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Water Transport and Plant Signaling Proton Pumps • Transport proteins that pump H+ out • Membrane Potential is created, negative charge on the inside positive on the outside. • Protons end up flowing back into the membrane, using their movement to do work. Cotransport • The proton gradient is used to actively transport other solutes in. Solute Potential • solute potential (osmotic potential) is proportional to the number of dissolved solute molecules. (always negative) • Determines where osmosis takes water Pressure Potential • Pressure Potential- is the physical pressure on a solution. (negative or positive) • Determines where water is pushed or pulled. Water Potential • Water potential – the combined effects of solute potential and pressure potential. • Determines where water will flow. Water Pressure and Cells • Flaccid- has lost water • Plasmolysis- shrinks and pulls away from the cell wall (lower water potential outside the cell) • Turgid- swells and stays stiff agains the cell wall (lower water potential in the cell) Paths to bring water in • Apoplast- formed by connecting cell walls • Symplast- connecting cytosol of cells • Plasmodesmata- gaps that connect neighboring cells Moving Water In • Root pressure- water flowing into the xylem from the root cortex due to ions in the xylem** Water Up • Transpiration – the loss of water through stomata causing water (xylem sap) to be pulled up xylem (adhesion and cohesion).** Transpiration Regulation • Guard cells, when turgid bow out and open stomata • Day light or decreased CO2 cause stomata to open • Drought or flaccid cells cause stomata to close • Heat, wind, and dry condition cause excess water loss. Moving water down • Translocation- moving sugars down the plants • Source cell- sugar producing (leaves), dumps sugars into sieve tubes • Water (phloem sap) is drawn into sieve tubes • Sink Cell- growing cells that consume sugars, takes sugars from the sieve tubes. Plant Signaling • Hormones and environmental cues are used for signaling • Auxin (IAA) Auxin- primarily causes young cell elongation (loosens the cell wall) and lateral root formation, stops leaves from falling, regulates fruiting, and causes vascular differentiation. Cytokinins • Cytokinins – aid in stimulating cell division • Auxin must be present with cytokinins to cause cell division • The ratio of Cytokinin to Auxin determines what undifferentiated cells become, and control apical dominance. Gibberelins • Gibberelins- promote stem elongation, fruit production, and germination. Brassinosteroids • Brassinosteroids- similar affects as auxin. Also prevents leafs from dropping and causes xylem to differentiate. Abscisic Acid (ABA) • Abscisic Acid – inhibits plant growth. Keeps seeds dormant, closes stomata during drought. Ethylene • Ethylene – causes fruit to ripen, helps seedlings grow around obstacles, apoptosis (senescence), and causes leafs to fall (abscission). Florigen • Florigen- hypothetical flowering hormones Short day and Long day flowers grow on the same plant when grafted. Phototropism • Phototropism – plant response to light • Blue light receptors – controls things such as stem elongation and stomata opening • Phytochromes (red light receptors)- control things such as seed germination and shade avoidance. Photoperiodism • Photoperiodism – a plants response to a period of light. (like flowering). ** • Short Day plants flower in fall (soybean) • Long Day plants flower in spring (spinach) • Day neutral don’t rely on photo period (rice) Gravitropism • Gravitropism- plant response to gravity • Roots respond positively • Stems respond negatively ** Thigmotropism • Thigmotropism – plant response to touch (vines) **