Download Colonization of Land By Plants and Fungi

The Colonization of
Land by Plants and
Fungi
Fossil Evidence
• Suggests that plants colonized land in partnership with fungi
• Plants may have colonized land more than 470 million years ago
from Algal ancestors.
• Plants have in common with algae: multicellular, eukaryotic, photosynthetic
• Plants cell walls made of cellulose, like green algae, dinoflagellates and brown algae
• Closest living relative to plants are Charophytes
Charophytes
Charophytes
• Lack Alteration of generations and multicellular, dependent embryos.
• Live by waters edges of ponds and lakes, subject to occasional drying
• Natural selection may have favored those algae that could survive dry
periods, enabling a move to land
Derived traits of plants
• Alternation of generations – life cycle alternates between gametophyte (n)
and sporophyte (2n) organisms. (p506)
• Walled spores produced in sporangia (multicellular organs that produce
spores)
• Apical meristem – localized regions of cell division at the tips of roots and
shoots
• Additional traits that aided to terrestrial life
• Cuticle
• Stomata
Fungi played essential role in colonization of
land plants
• Mycorrhizae – fungi provided essential minerals and nutrients to the early
rootless plants and plants provided food to fungi.
Fungi
• Heterotrophic – absorbs nutrients from the environment outside of its body
• Saprotrophic – release digestive enzymes to break down food and absorb it
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Chitin in cell walls – polysaccharide
Hyphae – tiny filaments, mass of hyphae – mycelium
Asexual and sexual reproduction – through production of spores
Molecular data shows that fungi and animals are more closely related to each other
than plants.
Evolution of Fungi
• Fungi may have colonized land before plants, forming symbiotic
relationships (goes back 405 mya)
• Fungus still being studied today and moved within classification system
based on molecular dating
Fungi play key role in nutrient cycling,
ecological interactions and human welfare
• Decomposers of organic material, breaking down cellulose and lignin
• Symbiotic relationships
• Mycorrhizae – plant roots
• lichens (with algae), seen as a pioneer species
• 30% of fungi species are parasites, most plant pathogens (dutch elm, chestnut
blight, rust, ergot) or animals (ringworm, athlete’s foot)
• Yeasts – unicellular, used in research with Parkinson’s and Huntingtons disease
Plant Kingdom
• 280,000 species
• Ecological, industrial and medical importance
• Thought to evolve from green algae, 500 mya
• Both have chlorophyll a and b, store excess carbs, cellulose in cell walls.
4 Evolutionary Milestones
• Nonvascular/Seedless plants that nourish a multicellular embryo
within the body of the female plant (different from green algae)
• Vascular tissue specialized for transport (430 mya)
• Production of seeds (contains embryo and stored nutrients within
a protective coat) 400mya
• Flower –reproductive structure 135 mya
Cladogram
Traits revisited
• Alternation of Generations: p515
• Gametophyte (n), dominant in nonvascular seedless plants
• sporophyte (2n), dominant in vascular seedless, gymnosperms and angiosperms
• Spores – haploid reproductive cell
• Adaptation to terrestrial life: vascular system, cuticle and stomata
Nonvascular seedless plants
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No means of transporting water or organic nutrients
No true roots, stems or leaves, just root like…
Bryophyte – term for nonvascular plants
Gametophyte is dominant generation, the part of the plant we see.
Characteristics limits size of bryophytes
3 phyla, hornworts, liverworts, and mosses
Vascular plants
• Xylem – conducts water and minerals up from the roots
• Walls of cells are strengthened by lignin
• Phloem – conducts sucrose and other organic compounds down from point
of photosynthesis
• Sporophyte dominant
• Water dependent for reproduction
• Club mosses, ferns and horsetails
Seed plants – Gymnosperms and Angiosperms
• Gymnosperms (naked seed) and angiosperms (flowering plants)
• Contain sporophyte embryo and stored food within a protective seed coat
• Allows survival during harsh conditions
• Heterosporous, 2 types of gametophytes (m/f)
• Pollen grains – male gametophyte
• Pollination – when pollen grain is brought to vicinity of female gametophyte by
wind/pollinator, no water needed!
• Female gametophyte develops within an ovule which eventually becomes a seed
Gymnosperms
• Conifers, cycads, ginkgoes and gnetophytes
• Ovules and seeds are exposed, not enclosed by fruit (naked seed)
Angiosperms
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Flowering plants
Provide clothing, food, medicines
Ovules are enclosed within diploid tissues, fruits are ovaries
Dominance of angiosperms is related to evolution of flying insects
(pollination)
Diversification of flowers
• Wind pollinated – usually bland
• Insect/bird pollinated – usually colorful
• Night blooming flowers – aromatic and white
• Fruits protect and aid in dispersal of seeds