Multicellular Photosynthetic Autotrophs

Plants

• Multicellular
• Cellulose cell walls
• Chlorophylls a and b
• Develop from embryophyte
• Alternation of generations
• Major food source for terrestrial life
• Atmospheric O2 and CO2 balance
• Coal deposits
• Intimate association with mycorrhizal fungi
• >250,000 species (~500,000?)
• Taxonomy
  • State of flux
• DNA sequencing
• Developmental studies
  • Division (old literature) = phylum (new literature)
  • ~12 phyla, 9 of which are vascular plants

Plant phyla

Phyla are 12 groupings

Plant evolution

• Evolved from green algae, likely related to charophytes
• Evidence
  • DNA sequences
  • homologous chloroplasts: chlorophyll b and beta-carotene; thylakoids in grana;
  • Cellulose in both groups; also peroxisomes
  • Mitosis and cytokinesis similar
  • Sperm ultrastructure

Plant phylogeny

Plant life cycles

• Alternation of generations
• Sporophyte
  • diploid
  • produces spores in sporangia
• Gametophyte
  • develops from spore
  • haploid
  • produces gametes in gametangia
• Haplodiplontic life cycle

Moss life cycle

Vascular plants

• Most have roots
• Aerial shoot systems
• Vascular tissue
  • xylem: water, mineral transport
  • phloem: food transport
• Lignin
• Branched sporophyte is dominant stage
  • amplified production of spores
  • evolution of complex plant bodies
• Dominated Carboniferous (360 my)

Vascular plant life cycles

• Homosporous (single type of spore)
• Heterosporous (two types of spore)

Pterophyta (ferns)

• Non-seed plant
• Sporophyte conspicuous (vascular tissue)
• Rhizome: ground stem, roots
• Fronds: leaves
• Sori: clusters of sporangia
• Motile sperm require external water for fertilization
• Originated in Devonian, 350 my

Tree fern Fern life cycle

Non-seed plants, continued

• Lycophyta: club mosses
  • E.g., Lycopodium (“ground pine”)
  • Many species became extinct 270 my, once dominant (coal formations)
  • Gametophyte non-photosynthetic, nourished by fungi
• Arthrophyta: horsetails
  • Equisitum
  • Some fossil forms (300 my) were tree-size (coal)
  • Photosynthetic stems, no leaves
  • Silica deposits in epidermal cells

Seed plants

• 1st appeared in Devonian, 360 my
• Seed develops from ovule, protects embryo
  • withstands drought
  • dispersal is enhanced
  • no immediate need for water for germination
• Heterosporous
  • male gametophyte: arise from microspores
  • female gametophyte: arise from megaspores in ovule in ovary
• Two groups
  • gymnosperms
  • angiosperms

plant

Sporophyte/gametophyte

Megasporangium (nucellus)

• Key to seed development
• Nucellus: solid, fleshy, surrounded by integuments derived from sporophyte (seed coat)
• Entire structure called ovule
• Flower may have many ovules

Pollen

• Develop from microspores, become male gametophyte
• Protected by sporopellenin
• In most plants, sperm lack flagella (loss)
• Many mechanisms to transport pollen
  • wind
  • insects, birds,

Gymnosperms

• “naked seed”
  • ovule not fully enclosed by sporophyte at time of pollination
• Conifers, cycads, gnetophytes, Ginkgo
• Small, inconspicuous plants to giants like sequoia
• Conifers: to carry cones fv
  • male cones, Female conesvv
  • evergreen

Pine life cycle

Other Coniferophyta

• Cycadophyta: cycads
  • tropical, subtropical
  • flagellated sperm
• Gnetophyta
  • e.g., Ephedra, Mormon Tea
• Ginkgophyta: Ginkgo
  • only one surviving species
  • diocious (separate % and &trees)

Other gymnosperms

Angiosperms

• Flowering plants, Anthophyta
  • monocots- single seed leaf (grasses, lilies, etc.)
  • dicots- two seed leaves (roses, pulses, maples)
• More specialized xylem (water transport)
  • vessel elements
  • fiber cells
• Fossils date to 130 my
• Animal (e.g., insect) coevolution

Earliest angiosperm

• What is earliest angiosperm?
• Recent analysis of nucleotide and amino acid sequences suggests that Amborella, a tropical plant found only on the island of New Caledonia, is closest relative to flowering plants

Angiosperm flower

Angiosperm life cycle

This text is based on notes very generously donated by Paul Doerder, Ph.D., of the Cleveland State University.