1. Skotomorphogenesis Seed germination Genes and enzymes Embryo and Seed development Plant life cycle Photomorphogenesis Photoreceptors Phytochrome Cells and cell growth Phytochrome: regulation of light responses Photosynthesis: light reaction Photosynthesis: carbon fixation Photorespiration Primary & secondary metabolism Respiration Mineral Nutrition Water #7-The Wet Phase: Physiological Properties of Water HORT 301 – Plant Physiology September 8, 2010 Taiz and Zeiger – Chapter 3, Chapter 15 (p. 441-452) paul.m.hasegawa.1@purdue.edu

2. Water (H 2 0) – most abundant and limiting molecule in plants Water - 95% of cell volume 97% of water absorbed by roots is transpired Transpiration – occurs predominantly through stomata Stomatal number and opening/closing are highly regulated

3. Water (H 2 O) – most limiting resource for plants Yield in agriculture and productivity in ecosystems Day time vapor pressure deficits

4. Molecular structure of water – polar molecule without net charge Oxygen has stronger attraction for shared electrons Creates local negative and positive charges

5. Interaction (hydrogen bonding) between water molecules

6. Properties of water Biochemical solvent for polar molecules Temperature buffering and cooling – high specific heat and latent heat of vaporization Cohesion and tensile strength

7. Adhesion and surface tension drive long distance water transport

8. Capillarity – water movement up xylem vessels

10. Properties of Water Water is a polar molecule Hydrogen bonding between molecules High specific heat and latent heat of vaporization High surface tension (negative pressure), cohesive and adhesive properties Physiological Functions Principal component of plant cells Turgor cell volume increase Biochemical solvent Coolant Capillarity and transpiration move water and nutrients from root to shoot

11. Water movement – diffusion/osmosis and bulk flow Diffusion – movement from high to low concentration Raven et al. 2005 Biol of Plants

12. Osmosis – diffusion of water across a membrane Aquaporins - water channels that facilitate diffusion

13. Bulk flow water movement – large quantities Forces include gravity and pressure Raven et al., 2005, Biology of Plants

14. Water movement - water potential (Ψ w ) gradient Higher → lower water concentration (lower → higher solute concentration) Higher → lower Ψ w (more negative)

15. Water potential (Ψ w ) components – Ψ w = Ψ s + Ψ p Ψ w (water potential) Smith et al., (2010) Plant Biology Ψ s (solute (osmotic) potential) – solute concentration effect on Ψ w van’t Hoff equation, Ψ s = -RTc s Ψ p (hydrostatic pressure/pressure potential/turgor pressure)

16. Water potential (Ψ w ) – of a solution – solutes decrease Ψ w (more negative)

17. Water uptake into cells – driven by the water potential (Ψ w ) gradient Water moves from less negative to more negative Ψ w (0.1 M sucrose solution, Ψ w = -0.244 MPa) Ψ w = Ψ s + Ψ p

18. Water movement from the cell – apoplastic water potential becomes more negative than cellular water potential

19. Water movement into and out of cells summary: Water moves from higher (less negative) to lower (more negative) Ψ w Ψ w(apolast) = Ψ w(symplast) No water movement Ψ w(apoplast) higher (less negative) than Ψ w(symplast) (more negative) Turgor pressure increases and water moves into the cell (volume increase/cell expansion) Ψ w(apoplast) lower (more negative) than Ψ w (sympast) Turgor pressure decreases and water moves out of the cell

20. Turgor pressure drives cell expansion Water potential gradient facilitates water uptake and cell volume increase PLANT BIOLOGY, Smith et al. Figure 3-66.

21. Turgor and growth rate Turgor Pressure (MPa) Growth rate is defined by the formula: GR = m(  p –Y)

22. Plant water status affects critical physiological functions – water potential (Ψ w ) is a “signal” for numerous physiological processes