lecture 10

• Macronutrients


  C, H, O - fixed as sugars by photosynthesis (H2O+CO2)

  P, K, N, S, Ca, Mg - all come from the soil (1-4% dry weight)
• Micronutrients


  Required in small amounts, mostly as enzymatic co-factors

  Too much can be a bad thing

  Cl, Cu, Fe, Mn, Zn, Mo, B, Ni
• If your houseplant is looking poorly, it may need more nutrients
• How water and minerals get from the soil into the vasculature


  • Travel through the symplast (cytosol connected by plasmodesmata)

  Travel through the apoplast (cell walls and intercellular spaces)

  Substances can pass between symplast and apoplast via the plasma membrane (transmembrane route)
• How other substances (or too much of certain nutrients) are kept from entering the vasculature

  • Water and substances moving by the symplast can pass by plasmodesmata through the endodermis to the vasculature

  Water and substances moving by the apoplast get blocked from entering the vasculature at the endodermis cell wall by the Casparian strip (waxy layer)
• Substances in the apoplast still can get into the cytosol of endodermal cells via the transmembrane route
• The Casparian strip minimizes leakage of accumulated solutes out of the vasculature
• Impacts of the root-soil interface


  • Evolution/Ecology: Plants often locally adapt to difficult soil conditions

  Agriculture: Soil quality decreases when crops are poorly managed, requiring more fertilizer

  Health: We (and other animals) obtain many nutrients from plants, which may also take up toxic minerals

  Environment: Phytoremediation / Phytomining

  Intersection with climate change: As CO2 increases, plants fix more carbon but don't take up proportional amounts of nutrients, leading to poorer food quality
• Shoot apical meristem (SAM)


  Organ primordia form on the margins, producing leaf primordia and axillary buds with their own apical meristems
• If the shoot apex is removed, growth proceeds from the apical meristems of axillary buds
• Phyllotaxy


  The non-random order and arrangement of organ primordia initiation, often in a spiral pattern to avoid self-shading
• Basic leaf types


  • Simple

  Compound

  Tendrils

  Storage leaves

  Spines

  Reproductive leaves
• Leaf anatomy


  • Dermal tissue: upper and lower epidermis with waxy cuticle and stomatal pores

  Ground tissue: palisade and spongy mesophyll

  Vascular tissue: xylem and phloem
• Phyllotaxy


  The non-random order and arrangement of primordia initiation
• In the form of phyllotaxy shown here (spiral), each successive leaf emerges ~137.5º from the site of the previous one
• Phyllotaxy


  • Averts self-shading, also maximizing leaf coverage of ground area + shading shorter competitors
• Basic Leaf Types


  • simple
  • compound
  • tendrils
  • storage leaves
  • spines
  • reproductive leaves
• Dermal Tissue


  • Upper and lower epidermis are lawns of pavement cells coated in waxy cuticle that prevents water loss
  • Stomatal pores (stomata) opened and closed for gas exchange by guard cells (CO2 in, H2O and O2 out)
• Vascular Tissue


  • Xylem and phloem networked throughout in veins
  • Xylem brings water to photosynthetic cells
  • Phloem carries photosynthate back to rest of plant
  • Monocots and dicots differ in venation pattern
• Mesophyll


  • Palisade mesophyll consists of elongated chloroplast-rich cells specialized for light capture
  • Spongy mesophyll form a porous space with high surface area : volume ratio that allows for gas circulation
  • Stomata are only on the lower epidermis to facilitate gas exchange with spongy mesophyll
• Bundle sheath cells


  Surround veins and regulate transfer of substances between mesophyll and vasculature
• Leaf Diversity


  • succulent leaves
  • tendrils
  • storage leaves
  • spines
  • reproductive leaves
• Vascular bundles


  • In monocots they are dispersed throughout, while in eudicots they form a large ring
  • Phloem is peripheral to the xylem
• Secondary Growth


  1. Vascular cambium forms cylindrical bands that add more xylem and phloem

  2. Cork cambium forms a tough, thick, waxy covering called cork that protects stem
• Secondary growth drives the thickening of plant stems (or roots) and mostly occurs only in eudicots and conifers, not in monocots
• Key Terms


  • macronutrient
  • micronutrient
  • apoplast(ic route)
  • symplast(ic route)
  • transmembrane route
  • plasma membrane
  • plasmodesmata
  • Casparian strip
  • suberin
  • phyllotaxy
  • simple / compound leaves
  • rhizomes / stolons / root tubers
  • spines / thorns / prickles
  • secondary growth
  • vascular cambium
  • cork cambium
  • secondary xylem / phloem
  • cork / bark