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 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 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?