Plant Diversity, Seed Evolution, and Fungi

• Study notes for Plant Diversity, Evolution of Seed Plants, and Fungi

Key Terms and Concepts

• Derived traits, the 4 traits that make a plant a plant
• Gametophyte/sporphyte - Antheridium/Archegonium
• Seedless vascular plants and seedless nonvascular plants
• Alternation of generations involves meiosis and fertilization
• Nonvascular plants, seedless vascular plants, angiosperms, and gymnosperms are plant types
• Pollination is the process of transferring pollen
• Gymnosperms are naked seed plants
• Angiosperms seeds are found in fruits
• Budding, mycorrhizae, hyphae, plasmogamy, and karyogamy are terms needed to be understood

Plant Colonization and Evolution

• Green algae, charophytes within Archaeplastida, are land plants closest relatives
• Earth is about 4.5 billion years old
• Cyanobacteria and protists existed on land 1.2 billion years ago
• Small plants, fungi, and animals emerged on land around 500 million years ago
• Plants are the ultimate source of most food for land animals, and also provides oxygen
• Vascular plants arose at least 475 million years ago
• 96% of known species are vascular plants as opposed to bryophytes
• The 4 key traits for plants are:
  • Alternation of generations
  • Walled spores produced in sporangia
  • Multicellular gametangia
  • Apical meristems
• Apical meristems are localized growth/cell division regions at tips of roots and shoots

Alternation of Generations

• Adult plants alternate between multicellular stages, called alternation of generations
• Gametophytes are haploid and produce haploid gametes via mitosis
• Fusion of gametes creates a diploid sporophyte
• Sporophytes produce haploid spores via meiosis
• Spores grow into gametophytes and produce gametes
• Two gametes create a diploid zygote, growing via mitosis into a sporophyte
• Meiosis generates haploid spores completing the cycle
• Sporophytes produce spores in sporangia
• Spores are haploid, created when diploid sporocytes (2n) undergo meiosis
• These spores develop into gametophytes via mitosis
• Gametes are produce in gametangia
• Archegonia produce eggs and are the site of fertilization, singular form is archegonium
• Antheridia produces and releases sperm, singular form is antheridium

Nonvascular and Seedless Vascular Plants

• Bryophytes are small plants lacking vascular tissue, roots, and true leaves
• The three phyla of bryophytes are liverworts, mosses, and hornworts
• These represent earliest lineages from the ancestor of land plants
• Bryophytes have life cycles dominated by gametophytes
• Seedless vascular plants having flagellated sperm are restricted to moist environments
• The vascular plants make up 96% of known species
• Seedless vascular plants allowed first plants to grow tall
• There are two clades of seedless vascular plants
  • The Lycophytes (phylum Lycophyta) consists of:
    • Club mosses which looks like bigger mosses
    • Have microphylls
  • The Monilophytes (phylum Monilophyta) consist of:
    • Ferns and their relatives which have complex, large megaphylls leaves
• The ancestors of modern lycophytes and monilophytes forming first forests
• Growth and photosynthesis reduced atmospheric CO2 potentially cooling the point and allowed species to move to land
• The decaying plants of ancient forests became coal

Seed Plant Adaptations

• Seed plants originated 360 million years ago
• A seed consists of an embryo and nutrients with a protective coat, and can be dispersed
• Common traits to all seed plants:
  • Reduced gametophytes
  • Heterospory
  • Ovules
  • Pollen
• Seed plants have microscopic gametophytes, getting nutrients from the parent plant
• Early seed plants had homosporous seedless plants but evolved to be heterosporous
• Female gametophytes result from megasporangia producing megaspores
• Male gametophytes result from microsporangia producing microspores

Ovules and Pollen

• An ovule contains a megasporangium, a megaspore, and integuments
• Gymnosperm megasporangia- one integument
• Angiosperm megasporangia- two integuments
• Seed plants retain megasporangium and megaspores in the sporophyte
• The egg develops and is produced from the megaspore within the ovule
• Pollen grains contain the male gametophyte inside the pollen wall
• Pollination is the transfer of pollen to the seed plant part with the ovules
• If germination occurs, the pollen grain creates a pollen tube, discharging two sperm for double fertilization internally
• A seed is from the whole fertilized ovule being the sporophyte embryo with its food supply and protective coat

