a receptable, to which other parts attach. Flower parts are organized in circles called whorls.

Carpel's 3 regions

Ovary - swollen base containing ovules

Stigma - tip where pollen lands

Style - neck ot stalk

Megaspore

Single megaspore mother cell in ovule undergoes meiosis. Produces 4 megaspores, daughter nuclei divide to produce 8 haploid nuclei and integuments become seed coat.

Pollen production

occurs in the anthers. It is similar but less complex than female gametophyte formation. Diploid microspore mother cells undergo meiosis to produce four haploid microspores Binucleate microspores become pollen grains.

Pollination

Mechanical transfer of pollen from anther to stigma. May or may not be followed by fertilization. Pollen grains devlop a pollen tube that is guided to the embryo sac. One of the two pollen grain cells lag behind, this generative cell divided to produce two sperm cells and no flagella on sperm.

Double fertilization

One sperm united with egg to form the diploid zygote. Other sperm united with the two polar nuclei to form the triploid endosperm. Seed may remain dormant for many years.

Ecological Propertoes of C. americana

1. lacking chlorophyll, but possessing all other traits of Angiosperms - flowers, seeds.
2. parasitic on roots of plants, but causes the host no discernable damage.
3. DNA has been sequenced and the genes for photosynthesis proteins are lacking
4. achlotophyllus/parasitic life style arose by mutation

Medicinal Properites of C. americana

1. Astringent medical qualities
2. Used to treat hemorrhaging and headaches
3. used by Naticve Ameircans to reduce symptoms of menopause - hence its name "squaw root"
4. The name "cancer root" refers to its palliatice qualities - no known cancer cure properties.

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