PHYSIO

• Pioneers


  • Ruth Sager
  • Lawrence Bogorad
  • Jean-David Rochaix
• Ruth Sager


  • Discovered chloroplast genetics (Chlamydomonas) and DNA
• Lawrence Bogorad


  Chloroplast genes in

  corn; demonstrated

  light regulation
• Jean-David Rochaix


  Chloroplast gene

  function; nuclear

  control
• Chloroplast Structure

  • Double-membrane envelope
  • Stroma: large soluble interior
  • Thylakoid membrane system
  • Intrathylakoid space or lumen
• Isolated Spinach chloroplast


  • Envelope
  • Stroma
  • Thylakoid membrane
• Stroma of Avena (rye) plastid at high magnification

  • Ribosomes
• Chloroplast Functions


  • Photosynthesis
  • Starch synthesis
  • Fatty acid synthesis
  • Amino acids synthesis
  • Pigment synthesis
  • Nucleotide synthesis
  • Nucleic acids and protein synthesis
  • Sulfur and nitrogen assimilation

  
• Chloroplasts have their own genetic system
• Many of the biosynthetic pathways are regulated, to peak during the light period of L-D cycle
• A similar result was obtained for carotenoids and other chloroplast lipids
• Chloroplast Reproduction


  • All plant and eukaryotic algal cells have plastids
  • Chloroplasts form by division; semi-autonomous
  • Involves proteins (Fts) similar to those that mediate cell division in bacteria

  
• Forms of Plastids


  • Proplastids - precursor of all plastids, found in meristems
  • Etioplasts - form in shoots of dark-grown plants, distinctive internal structure
  • Chloroplasts - in all green tissues
  • Amyloplasts - prominent in roots, store starch, colorless
  • Chromoplasts - in mature fruit, lots of carotenoids, little chlorophyll

  
• Amyloplasts from Glycine (soybean) root-cap (peripheral cell)


  • Starch grains
  • Thylakoid membranes
• Young chromoplast from developing tomato fruit

  • Lycopene crystals
  • Plastoglobuli

  
• Plastid development is plastic & mostly under nuclear control
• Plastid development in shoots

  • Light
  • Proplastids
  • Etioplasts
  • Chloroplasts
  • Chromoplasts

  
• Plastid development in roots

  • Proplastids
  • Amyloplasts
• Chloroplast Genetics


  • Inheritance is typically uniparental, usually maternal
  • Essentially all plastids have DNA, usually the same DNA throughout the organism (homoplasmy)
  • The DNA sequence does not change during differentiation
• There are exceptions to the last 2 statements
• Acetabularia – green alga, fossils known, many species likely extinct


  • A single giant cell (5 cm), 1 nucleus, ~1 x 10^6 chloroplasts
  • ~30 % of chloroplasts don't have DNA!
• Chloroplast DNA (cpDNA) General features


  • Double-stranded, circular molecule
  • No histones, but have bound proteins (e.g., Hu), organized into nucleoids
  • G-C content typically less than nuclear DNA
  • Multiple copies (~30-100) per plastid (i.e., all cp genes are multi-copy)
  • Can be 10-20% of the total DNA in leaves
• DO NOW 20 min
• Terms to define


  • ATP
  • Autotroph
  • Heterotroph
  • Photosynthesis
  • Cellular respiration
• Photosynthesis overview
• Photosynthesis overview


  • Purpose
  • Location
• The light vs. the "dark" reaction
• Chloroplasts pigments


  • Light absorption
  • Types
• Light reactions


  • Photosystems
  • Photophosphorylation
• The light independent reaction ("dark" reaction)

  • Carbon "fixation"
  • Reduction
  • Regeneration
• Alternative plants


  • Mosses, ferns, and flowering plants
  • Kelp
  • Euglena
  • Cyanobacteria
• Almost all plants are photosynthetic autotrophs, as are some bacteria and protists
• Autotrophs

  Generate their own organic matter through photosynthesis
• Sunlight energy is transformed to energy stored in the form of chemical bonds
• Energy can be transformed from one form to another
• Free energy


  Available for work
• Heat


  Not available for work
• The sun is the main source of energy for life on earth
• Different wavelengths of visible light are seen by the human eye as different colors
• Why are plants green?