Seed Advantages and types of Vascular Seed Plants

• Seeds may stay dormant and have a food supply
• They can be transported via external forces
• Gymnosperms refers to naked seeds
• Usually seeds from cones arise from:
  • Cycads- woody, like palms
  • Ginkgo (Ginkgo biloba)
  • Guetophytes
  • Conifers
• Angiosperm seeds are found in fruits derived from mature ovaries

Angiosperm Adaptations and Life Cycle

• Angiosperms are seed plants with reproductive structures called flowers and fruits, being about 90% of species types
• However, this is a very young phylum relatively
• Flowers are angiosperm structure specialized for sexual reproduction
• These can be pollinated via both external and internal sources
• There are up to 4 types of modified leaves called floral organs
  • Sepals enclosing the flower
  • Petals- brightly colored- attracts pollinators
  • Stamens- produces pollen, being male organs:
    • Pollen- MICROspores
    • Stalk (filament) and terminal sac (anther)
  • Carpels- produce ovules- female organ
    • Ovules- MEGAspores
• A carpel includes
  • An ovary, found at the base
  • A style, leading up to a stigma
• After fertilization, an ovary may turn into fruit
• The flower of the sporophyte includes male and female parts
• Male microsporangia within anthers contain the male gametophytes (pollen)
• The embryo sac, a female gametophyte forms within the ovule contained wihtin the stigma which is located in the base of the ovaries

Angiosperm Reproduction

• Flowers are structured for cross-pollination
• After landing, a pollen grain germinates, and the male gametophyte grows down to the ovary
• In double fertilization, the pollen tube releases two sperm into the gametophyte
• One sperm fertilizes the egg, the other combines with two nulcei in the female gametophyte central cell which stimulates growth of the endosperm
• The triploid endosperm nourishes the embryo
• Inside a seed, the embryo has a root and cotyledons (two seed leaves)

Fungi Overview

• The key terms for the fungi portion include budding, mycorrhizae, hyphae, plasmogamy, and karyogamy

Fungi Structures and Nutrition

• Fungi are heterotrophs which feeds via absorption of nutrients
• Fungi have key traits and diverse set of nutrition that they derive from
• Fungi is a monophyletic group of heterotrophs
• They digest then eat
• Fungi exist in diverse lifestyles:
  • Decomposers
  • Parasites
  • Mutualists

Fungal Body Structure and Hyphae

• Common body structure- multicellular filaments with single cells
• These multicellular species are made of tiny filaments with tubular cell walls called hyphae
• They consist of mycelia being an interwoven mat adapted for absorption
• Fungal cell walls have chitin which is flexible
• Fungal hyphae consists of cells divided via septa
• They allow cell-to-cell organelle movement

Mycorrhizae and Fungal Reproduction

• Mycorrhizae refers to mutually beneficial relationships between fungi and plant roots
• Mycorrhizal fungi carry nutrients to plants and are prevalent in vascular plants
• By generating haploid cells (spores), mycorrhizal fungi are able to colonize other soils
• Fungi can propagate themselves through the production of copious spores
• This can occur in both sexual and asexual life cycles
• Asexual reproduction is possible, but if they can also reproduce sexually via finding a partner

Sexual and Asexual Reproduction

• Sexual reproduction provides genetic variation
• The general form of fungal nuclei is haploid
• Sexual reproduction occurs when hyphae from different mating types fuse together
• Pheromones are utilized by fungi as signaling molecules in their mating method
• The pheromones bind receptors and the hyphae bends toward pheremones causing plasmogamy- cytoplasm joining
• Then hours/days/centuries later… karyogamy which is nuclear fusion will occur
• In karyogamy, haploid nuclei fuse, causing diploid cells to form and the "mating"

Fungal Asexual Reproduction and Phylogeny

• Some fungi reproduce asexually
• Molds generate haploid spores by mitosis and generate noticeable mycelia
• Other asexual fungi= yeasts with single cells
• Instead of spore creation, yeasts reproduce asexually through simple cells, "pinching off" i.e. budding from separate parent cells
• UNICELLULAR, FLAGELLATED ANCESTOR is the origin of fungi with animals being more closely related
• OPisthokonts clade is formed by fungi, animals, and protist relatives

Fungal Phyla

• From DNA analysis, fungi evolved from single-celled, flagellated protist- nucleariids
• There are five fungal phyla:
  • Chytrids
  • Zygomycetes
  • Glomeromycetes
  • Ascomycetes (sac fungi)
  • Basidiomycetes
• Basidiomycetes consists of fruiting bodies i.e. mushrooms and toadstools and are important decomposers