Transport in Plants

I. Overview

II. Absorption of water in Roots

III. Transport of xylem sap

IV.Control of transpiration

V. Transport of phloem sap

I. OverviewTransport of solutes into the root

•Helps to create water movement•Solutes= # of molecules•osmosis

Differences in water potential

• Three components• Total water potential (ψw)• Pressure potential (positive/negative) ψp

• Solute potential (ψs)

Ψw = ψp + ψs

•Units are MPa

Water potential and movement

•Osmotic movement of water•aquaporins

Absorption of water in Roots

•Symplast = living tissue•Apoplast = cell wall space

Transport of xylem sap•Properties of water•Adhesion•Cohesion•Tension

• Root Pressure

Ascent of Sap

• Transpiration-Cohesion-Tension Theory

• Solar driven• Water potential of air• Relative humidity

Control of transpiration

• Guard cells• Photosynthesis-

transpiration compromise

Mechanism of guard cell opening

Environmental control and adaptations

• Light (Blue light/Red light)

• Water (drought)

• Carbon dioxide (concentration in leaf/around leaf)

Adaptations

• Xerophytes• CAM plants• Leaf hairs• Sunken stomata

Xerophytic Adaptations

Transport of phloem sap

• Source (photosynthetic tissue• Sink (new leaves, seeds, roots• Bidirectional flow• Phloem• Requires energy• Transport of sugars (sucrose), amino

acids, potassium, and hormones

Munch Pressure Flow Hypothesis