Movement of Water at the Tissue/Organ Level

From Cell to Cell, Through the Root to the Stem

Apoplast Symplast

Water Absorption by Roots • Surface is increased by:– Root hairs– Mycorrhizae - 90% of terrestrial plants• Fungus attached to roots– Hyphae form a mycelium – Hyphae grow into the root , between plant’s cells

Apoplast Symplast• Water and minerals are passed from the root

epidermis through the cortex to the stele via apoplast or symplast

Water Movement Through Tissues• Symplast – pathway through the cytosol of

adjacent cells via plasmodesmata• Apoplast – water movement through the cell walls • Transmembrane - slow

Symplast Pathway• Central vacuole – stores water/minerals– Tonoplast - membrane • Proton pumps in the tonoplast,

pump H+ into the vacuole• Other active transport moves

soil minerals into the vacuole (K+)• Makes the cytosol hyposmotic

(increases Ψs )

Apoplast Pathway• Materials flowing along the apoplastic route are

blocked by the waxy (suberin) Casparian strip at the endoderm

• Must enter endodermal cells to move into the xylem– Enables endodermal cells

to extract (active transport) minerals from soil

Movement Through Tissues• Water passes through the cortex to the stele

(xylem – tracheids/vessel elements)