Transport in plants What needs to be transported? Structural details about xylem and phloem… How does stuff get into plant cells? What about water flow? Refer to chapter 25 in text.

What needs to be transported? H 2 O to maintain turgor (an important structural element), act as a solvent, and as a transport medium. (Relatively incompressible.) CO 2 to be used in photosynthesis and lost in respiration. O 2 as waste from photosynthesis and e - receptor in respiration. Sugar to provide energy throughout plant, or to be sent to storage. Minerals from roots as building blocks and as ions in reactions. NB: Picture implies plants don’t respire…

Composed of tubes of dead cells with holes in the end walls Tracheids: long, tapered, lignin-thickened tubes. (This is also an important structural element.) Water can move laterally through pits. Vessel elements: shorter, wider, thinner- walled tubes with holes in the end walls. Structural details about xylem…xylem: transports water and minerals. ← More adhesion: Better in low transpiration. ← Relies on strong cohesion to move water.

Sieve tube: column of sieve members, which have cytoplasm but no nuclei (living…ish). Sieve plate between cells; full of holes. Companion cell is still fully alive. There are still plasmodesmata laterally. Structural details… about phloem

Assignment Go to this web site: Plant-Physio-Hopkins Read section 9.4, starting page 157 (It is only a couple pages, but feel free to cruise more of this text.) Write a brief summary of the part about aphid stylets. While online, find an article about using stylets and radioactively-labeled carbon dioxide, cite, and briefly summarize the work.

How does stuff get into plant cells? 1. Active transport and facilitated diffusion: An electrochemical membrane potential, established by active transport of protons out of the cell, drives a lot of transport into the cell for things that don’t enter by direct diffusion. proton pump: the protein complex that uses ATP to pump H + out of the cell. - Net positive charge outside cell. - Higher [H + ] outside cell. - Higher pH inside cell. This establishes the gradient that will be used for cotransport…

Cotransport -The H + is returning down its gradient: The cotransport protein carries (in this case sucrose) against its own gradient. This example of cotransport is within the plant (sugar from one cell to another). There are additional considerations for things coming in through the roots…

↓Soil tends to have a negative charge, which holds onto cations ( + ions). Ion exchange can occur, freeing the needed cation, which then flows down the electrical gradient through transport proteins (channels) cont., specifically dealing with roots:

Anions (- ions) won’t bind to soil, but also can’t diffuse against the electrical gradient. These are imported using symport, (same-way cotransport) like the sucrose example seen before.

How does stuff get in 2. Mycorrhizae: the filamentous hyphae of fungi. These can form a mutualistic symbiotic relationship with plants. (They live closely intertwined lives; both benefit.) - The plant delivers photosynthetic products directly to the fungus. - The fungus delivers hard-to-collect minerals (especially phosphate ions) directly into the plant roots. - This also effectively multiplies the absorptive root surface available to the plant (remember the role of root hairs). ← fine fungal mycorrhizae on roots. on right→ redwood seedling with mycorrhizae: on left, one without them.

Ectomycorrhizal fungi: Hyphae travel along outside of root, and perhaps along cell walls (apoplasty). Endomycorrhizal fungi: Hyphae cross the root cell wall, but do not enter the cytoplasm. Mycorrhizae (cont.)

How does stuff get in? 3. Mass flow of water In order to move materials through phloem: Active transport/active movement of sugar (sucrose) and amino acids at the source into phloem causes the water potential of phloem contents to become more negative. Therefore water follows by osmosis. This means the hydrostatic pressure in phloem increases, which causes mass flow. At another part of the plant the sugars are removed from the phloem (a sink) so the gradients are maintained. (Sources are leaves and storage organs: sinks are stores, fruit, seeds, and roots.)

What about water flow? Transpiration Stream: the path of water through a plant. - Water enters roots by osmosis following the water potential caused by imported minerals. - It travels through xylem due to capillary action: adhesion to walls, cohesion to other water, and upward pull caused by - Transpiration: “the loss of water vapor from leaves and stems.”

Stomata - The guard cells control the movement of gases and water vapor in and out of leaves. - Basically water turgor causes the opening: What controls the turgor…? Abiotic factors can affect transpiration rates: - air temperature - relative humidity - wind - light Adaptations help plants deal with extreme conditions… (Which ones do you remember?)

- If Potassium ions are passively transported into guard cells (as a response to active transport of protons out…) they become hypertonic, and water osmosis follows. - K + flow is regulated by: dawn’s light triggering blue wave receptors, low levels of CO 2, and circadian rhythms. - Abscisic acid (a plant hormone), produced in roots in response to stress causes K + to flood out of guard cells through channels (closing them).

Compare and contrast xylem and phloem Describe at least five xerophytic adaptations How do materials enter plant cells? (3 mechanisms) Track, in detail, water’s entire path from outside to back outside of a plant. How do guard cells work? What holds plants up?

turgoranion tracheidsymport pitmycorrhizae vessel elementmutualistic sieve tubesymbiotic sieve memberectomycorrhizal sieve plateendomycorrhizal companion cellmass flow of water aphid styletsource membrane potentialsink active transporttranspiration stream proton pumpguard cell cotransportabiotic cationabscisic acid ion exchange