Evolution and Diversity of Green and Land Plants from ppt

• Green plants


  A monophyletic group of eukaryotic organisms that includes what have traditionally been called green algae plus the land plants or embryophytes
• Green plants


  • Have cells with membrane-bound organelles, including: a nucleus, microtubules, mitochondria, an endoplasmic reticulum, vesicles, golgi bodies
• Cellulosic cell wall


  Cellulose is secreted outside the plasma membrane as microscopic fiber-like units called microfibrils that are further intertwined into larger fibril units, forming a supportive meshwork. Function: to impart rigidity to the cells, acting as a cellular exoskeleton
• The evolution of a cellulosic cell wall was an introduction to the evolution of more complex types of growth, particularly of self-supporting shoot systems
• Green plants


  • Elodea (whole leaf in face view)
  • Chlamydomonas reinhardtii (unicellular green alga)
• Chloroplasts


  • One of the major defining characteristics of traditionally defined plants; their adaptive significance as organelles functioning in photosynthesis and the conversion of light energy to chemical energy
  • Contain chlorophyll b in addition to chlorophyll a, the former of which acts as an accessory pigment in light capture
  • Have thylakoids, the chlorophyll-containing membranes that are stacked into grana, which are pancake-like aggregations
  • Manufacture true starch, a polymer of glucose sugar units (= polysaccharide) as a storage product
• All green plants, from filamentous green algae in a pond or tide pool to giant sequoia or Eucalyptus trees have this same type of chloroplast
• Recent data imply that chloroplasts found in the green plants today were modified from those that evolved via endosymbiosis, the intracellular cohabitation of an independently living, unicellular prokaryote inside a eukaryotic cell
• Chlorophytes


  One of the two sister groups of green plants
• Streptophytes


  The other of the two sister groups of green plants
• Green algae


  A paraphyletic group and are defined as the primarily aquatic Chlorobionta, consisting of all chlorophytes and the non land plant streptophytes
• Green algae


  • Flagellated unicells with or without flagella
  • Thalloid forms
  • Motile and nonmotile colonies
  • Nonmotile filaments
• Green plant sexual reproduction

  Seems to have been the production of flagellate, haploid (n) gametes that are isomorphic, that is look identical. Fertilization occurs by union of two of these gametes, resulting in a diploid (2n) zygote
• Haplontic life cycle


  The zygote, which is free-living, then divides by meiosis to form four haploid spores, each of which may germinate and develop into a new haploid individual, which produces more gametes, completing what is termed a haplontic (or haplobiontic) life cycle
• Oogamy


  A type of sexual reproduction in which one gamete, the egg, becomes larger and nonflagellate; the other gamete is, by default, called a sperm cell
• Oogamy is found in all land plants and independently evolved in many other groups, including many other algae and in the animals
• Retention of the egg and zygote

  Retention of the egg and retention of the zygote on the parent body was adaptive, by making possible the future nutritional dependence of the zygote upon the haploid plant, ultimately leading to the sporophyte
• Charophytes


  A clade within the streptophytes that includes the Coleochaete, Charales, and the land plants, are plasmodesmata
• Charophytes


  • Coleochaete sp.
  • Nitella sp.
  • Chara sp.
• Plasmodesmata


  Essentially pores in the primary (1°) cell wall through which membranes traverse between cells, allowing for transfer of compounds between cells. Function: more efficient or rapid transport of solutes, including regulatory and growth-mediating compounds, such as hormones
• Charales, such as the genera Chara and Nitella, are perhaps the closest living relatives to the land plants
• Charales


  • Form whorls of lateral branches and grow by means of a single apical cell, resembling that of some land plants (but differing in lacking true parenchyma)
  • Have specialized male and female gametangia, termed antheridia and oogonia
  • Oogonia have a spirally arranged group of outer cells
• Oogonia and antheridia of the Charales resemble the archegonia and antheridia of land plants in having an outer layer of protective cells, but have been thought not to be directly homologous because of differences in structure
• The first colonization of plants on land during the Silurian period, was connected with the evolution of several important features. These shared, evolutionary novelties constituted major adaptations that enabled formerly aquatic green plants to survive and reproduce in the absence of a surrounding water medium
• Sporophyte


  A key evolutionary novelty that enabled the first colonization of land plants
• Oogonia


  Female reproductive structures
• Antheridia


  Male reproductive structures
• Oogonia and antheridia of the Charales


  Resemble the archegonia and antheridia of land plants
• Oogonia and antheridia of the Charales have an outer layer of protective cells, but have been thought not to be directly homologous because of differences in structure
• Charophytes


  A clade within the streptophytes that includes the Coleochaete, Charales, and the land plants
• Charophytes are plasmodesmata
• The first colonization of plants on land during the Silurian period, was connected with the evolution of several important features
• Shared, evolutionary novelties that constituted major adaptations enabling formerly aquatic green plants to survive and reproduce in the absence of a surrounding water medium

  • Evolution of the embryo and sporophyte
  • Evolution of cutin and cuticle
  • Evolution of parenchyma tissue
  • Evolution of antherium
  • Evolution of archegonium
• Sporophyte


  A separate diploid (2n) phase in the life cycle of all land plants
• Gametophyte


  The corresponding haploid, gamete-producing part of the life cycle
• Haplodiplontic alternation of generations

  Having both a haploid gametophyte and a diploid sporophyte, commonly called alternation of generations
• Sporophyte development


  1. Zygote undergoes mitotic divisions, resulting in the formation of a separate entity called the sporophyte

  2. Differentiation of the embryo, an immature sporophyte attached to or surrounded by the gametophyte
• In many land plants, such as seed plants, the embryo remains dormant until specific environmental conditions are met
• Sporangium development


  1. Portion of the sporophyte differentiates into the spore-producing region, the sporangium

  2. Sporogenous tissue matures into sporocytes, which undergo meiosis to produce haploid spores

  3. Spores are essential for reproduction and dispersal
• Sporangial wall


  • Envelops the sporangium, composed of one or more layers of sterile, non-spore-producing cells
  • Provides protection to the developing spores and aids in their dispersal