TRANSPORT IN PLANTS CHAPTER 36

The algal ancestors of plants were completely immersed in water and dissolved minerals. Terrestrial adaptation: - roots: absorb water and minerals from the soil - shoots:exposed to light and atmospheric CO 2. This morphological solution created a new problem: the need to transport materials between roots and shoots. Vascular tissues transport sap throughout the plant body. Introduction

Transport in plants occurs on three levels: (1) the uptake and loss of water and solutes by individual cells (2) short-distance transport of substances from cell to cell at the level of tissues or organs (3) long-distance transport of sap within xylem and phloem at the level of the whole plant.

Cell membrane is selectively permeable. Passive Transport: -Simple Diffusion -Osmosis -Facilitated diffusion (transport proteins) Active Transport: need ATP energy -Chemiosmosis (proton pump) -Charge Gradient -Cotransport Cell Transport Processes

Simple Diffusion

Osmosis

Facilitated Diffusion

Passive Versus Active Transport

Chemiosmosis

Uses the attractive-repulsive properties of ions to move other ions across membranes Charge Gradient

Plant Cell Structure cell wall chloroplastchloroplast nucleusnucleus central vacuole

Cotransport

Water Relations of Plant Cells

Differences in water potential drive water transport in plant cells

Refers to the tendency of water to leave or enter the cell. Measured in megapascals (MPa; y = 1MPa = 10 atm). Measured relative to pure water in which y = 0 Mpa. If solution draws water away from pure water then the water potential of the solution is less than 0 (y < 0). If solution looses water to pure water then the water potential of the solution is greater than 0 (y > 0). Water potential of a solution is a combined effect of solute concentration and pressure (or tension) on the system. Water Potential

Plasmolysis cell shrinking

Turgor Pressure cell swelling

Bulliform Cells

Short-Distance Versus Long-Distance Transport

Involves simple diffusion, osmosis and active transport.Involves simple diffusion, osmosis and active transport. RoutesRoutes Cell-to-Cell Across Cell Membranes Cell-to-Cell Across Cell Membranes Symplast (involves cytoplasm and plasmodesmata) Symplast (involves cytoplasm and plasmodesmata) Apoplast (transport through porous cell walls) Apoplast (transport through porous cell walls) Involves simple diffusion, osmosis and active transport.Involves simple diffusion, osmosis and active transport. RoutesRoutes Cell-to-Cell Across Cell Membranes Cell-to-Cell Across Cell Membranes Symplast (involves cytoplasm and plasmodesmata) Symplast (involves cytoplasm and plasmodesmata) Apoplast (transport through porous cell walls) Apoplast (transport through porous cell walls) Short-Distance Transport

Involves transpiration and root pressure.Involves transpiration and root pressure. Continuous tube of water depends upon water cohesion and adhesion.Continuous tube of water depends upon water cohesion and adhesion. Involves transpiration and root pressure.Involves transpiration and root pressure. Continuous tube of water depends upon water cohesion and adhesion.Continuous tube of water depends upon water cohesion and adhesion. Long-Distance Transport

Short-Distance Transport

Long-Distance Transport

Transpiration

Stomatal Opening and Closing Guard Cells Mediate Transpiration

Stomatal Opening and Closing

Sugar Loading into Sieve-tube Members

Interaction Between Xylem and Phloem

Guttation: root pressure forces excess water out of leaf Transpiration at night is low Roots accumulates minerals and ions, which build up root pressure Excess water is forced out of leaf

Plants adapted to arid climates, called xerophytes, have various leaf modifications that reduce the rate of transpiration. Many have small, thick leaves, reducing s.a. A thick cuticle Waxy coat During the driest months, some desert plants shed their leaves, while others (such as cacti) subsist on water stored in fleshy stems during the rainy season Xerophytes have evolutionary adaptations that reduce transpiration

In some xerophytes, the stomata are concentrated on the lower (shady) leaf surface. Trichomes (“hairs”) also help minimize transpiration by breaking up the flow of air, keeping humidity higher in the crypt than in the surrounding atmosphere. trichomes stomata

Let’s see some TRICHOMES!