Hachi's posts

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Minor, too weak to overcome gravity, can’t keep pace with transpiration in daytime

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Guttation - root pressure causes more water to enter the leaves than is transpired → droplets on leaves in the morning

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Produces positive pressure

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At night (no transpiration) - root cells pump mineral ions into xylem → lowers water potential in vascular cylinder → water flows in from root cortex → root pressure (pushes xylem sap)

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Transpiration - loss of water vapor from leaves, role in transporting xylem sap from roots to leaves

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Endodermal cells and living cells of vascular cylinder (symplast) discharge water/minerals into their cell walls (apoplast) via diffusion and active transport → tracheids and vessel elements of xylem (apoplast) → shoot system via bulk flow

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Endodermis also prevents mineral ions from leaking back out

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Apoplastic route - minerals are blocked from the vascular cylinder by the Casparian strip (in walls of endodermal cells, made of waxy suberin), so they must first cross the selectively permeable plasma membrane of the endodermal cells before entering vascular cylinder

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Symplastic route - minerals were already screened (had to cross a plasma membrane when they entered this route in epidermis or cortex), so they can continue through the plasmodesmata of endodermal cells into the vascular cylinder

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Endodermis (innermost layer in the root cortex) = controls selective passage of minerals from cortex into vascular cylinder (and then xylem), screens out unneeded/toxic stuff

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Soil solution passes along epidermal walls and extracellular spaces into root cortex → exposes cortex cells to soil solution → increases SA for absorption

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Absorb soil solution, which consists of water and dissolved mineral ions

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Roots - epidermal cells are permeable to water, many are differentiated into root hairs

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Perforation plates (vessel elements) and porous sieve plates (sieve-tube elements) also enhance bulk flow