Lecture 15 Botany & Mycology: plant and fungal diversity Flashcards
Plant diversity
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- Land Plants and Terrestrial Life
- Green algae & land plants shared a common ancestor > 1 BYA
- Multicellular autotrophs adapted to land
A. Origin of Land Plants – Green algae
- Green algae & land plants shared a common ancestor > 1 BYA
- The green algae split into two major clades
– Chlorophytes – Never made it to land
– Charophytes – Sister to a
Key traits appear in nearly all plants
but are absent in the charophytes
● Alternation of generations
● Walled spores produced in
sporangia
● Apical meristems
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B. Transition from water to land
- Limiting water loss and control of as exchange
- Limit UV damage to DNA
- Water transport through plant
- Resistance to effects of wind and gravity
- Protection and dispersal of reproductive structures
- Life cycles promoting genetic diversity
Adaptations to terrestrial life
* Protection from desiccation - Waxy cuticle and stomata
* Moving water using tracheids - Xylem and phloem to conduct water and food
* UV radiation caused mutations - Shift to a dominant diploid generation
* Haplodiplontic life cycle
– Multicellular haploid and diploid life stages
– Humans are diplontic
C. Alternation of Generations
Multicellular haploid stage – gametophyte
– Spores divide by mitosis to produces gametes
– Gametes fuse to form diploid zygote (1st cell of next sporophyte generation)
Multicellular diploid stage – sporophyte
– Produces haploid spores by meiosis
– Diploid spore mother cells (sporocytes) undergo meiosis in sporangia
* Produce 4 haploid spores
* First cells of gametophyte generation
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Highlights of plant evolution
- Origin of plants (non vascular) - Bryophytes
- Origin of vascular plants (seedless): Lycophytes and Monilophytes
- Origin of seed plants (angiosperm and gymnosperm)
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Bryophytes
- Closest living descendants of the first land plants
- Called nonvascular plants - they lack tracheids
- Simple organisms divided in 3 clades
– Hornworts
– Liverworts
– Mosses - Adaptations to living on land
– Short (<7cm) – lack vascular system
– Lack roots - Mycorrhizal associations important in enhancing water uptake
– Gametophyte – dominant generation (photosynthetic)
– Require water for sexual reproduction
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Vascular Plants
- Tracheophytes - Seedless Vascular Plants
- Evolved Roots, Stems, and Leaves
- Vascular tissues
– Xylem - Conducts water and dissolved minerals upward from the roots
– Phloem - Conducts sucrose and hormones throughout the plant - Enable enhanced height and size in the tracheophytes
- Life cycle is dominant sporophyte
- Cuticle and stomata also found in land plants
- Divided into three clades
– Seedless vascular - Lycophytes (club mosses)
- Monilophyta (ferns, whisk ferns, and horsetails)
– Seed plants
Major plant innovations
Stems - Early fossils reveal stems but no roots or leaves
– Lack of roots limited early tracheophytes
* Leaf - Increase surface area for photosynthesis
Higher stomatal densities favored larger leaves with a photosynthetic advantage that did not overheat
Evolved twice
o Euphylls (true leaves) found in ferns and seed plants
o Lycophylls found in seed plants
* Roots - Provide transport and support
– Lycophytes diverged before true roots appeared
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The Evolution of Seed Plants
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The Evolution of Seed Plants
- Seed plants first appeared 305–465 MYA
– Evolved from spore-bearing plants known as progymnosperms - Success attributed to evolution of seed: embryo + nutrient
– 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 plant life cycles are sporophyte-dominated
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Seed vs spores
Seeds provide evolutionary advantages over spores
* Seeds are multicellular; spores are single cells
* Seeds can remain dormant for years until conditions are
favorable for germination, whereas spores are shorter-lived
* Seeds have stored food to nourish growing seedlings; spores
do not provide nourishment to gametophytes
* Seeds can be transported longer distances by wind or
animals, but spores usually drop closer to the parent plant
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Seed plants produce 2 kinds of gametophytes
- Male gametophytes - Pollen grains
– Dispersed by wind or a pollinator
– No need for water - Female gametophytes - Develop within an ovule
– Enclosed within diploid sporophyte tissue in angiosperms
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Gametophyte-sporophyte relationships in different plant groups
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Two types of seed plants
Gymnosperm: plants with “naked seed”
- seeds are not enclosed in chambers
Angionsperm:seeds develop inside chambers
-90% of living plants
-consists of all flowering plants
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Defining Fungi
- Mycologists - 1.5 million fungal species
- Most are multicellular - mycelium
