Plant Transport

Transport Overview

SugarsWater and minerals

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