Transport in Vascular Plants and Nutrition

Capillary action

• Thinner tube = greater height

• Tracheids and Vessel elements

Transpiration

• Tensile strength of water column

• Water potential

• Evaporation

• Water is cohesive and adhesive

• Minerals

Cohesive

• Water sticks to itself

Adhesive

• Water can stick fast to a surface or object

Root pressure

• Water enters via osmosis

Apoplastic route

• Water and solutes move through the cell wall

Symplastic route

• Water and solutes move through the cytosol (no cell wall)

Transmembrane route

• Water and solutes move through the cell wall and plasma membrane

Osmosis

• The diffusion of water into or out of a cell that is affected by solute concentration and pressure

Water potential

• A measurement that combines the effects of solute concentration and pressure

  • Determines the direction of movement of water

  • “Potential” refers to water’s capacity to perform work

• 0 is high — e.g. soil

• -100 is low — e.g. armosphere

• Water moves from high to low

Turgid

• A plant has turgor pressure allowing it to be erect

• Flaccid is placed in lower solute concentration

Flaccid

• Turgor loss occurs — causes wilting

• Can be reversed once plant is watered

Stomatal Opening and Closing

• Changes in turgor pressure

  • When turgid, guard cells bow outward and the pore between them opens

  • When flaccid, guard cells become less bowed and the pore closes

Bulk flow

• Movement of liquid by driven pressure

  • Efficient long-distance transport of fluid

• Absorption occurs near root tips where root hair is located and the epidermis is permeable to water

• Water and solutes move together through tracheids and vessel elements of xylem and sieve-tube elements of phloem

  • Mature tracheids and vessel elements have no cytoplasm

  • Sieve-tube elements have few organelles

Endodermis

• The innermost layer of cells in the root cortex

• Surrounds vascular cylinder

• Last checkpoint for selective passage of minerals from the cortex into the vascular tissue

• Water can cross cortex via symplast or apoplast

• Water and minerals in the apoplast must cross the plasma membrane of an endodermal cell to enter the vascular cylinder

• Regulates and transports needed materials from the soil to the xylem

• Water and minerals move from protoplasts of endodermal walls into their cell walls

Caspian Strip

• Waxy, suberin coated part on the endodermal wall

• Blocks apoplastic transfer of minerals from the cortex to the vascular cylinder

Diffusion and Active transport in plants

• Involved with the movement of water and minerals from the symplast to apoplast

• Water and minerals now enter tracheids and vessel

Transpiration

• Transport of xylem sap

• The evaporation of water from a plant’s surface

• Water is replaced as it travels up from the roots

• Water vapour in airspaces of a lead diffuse down its water potential gradient and exits leaf via stomata

• The surface tension of water creates a negative pressure potential

  • Pulls water and minerals from the root up

Translocation

• Products of photosynthesis are transported through phloem

• Phloem sap is an aqueous solution that is high in sucrose

• It travels from a sugar source to a sugar sink

• Sugar must be loaded into sieve-tube elements before being exported to sinks

• Sugar can be moved symplastic or both symplastic and apoplastic pathways depending on species

Sugar source

• Where sugars are made — in the chloroplasts of leaves

Sugar source

• Where sugars end up like roots, seeds, tubers

Fertilization

• Replaces mineral nutrients that have been lost from the soil

• Soils are made up of both organic and inorganic materials

• Soils can become depleted of nutrients as plants and the nutrients they contain are harvested

• Enriched in nitrogen, phosphorous, potassium

Macronutrients

• Nine of the essential elements

• Carbon, oxygen, hydrogen, nitrogen, phosphorous, sulphur, potassium, calcium, magnesium

• C,O,H are sugars

• Needed in relatively large amounts

Micronutrients

• Remaining eight essential elements

• Chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum

• Needed in very small amounts

Nitrogen

• Nucleic acids, proteins, and chlorophyll

Potassium

• Cofactor of many enzymes

• Major solute functioning in water balance

• Operation of stomata

Calcium

• Important component of middle lamella and cell walls

• Maintains membrane function

• Signal transduction — cell signalling

Magnesium

• Component of chlorophyll

• Cofactor of many enzymes

Phosphorous

• Component of:

  • Nucleic acids

  • Phospholipids

  • ATP

Sulphur

• Component of proteins

Chlorine

• Required for water-splitting step of photosynthesis

• Functions in water balance

Iron

• Component of cytochromes

• Cofactor of some enzymes

• Cofactor in chlorophyll synthesis

• Needed for photosynthesis

Manganese

• Active in formation of amino acids

• Activates some enzymes

• Required for water-splitting step of photosynthesis

Boron

• Cofactor in chlorophyll synthesis

• May be involved in carbohydrate transport and nucleic acids synthesis

• Role in cell wall function

Zinc

• Active in formation of chlorophyll

• Cofactor of some enzymes

• Needed for DNA transcription

Copper

• Component of many redox and lignin-biosynthetic enzymes

Nickle

• Cofactor for an enzyme function in nitrogen metabolism

Molybdenum

• Essential for mutualistic relationship with nitrogen-fixing bacteria

• Cofactor in nitrate reduction