9.2 Transport in the Phloem of Plants

Phloem Vascular tissue that transports sugars and amino acids throughout the plant

Translocation The process of moving organic material through the phloem Uses energy in the form of active transport to carry organic material from source (location of synthesis) to sink (location of use) Since there is active transport the tissue needs to be living. Therefore phloem is alive and functional at maturity. However it is hallow for materials to move

Cells that make up Phloem Sieve Tubes (hallow) Companion cells (house mitochondria and nucleus which regulate products for both cell types) Connected by Plasmodesmata (channels)

Movement of molecules Apoplastic movement Material moving through the cell walls within plant tissue Symplastic movement (used in translocation) Movement through the plasmodesmata after entering the cytoplasm of a plant cell

Plasmodesmata

Source of organic molecules Leaves of plants (photosynthesis) Underground roots and stems (store carbohydrates) Bulbs, tubers, storage roots Act as the source but can also be sink Therefore translocation occurs in all directions

Location Xylem and phloem lie adjacent to each other Allows water to move easily Osmotic gradient causes water to move into phloem Organic materials move from source to sink from areas of high concentration to areas of low concentration

Turgor Pressure The water pressure inside plant cells Can also be called hydrostatic pressure

Transpiration Vs. Translocation Passive: water diffuses into the xylem and evaporates from the leaves Active: sucrose and amino acids are pumped into the phloem Transports water and minerals Transports sucrose, amino acids and hormones Consists of vessel elements and tracheids Consists of sieve tubes and companion cells Dead at functional maturity Alive at functional maturity Moves water and minerals from the roots to the shoot (one direction of travel) Moves organic molecules from the source (leaves or storage organ) to the sink (growing plan structure: fruits, seeds, roots)

Xylem and phloem in Dicot root and stem cross sections

Vascular tissue Vascular bundle: Holds the xylem and phloem Vascular cambium: located between the xylem and phloem Made of undifferentiated cells to become either xylem or phloem