Kitajima%20week20 - BSC 2011 Kitajima Week 2 Chapter 36 -...

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BSC 2011 Kitajima Week 2 22 Chapter 36 - Transport in vascular plants 1. Plant water relation: water potential and ascent of sap in xylem 2. Selective uptake of mineral nutrients in roots 3. Sugar transport in phloem Minerals H 2 O CO 2 O 2 CO 2 O 2 H 2 O Sugar Light How plants capture resources above and below ground, and transport them to where they are needed. Sugar is necessary for maintenance respiration, growth and symbiotic microbes. Water is necessary for photosynthesis, to keep leaves cool, and to maintain long-distance transport via Minerals are necessary for synthesis of amino acids, proteins, DNA, coenzymes, chlorophylls. Overview • Concept: Physical forces drive the transport of materials in plants over a range of distances • Transport in vascular plants occurs on three scales – Transport of water and solutes by individual cells, such as root hairs – Short-distance transport of substances from cell to cell at the levels of tissues and organs – Long-distance transport within xylem and phloem at the level of the whole plant
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BSC 2011 Kitajima Week 2 23 Minerals H 2 O CO 2 O 2 CO 2 O 2 H 2 O Sugar Light Ascent of sap through xylem Figure 36.2 (Read captions in the book) Translocation of organic compounds via phloem Lecture 4: water transport and ascent of sap • Water potential • SPAC (soil-plant-atmosphere continuum) and ascent of sap • Stomata and transpiration Water potential is expressed in the unit of pressure. • MPa (megapascal) = 10 bar = about x10 atmospheric pressure. • Water in a closed syringe under compressive force has a positive water potential. • Salt water in an open container has a negative water potential.
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BSC 2011 Kitajima Week 2 24 Water potential = zero for water in open container at the ground level. • Solute potential = concentration of water molecules (always negative) • Pressure potential = effects of pressure for water in enclosed space (+ or – in xylem) • Matrix potential = adehesion of water to slightly charged surface by hydrogen bond (always negative - found at sufvace of soil particles and cell wall - very important in consideration of evaporation from surface of leaf mesophyll cells) • Gravity potential matters only for tall trees (+). Matrix potential and capillary rise Solute potential generated by semi- permeable membrane Figure 36.5a 0.1 M solution H 2 O Pure water ψ P = 0 ψ S = 0.23 ψ = 0.23 MPa ψ = 0 MPa (a) Before water starts to move (= before water column heights become different) After water rises, water height difference generates positive pressure potential to equilibrates (0 Mpa for both sides).
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BSC 2011 Kitajima Week 2 25 Application of physical pressure Increases water potential H 2 O ψ P = 0.23 ψ S = 0.23 ψ = 0 MPa ψ = 0 MPa (b) H 2 O ψ P = 0.30 ψ S = 0.23 ψ = 0.07 MPa ψ = 0 MPa (c) Figure 36.5b, c Before water starts to move (= before water column heights become different) When plant cells have lower solute potential than
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Kitajima%20week20 - BSC 2011 Kitajima Week 2 Chapter 36 -...

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