1. Water Movement through Plants HORT 301 – Plant Physiology September 10 and 13, 2010 Taiz and Zeiger, Chapters 4, 18 (p. 524-531), 23 paul.m.hasegawa.1@purdue.edu Driving forces for water movement from soil to plant shoot

2. Soil water holding capacity - soil water availability for uptake by roots Soil type and structure

3. Water movement through soil - pressure-driven bulk flow, ∆Ψ p A A B

4. Soil hydraulic conductivity during dehydration – field capacity and permanent wilting point Taiz and Zeiger 2006

5. Water uptake into roots – lateral roots and root hairs

6. Radial water transport to the xylem - apoplastic, symplastic and transcellular pathways Uptake into root cells - ∆Ψ W Aquaporins facilitate symplastic water uptake into roots

7. Water transport through the xylem – root to shoot, ∆Ψ p gradient Xylem elements

8. Xylem tracheary element interconnections – apical to basal and radial

9. Smith et al. (2010) Plant Biology Xylem element morphology

10. Water movement from roots to leaves – cohesion-tension theory, ∆Ψ p Substomatal cavity – liquid to vapor Extensive vascular system in a leaf

11. Transpiration – plant water loss to the atmosphere ~95% of plant water loss through stomata Water vapor concentration difference along the transpirational pathway drives evaporation

12. Primary forces that drive water movement: 1. Soil – ∆  p that drives bulk flow 2. Uptake by plant root cells – ∆  w facilitates osmosis due mainly to intracellular  s 3. Root to shoot – ∆  p, surface tension in the sub-stomatal cavity 4. Sub-stomatal cavity to atmosphere – Δc wv, vapor concentration gradient 1 2 3 4

13. Cuticle and boundary layers are resistances to leaf transpiration

14. Stomata and transpiration About 95% of plant water loss occurs through stomata Stomatal complex – pore surrounded by a pair of guard cells that control the aperture size

15. Guard cell anatomy Kidney shaped and dumbbell shaped (most grasses) guard cell pairs

16. Guard cell turgor and volume regulate stomatal pore aperture Opening – turgor increase, water uptake and increased cell volume Closing – turgor reduction, water loss and cell volume reduction Smith et al. (2010) Plant Biol

17. Raven et al, 2005 Biology of Plants Cellulose microfibrils and stomatal function

18. Raven et al, 2005 Biology of Plants Cell wall arrangement regulates guard cell function

19. Light, circadian rhythm, CO 2 and drought stress (ABA) regulate stomatal opening/closing

20. mediated stomatal closure mechanism: Water deficit → ABA → stomatal closure ABA → ROS → Ca 2+ ↑ → Cl - efflux/membrane potential depolarization → K + efflux/K + influx is blocked → ψ p decrease/water loss → volume reduction → stomatal closure ABA → NO/S1P → cADP ribose/IP3 → Ca 2+ → pm H + -ATPase inhibited → H + gradient dissipation (pH) → K + efflux ABA causes stomatal closure and inhibits stomatal opening