1. Plant Mineral Nutrition: Solute Transport HORT 301 – Plant Physiology October 9, 2009 Taiz and Zeiger, Chapter 6, Web Chapter 2 (p 1-10), Web Topic 6.3 paul.m.hasegawa.1@purdue.edu Mineral nutrient and solute movement (transport) across the lipid bilayer of membranes Integral membrane transport proteins

2. Net transport of molecules from high to low concentration (diffusion)

3. Chemical potential (  ) drives solute transport across membranes Concentration gradient and electrical potential Passive Active

4. Existence of a membrane potential (  E) indicates that ions accumulated differentially on sides of the membrane APOPLAST pH 5.5

5. Transformation of an electrical gradient (membrane potential) into a concentration gradient ∆E (electrical potential/membrane potential) = 2.3RT/zF log C o /C i At equilibrium 2.3RT/zF = 59 mV ∆E = 59 mV log C o /C i if C o /C i = 10, log 10 = 1 then ∆E = 59 mV x 1 Thus, a membrane potential of ~60 mV = 10-fold concentration difference

6. For a univalent anion (-, e.g. Cl - ), a membrane potential of -120 mV (inside negative) requires that [Cl - ] apoplast must be >100X relative to Cl - symplast for passive transport Divalent (Ca 2+ or SO 4 2- ) ions have 2X the electrical potential Each ion has its own electrochemical potential K + and Cl - each diffuse to net chemical steady-state Specificity is due to unique concentration activity

7. Proton (H + ) electrochemical gradient - generates membrane potential (electrical gradient) and pH (H + ) gradients Facilitate passive and secondary active transport of ions and solutes H + pumps

8. ATP and PPi – energy sources for generating H + electrochemical gradients across the plasma membrane and tonoplast Smith et al. (2009) Plant Biology

9. pH 5.5 pH 7.2 - 100/ -200 mV pH 5.5 +30 mV Intracellular distribution of essential elements due to active (solid line) or passive (dashed) transport

10. Transport Proteins – individual proteins or multi-subunit complexes (quaternary structure) Plasma membrane H + -ATPaseVacuolar H + -ATPase

11. Transport protein categories – channels, carriers and pumps

12. Raven et al. (2005) Biology of Plants Secondary active transport - symporter

13. Symporter and antiporter – secondary active transporters

14. Transport proteins at the plasma membrane Smith et al. (2009) Plant Biology

15. Tonoplast transport proteins