Forces moving water through plants I. Movement of water through the soil toward a root:

1. Forces moving water through plants I. Movement of water through the soiltoward a root: - absorption at root surface creates matric effects II. Absorption (movement of water into the root from the soil): 1) movement into the root apoplast - mostly by bulk flow

2. - efficiency of absorption varies over length of root, due to a) presence/absence of root hairs b) presence/absence of suberized cell layers

3. II. Absorption, continued 2) movement from root apoplast into root symplast - mostly by diffusion across cell membranes - occurs mostly in the cortex

4. aquaporins influence rate - allow for diffusion or bulk flow

5. endodermis influences location

6. 3) movement into stele apoplast mostly by diffusion across cell membranes

7. ** the driving force for absorption is a water potential gradient, created by differences in solute concentration - solute concentration in the soil solution - solute concentration in root - in the cortex apoplast - in the stele apoplast active accumulation of mineral ions, role of endodermis

8. III. Transport from roots to shoots through specialized water transport tissue = xylem xylem tissue consists of: tracheids vessel members fibers parenchyma cells

9. tracheids & vessel members: have some similarities; some differences - elongate cells - primary cell walls; lignified secondary cell walls - undergo apoptosis - pits

10. pits may align into pit pairs pit membrane torus

11. vessel members 1) shorter and wider 2) perforation plates in their end walls 3) stack to form vessels tracheids & vessel members provide pathways for bulk flow of water throughout the plant

12. bulk flow through xylem requires a pressure gradient pressureroots > pressureshoots, created by a) increasing pressure at roots b) decreasing pressure at shoots must overcome a) gravity b) frictional drag

13. force needed to move water up through the xylem is ~0.03 MPa/m provided by the pressure gradient between roots and shoots

14. increasing pressure at the roots - can be caused by absorption - root pressure ~ 0.1 MPa under ideal conditions

15. decreasing pressure at shoots hypothetical mechanism = Cohesion Tension mechanism