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Plant Transport Transport Overview Water and minerals Sugars Vascular Tissue • Xylem – Water – Dissolved minerals • Phloem – – – – Water Sugars Amino acids Hormones Uptake of Minerals and Water • Lateral movement – soil to xylem – Diffusion and active transport of minerals • Increased surface area – Root hairs – Mycorrhizae • Symplastic and apoplastic movement – All minerals must pass through a selective membrane – Casparian strip prevents direct apoplastic movement into the xylem Lateral Transport of Minerals and Water from Roots Bulk Flow Transport Through Xylem • Root pressure – pushing water – Active transport of minerals into root creates lower water potential – Water enters cells and is pushed up xylem • Transpiration – pulling water – Water evaporates from leaves – Water pulled up xylem because of cohesion of water molecules – Transpiration controlled by openings in leaf called stoma Transpiration Control of Transpiration • Stoma open – K+ enter guard cell – Cell becomes turgid from influx of water • Stoma closed – K+ pumped out of guard cell – Cell becomes flaccid from efflux of water Photorespiration • Response to high heat and low water • Stoma close to prevent water loss causing low CO2 and high O2 levels in leaf • Carbon fixation low – Carbon is removed from RuBP to produce CO2 – Rubisco runs in reverse Loading of Sucrose into Phloem • Transport is in either direction at different times • Transport from sugar source to sugar sink • Sugar is pumped from source to sieve tube member Mass Flow in a Sieve Tube
