Transport Overview of long distance transport Transport Starting small regulation of solute transport across plasma membranes Plants burn energy ATP to pump protons across cell membrane Transport Starting small regulation of solute transport across plasma membranes Transport proteins use membrane potential or proton gradient to regulate solute flow Transport Starting small regulation of solute transport across plasma membranes Transport proteins use membrane potential or proton gradient to regulate solute flow Transport Starting small regulation of solute transport across plasma membranes Ion Channels are specific for a certain ion Transport Cell walls are permeable to water and solutes these materials can move through plant tissues passively by diffusion Cell to cell transport Apoplast Apoplastic transport Transport Most all cytoplasm of plant cell is continuously connected via Cell to cell transport plasmodesmata Symplast Transport Cell to cell transport Transmembrane route Transport Diffusion and active transport through the apoplast symplast or transmembrane roots is sufficient for short range movement of materials Long distance transport depends upon bulk flow through the xylem and phloem Transport Water and mineral uptake by roots Epidermal cells near tips of roots absorb most water and minerals especially root hairs Transport Water and mineral uptake by roots The walls of the endodermis have a waxy barrier termed the Casparian strip No apoplastic entry into the vascular bundle the stele Transport Once in the xylem water transport by bulk flow is rapid and prolific Some trees transport at 30 m hr A single maize plant moves 60L of water over a growing season What creates the force for this movement against gravity Root pressure pushed from the roots Transpiration pulled from the leaves Transport Root pressure Active transport of solutes into stele lowers stele s water potential Water flows into stele increasing pressure forcing water up the xylem Guttation Minor mechanism Transport Transpirational pull of water through xylem depends on unique chemical properties of water 1 Cohesion 2 Adhesion Transport Transpirational pull of water through xylem depends on unique chemical properties of water 3 Surface tension Transport Transpiration occurs within a film of water in the cell walls of leaf mesophyll cells Surface tension is negative pressure potential Transport The sucking force of negative potential is transmitted via cohesion Adhesion to cell walls of tracheids and vessel elements helps to fight gravity Transport Bulk flow in the xylem is driven by the negative water potential created by transpiration entirely by P Driven Transport Cavitation Formation of a vapor bubble A failure of cohesion Transport The conflict between photosynthesis and water loss Transport Stomata regulate the amount of gas exchange and water loss through transpiration Transport Changes in turgor pressure inflate or deflate guard cells changing the stoma size Transport Guard cell turgor is controlled by regulation of K uptake Transport Phloem sap also moves by bulk flow Movement is always from source to sink Sources and sinks can switch Transport Sugars from source tissues into sieve tube elements by both symplastic diffusion and active loading from the apoplast Transport Active transport of sugar depends on energy from the proton pump Transport Sugars from source tissues into sieve tube elements by both symplastic diffusion and active loading from the apoplast Transport The Pressure flow hypothesis for phloem movement 1 Phloem near source S lowered Transport The Pressure flow hypothesis for phloem movement 2 Phloem near source water rushes in P increases Transport The Pressure flow hypothesis for phloem movement 3 Phloem near sink sugars are withdrawn increasing S Transport The Pressure flow hypothesis for phloem movement 4 Phloem near sink water exits and is recycled in the xylem Transport Aphids feed by injecting mouthparts directly into the phloem Transport Xylem and Phloem harness simple physics and chemistry to accomplish transport by bulk flow Transport Phloem is an information superhighway Many plant viruses spread through the phloem Functional messenger RNAs can be transported long distances in the phloem Signals indicating infections are moved through the phloem For instance RNA interference defense against viruses uses phloem transport
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