1. Plant Mineral Nutrition: Solute Transport HORT 301 – Plant Physiology September 22, 2010 Taiz and Zeiger - Chapter 6, Appendix 1 paul.m.hasegawa.1@purdue.edu Integral membrane transport proteins – responsible for movement of ions across membranes

2. Molecular diffusion - net movement of mineral nutrients and other molecules down the chemical potential gradient, passive transport K + > in B right and Cl - > in left, electrical gradient K + and Cl - move across membrane, concentration gradient No net ion movement across membrane

3. Chemical potential gradient (  ) – forces that drive diffusion Mineral ions and charged molecules – concentration and electrical potential gradients Neutral molecules – concentration gradient, unaffected by charge

4. APOPLAST pH 5.5 CYTOSOL pH 7.2 ΔE=-100 to -200 mV PLASMA MEMBRANE Membrane potential gradient (  E) – electrical potential gradient Differential ion accumulation on sides of the membrane Inside negative membrane potential across the plasma membrane Antiporter

5. APOPLAST pH 5.5 CYTOSOL pH 7.2 ΔE=-100 to -200 mV PLASMA MEMBRANE pH gradient - primarily responsible for the plasma membrane potential gradient pH gradient requires energy Chemical energy (ATP hydrolysis) is coupled to H + -transport against the electrochemical gradient ADP + P i ATP ADP + P i H+H+ H + pumps H+H+

6. APOPLAST pH 5.5 Ion and solute transport across the plasma membrane coupled to ∆pH

7. Translation of a membrane potential gradient into a force for diffusion ∆E can drive diffusion of ions At equilibrium – ion concentration gradient is balanced by the voltage difference ∆E (electrical potential/membrane potential) = 2.3RT/zF log C o /C i At equilibrium 2.3RT/zF = 59 mV, monovalent ion ∆E = 59 mV log C o /C i if C o /C i = 10, log 10 = 1 then ∆E = 59 mV x 1 An inside negative, membrane potential of -59 mV (~60 mV) can translate into a 10-fold concentration difference (monovalent cation)

8. Plasma membrane potential effects on a monovalent anion (e.g. Cl - ), a membrane potential of -120 mV (inside negative) requires that [Cl - ] apoplast must be >100X relative to [Cl - ] cytosol for passive transport Each ion has its own electrochemical potential Specificity is due to unique concentration activity Divalent (Ca 2+ or SO 4 2- ) ions have 2X the electrical potential

9. pH 5.5 pH 7.2 - 100/ -200 mV pH 5.5 +30 mV Passive and active ion transport across the plasma membrane and tonoplast Dependent on concentration and membrane potential gradient Intracellular distribution of essential elements due to passive (dashed, -----) or active (solid line, →) transport

10. Transport protein categories – channels, carriers and pumps

11. Channels – diffusion inwards or outwards across the membrane K + channel

12. Primary active transport – energy production is coupled to ion transport H + electrochemical gradients across the plasma membrane and tonoplast Smith et al. (2010) Plant Biology (pH 5.2) -100 to -200 mV Apoplast Cytosol Vacuolar H + -ATPase ADP + P i ATP H+H+ PM H + -ATPase

13. Secondary active transporters (carriers) – couple H + transport to ion transport Down the H + electrochemical gradient Symporter – same direction, antiporter – opposite directions

14. Model of H + -sucrose symporter function

15. Raven et al. (2005) Biology of Plants H + -ATPase and H + -sucrose symporter coordination

16. Transport proteins at the plasma membrane Smith et al. (2010) Plant Biology pH 7.4 -100 to -200 mV pH 5.5

17. Tonoplast transport proteins Smith et al. (2010) Plant Biology pH 7.2

18. +30 mV

19. Radial ion transport from soil solution to the xylem