- Unicellular or single-celled (yeast)
- Sexual or asexual
- Heterotrophs and absorb nutrients from surroundings
- Hydrolytic enzymes to break down complex molecules into smaller
organic compounds
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Unicellular Yeast
- Unicellular ascomycetes
- Most reproduce asexually by budding
- Yeasts can ferment carbohydrates
– Break down glucose into ethanol and CO2
– Used to make bread, beer, and wine
– Saccharomyces cerevisiae - long-standing model system for genetic research
– First of the eukaryotes to be genetically engineered extensively
– Saccharomyces cerevisiae first eukaryote to have genome sequenced
– Other fungi are being sequenced and studied which may affect our
understanding of their evolution
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A- Structure - Fungal mycelium
- Mycelium – mass of connected hyphae
– Grows through and digests its substrate - Fungal cell walls include chitin
– Also found in the hard shells (exoskeletons) of arthropods
– Both fungi and animals store glucose as glycogen - Multicellular fungi consist of long, slender filaments called hyphae
– Some hyphae are continuous called coenocytic hyphae
– Others are divided by septa – septate hyphae - Cytoplasm flows throughout hyphae
– Allows rapid growth under good conditions
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C - Cell division
- Fungi have an unusual mitosis
– Cell is not relevant unit of reproduction
– Nuclear envelope does not break down and re-form
– Instead, the spindle apparatus is formed within it - Fungi lack centrioles (except in chytrids)
– Spindle pole bodies form mitotic spindles
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D -Reproduction
- Capable of both sexual and asexual reproduction
- Sexual reproduction
– Fusion of two haploid hyphae of compatible mating types - In some fungi, fusion immediately results in a diploid (2n) cell
- Others, have a dikaryon stage (1n + 1n) before parental nuclei form diploid nucleus
– May form motile zoospores, zygosporangia, basidia, or asci - Spores - most common means of reproduction among fungi
– May form from sexual or asexual processes
– Most are dispersed by wind or insects
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Generalized life cycle of fungi
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E. Nutrition
- Heterotrophs - obtain carbon and energy from the digestion of polymers
- External digestion- secrete digestive enzymes into surroundings
- Absorb the organic molecules produced by this external digestion
– Decomposers – food = dead plants and animals
– Parasites - invade the living cells of their hosts and absorb nutrients directly - Fungi can break down cellulose and lignin
– Decompose wood
– Some fungi are carnivorous
majority of dead plants and
plant-based materials are
decomposed by fungi
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Ecology of Fungi
- Principal decomposers in the biosphere (also bacteria)
- Break down cellulose and lignin from wood
– Releases carbon, nitrogen, and phosphorus
– Makes the elements available to other organisms
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Fungal relationships
- Fungi symbioses
– Obligate symbiosis – essential for fungus survival
– Facultative symbiosis – nonessential (fungus can survive without the partner) - Three kinds of Interactions:
– Pathogen (harm host : disease) or parasites –harm host : no disease
– Commensal relationships benefit one partner but does not harm the other
– Mutualistic relationships benefit both partners
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Mycorrhizae
- Mutualistic relationships between fungi and plants
- Found on the roots of about 90% of all known vascular plant species
- Function as extensions of root system - Increase soil contact and absorption
– allow plants to grow in the infertile soils - Two principal types
– Arbuscular mycorrhizae - Hyphae penetrate the root cell wall but not plant membranes
– Ectomycorrhizae - Hyphae surround but do not penetrate the root cells (pine, oaks)
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Animal mutual symbioses
- Ruminant animals host neocallimastigamycete fungi in their gut
– Fungus degrades plant materials with high cellulose and lignin content
– Host provides nutrient-rich environment - Leaf-cutter ants have domesticated fungi which they keep in
underground gardens
Obligate symbiosis
– Ants provide fungi with leaves
– Fungi are food for the ants
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Fungal Parasites
- Fungal species cause many diseases in plants
– Among most harmful pests of living plants
– Can also spoil harvested or stored food products
– Secrete toxic substances in food - Cause billions of dollars in agricultural losses
- In Plants - Fungi may secrete substances making food unpalatable,
carcinogenic, or poisonous - Aspergillus flavus – aflatoxin
- Ustilago maydis – edible corn smut (not harmful to animals)
- In animals - difficult to treat (close phylogenetic relationship with animals)
– Candida – thrush; vaginal infections
– Pneumocystis jiroveci – pneumonia in AIDS
– Ringworm, thrush, athlete’s foot, and nail fungus
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