Lec 7: Phloem

What do palisade cells have inside them?

chloroplasts

What happens in the palisade during sugar transport from the leaf? STOP at the location before it goes out the palisade.

in chloroplasts —> calvin cycle produces G₃P —> G₃P moves out of the chloroplast into the palisade cytoplasm —> in the cytoplasm —> G₃P makes glucose and fructose —> glucose and fructose combine (or dehydrates and synthesizes) to make sucrose

Where does the sucrose move once it is made?

Sucrose passively transport —> palisade thru the PD —> into the bundle sheath n phloem of the minor vein —> cell walls of the CC and STM

What type of sugar is glucose and fructose?

monosaccharides

What type of sugar is sucrose?

disaccharide

Who is the transport sugar?

sucrose

How does sucrose move from the cell walls of the CC and STM into their (CC’s and STM’s) cytoplasm?

phloeom loading —> sucrose co-transport protein actively transport sucrose and H⁺ into the CC’s and STM’s cytoplasm

Why is the transport of sucrose into the CC’s and STM’s cytoplasm active?

keep toxins out of the plant’s systemic system

Once the sucrose is in the cytoplasm of the CC and STM, is water potential high or low in their cytoplasm? Is water flowing in or out? From where?

low water potential, so water flows in from the xylem

Why is it important that the xylem and phloem are next to each other?

sugar movement bc the sugars will flow into the phloem and water will flow from the xylem into the phloem

Once the phloem is loaded with sucrose and water, how does sucrose and water flow thru the phloem and xylem?

As transpiration pulls up water in the XVMs, the water is sucked into the phloem —> in the CC’s and STM’s —> sugars are passively pushed/pressurized by bulk flow

What is a source?

where sucrose is transported out of

What is a sink?

where sucrose is transported into

Give example(s) of fall source(s) and spring source(s).

Fall - leaves and stem

Spring - tubers, rhizomes, bulbs, and roots

Give example(s) of fall sink(s) and spring sink(s).

Fall - tubers, rhizomes, bulbs,and roots

Spring - flowers, fruits, leaves, buds, and stems

Are young leaves sinks or sources? What about mature leaves?

young - sinks

mature - sources

Explain the concept of these photos.

Aphid feed on the sugars in the phloem —> phloem is located near the bottom of the leaf —> Aphid stick their probosci into the STMs —> sugars are pressurized —> the sugar comes out as a sap droplet from the butt of the aphid.

Pressurized: air is forced in a airtight enviroment, till the amount of air inside is enough to increase the pressure.

After the sucrose travels from the minor veins, where does the sugar go next?

major vein —> out of the petiole —> to sinks