Transport In Plants – Chapter 36

• I – Surface Area Adaptations

• II – Cell to Cell Transport

• III – Radial (Lateral) Transport

• IV – Bulk Flow (Longitudinal) Transport

•…. we want SA (sah)

I - Root hairs, mycorrhizae, maximize

surface area of roots…..

• “Infected” roots form mycorrhizae, ????

• Why is this good?.

Fig. 36.8

Mycorrhizae…a good relationship

• Adaptation of Root Tip Epidermal Layer

• Recognize analogous structure to villi.

ROOT Hairs

• Transport in plants occurs on three levels:

(1) Cellular transport;the uptake and loss of water and solutes by individual cells

(2) Lateral transport

(3) long-distance, longitudinal transport.

Fig. 36.1

• The selective permeability of a plant cell’s plasma membrane controls the movement of solutes between the cell and the extracellular solution.

• When is it PASSIVE

• When is it ACTIVE.

• Transport proteins enhance selectivity, and active ability.

II - Cellular Transport

• The most important active transporter in the plasma membrane of plant cells is the proton pump.

• Pump hydrogen ions (H+) out of the cell.

• Why is this “good” for plant??

Proton pumps

• Both the concentration gradient and the membrane potential are forms of potential (stored) energy that can be harnessed to perform cellular work.

• Cotransport

• Cation exchange

Fig. 36.2a

• Water Potential=Pressure Potential+Solute Potential

• Explain this..

Water Potential ..Revisited

• Note;

• 1990s – realized osmosis TOO FAST

• FOUND Both plant and animal membranes have specific transport proteins, aquaporins,

• Aquaporins affect the rate at which water diffuses

• Manufacturing Aquaporins, cells might be able to regulate osmotic rate.

Aquaporins

• Vacuolated plant cells have three major compartments (WALL, CYTOPLASM,VACUOLE)

• The membrane is a barrier between two major compartments: the wall and the cytosol.

• Most mature plant have a third major compartment, the vacuole.

III - Radial (lateral) Transport

Fig. 36.6a

Three routes are available for lateral transport

• #1, substances move out of one cell, across the cell wall and membranes, and into the neighboring cell.

• This transmembrane route requires repeated crossings of plasma membranes. FAST

• #2, via the symplast, requires only one crossing of a plasma

membrane. FASTER• After entering one cell, solutes and water move from cell to cell via

plasmodesmata.

• #3 is along the apoplast, the extracellular pathway consisting of cell

wall and extracellular spaces. FASTEST• Rapid, non specific.

• In most plant tissues, two of the three cellular compartments are continuous from cell to cell.

• Plasmodesmata connect the cytosolic compartments of neighboring cells -

• This cytoplasmic continuum, = symplast route

• Between wall and membrane= apoplast.

Fig. 36.6b

WHAT IS THE FUNCTION OF THE CASPARIAN STRIP????

Fig. 36.7

This is a really important picture….

• Diffusion in a solution is fairly efficient for transport over distances of cellular dimensions (less than 100 microns).

• However, diffusion is much too slow for long-distance transport within a plant

• What cells make up phloem?

• What cells make up xylem?

IV Bulk flow functions in long-distance, longitudinal transport

• Water and solutes move through xylem vessels and sieve tubes by bulk flow; the movement of a fluid driven by pressure GRADIENTS.

• In phloem, for example, hydrostatic pressure drives flow.

• In xylem, it is positive pressure below (cation exchange)*, negative pressure above (transpiration)*

*Understand what drives these and what regulates them

• Flow rates depend on a pipe’s internal diameter.

• To maximize bulk flow;

• the sieve-tube members are almost entirely devoid of internal organelles.

• Vessel elements and tracheids are dead at maturity.

• The porous plates that connect contiguous sieve-tube members and the perforated end walls of xylem vessel elements also enhance bulk flow.

• QUESTIONs;

• How is bulk flow regulated???

• What drives/regulates cation exchange??

• What compromise issues do plants have to face as they transport materials?