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) **