文档介绍：Part 2 Long-Distance Transport
Overview of diffusive and convective transport in plants
Diffusion and convection are the basis for solute transport.
Diffusion: An independent movement of molecules driven by a concentration gradient.
Convective transport: Bulk flow of solution driven by a pressure gradient.
Water and solutes can move from cell to cell along either of two parallel aqueous pathways.
The concept of water potential provides a thermodynamic basis for the study of water movement.
Equation
ψw=ψp+ψs+ψg+ψm
ψw :water potential
Ψp: pressure potential
ψs: solute (osmotic) potential
ψg: gravitational potential
ψm: matrix potential
Concentration gradients over short distances tend to drive both diffusion and osmotically generated pressure flow (OGPF).
of xylem and phloem transport
Some generalizations and parisons can be
made about position of xylem and phloem exudates.
Xylem and phloem transport streams can be sampled by several methods
Table General characteristics of xylem and phloem exudates
Phloem exudates Xylem exudates
Sugars 100-300gl-1 0gl-1
Amino acids 5-40gl-1 -2gl-1
anics 1-5gl-1 -4gl-1
Total solutes 250-1200mmol kg-1 10-100mmol kg-1
pH - -