PlantTransportChapte r37

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Transport in Plants : 

Transport in Plants Chapter 37

Outline : 

Outline Overview of Water and Mineral Movement Water Potential Water and Mineral Absorption Water and Mineral Movement Bidirectional Phloem Transport

Overview of Water and Mineral Movement : 

Overview of Water and Mineral Movement Most nutrients and water enter plant through roots, and move upward in xylem. Water moves through spaces between cell protoplasts, plasmodesmata, cell membranes and xylem. Osmosis is enhanced by aquaporins (water channels) in vacuole and plasma membranes. Transpiration “pulls” water through stomata. cohesion adhesion

Water Movement Through A Plant : 

Water Movement Through A Plant

Water and Mineral Absorption : 

Water and Mineral Absorption Most water absorbed through root hairs solute potential greater than surrounding soil energy expenditure required to accumulate ions in root cells proton pumps Water and ions must pass through plasma membranes and protoplasts of endodermal cells to reach the xylem.

Mineral Transport in Roots : 

Mineral Transport in Roots

Water and Mineral Absorption : 

Water and Mineral Absorption Root pressure - movement of water into the plant and up the xylem columns despite absence of transpiration Active transport increases solute potential of roots. High root pressure may lead to guttation. occurs through groups of cells located near edge of leaf

Water and Mineral Movement : 

Water and Mineral Movement Evaporation from leaves produces a tension on entire water column extending down to the roots. Water has inherent tensile strength that varies inversely with the diameter of the column. Air bubbles cause xylem to fail. Plants must admit carbon dioxide, but must control water loss.

Transpiration : 

Transpiration

Water and Mineral Movement : 

Water and Mineral Movement Regulation of transpiration Stomata open and close due to changes in turgor pressure of guard cells. Turgor results from active uptake of potassium (K+) ions. Increase in K+ concentration creates a water potential that causes water to enter osmotically, guard cells to become turgid, and stomata to open.

Slide 11: 

Some other facts about the stomata Open in the day and closed at night - need carbon dioxide in the daylight for photosynthesis When water is scarce, plant wilts and guard cells become flacid Abscisic acid - plant hormone that causes K+ to pass out of cells and guard cells become flacid High levels of CO2 cause guard cells to become flacid Leaves lost when water is scarce

Water and Mineral Movement : 

Water and Mineral Movement Other factors regulating transpiration carbon dioxide light temperature Water loss regulation dormancy deciduous leaves thick, hard leaves trichomes

Water and Mineral Movement : 

Water and Mineral Movement Plant response to flooding – depletes oxygen fresh water aerenchyma - loose parenchyma tissue with large air spaces oxygen transported from above-water to below-water structures

Aerenchyma : 

Aerenchyma

Plant Response to Flooding : 

Plant Response to Flooding Salt water Salt must be excluded, actively secreted, or diluted as it enters. Mangroves have pneumatophores.

Phloem Transport is Bidirectional : 

Phloem Transport is Bidirectional Translocation - distribution of carbohydrates manufactured in leaves to rest of the plant Energy requirements for phloem transport mass-flow hypotheses Dissolved carbohydrates flow from a source and are released at a sink.

Slide 17: 

Translocation - Distribution of nutrients, especially carbohydrates, through the phloem – “source and sink” Osmosis plays an important role Phloem loading - Sucrose is actively loaded into phloem tubes Water moves in and carries sucrose along passively No energy required for this process - but Loading and unloading sucrose in phloem tubes does require energy Companion cells of phloem provide the ATP

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