27: Plant Transport and Environmental Responses

Where does water move in plants?

up from roots to leaves

Where does sugar move in plants?

In from leaves, but also from plant to young leaves/roots

Where does water move

From high osmotic potential (high water) to low osmotic potential (low water)

What happens to a plant cell as it loses water

Normal turgid (turgor = pressure in cell) cell

Flaccid cell (cell body not close to cell wall anymore)

Cell body shrunked away from cell wall (plasmolysis)

How do ions, glycose, amino acids, and large polar molecules pass through plasma membranes?

Membrane channels/pumps

What can pass through plasma membranes without help

small, non-polar molecules

O2, CO2, small lipids

How do proteins, starch, and bacteria pass through plasma membranes?

endocytosis

Simple and facilitated diffusion

Simple: just slide through plasma membrane

facilitated: need protein channels, aquaporins

water potential

Ψ = Ψs + Ψp

s = solute potential

p = pressure potential

water moves from higher Ψ to lower Ψ

technically also + Ψcapillary +Ψgravitational, but these are mostly negligable

Can you close stomata but keep water moving up through roots?

NO, if water no leave, the flow stops

What is xylem flow driven mainly by?

Negative pressure, not root pumping

Where do water molecules go in plants?

most is transpired, some used for growth and turgor, tiny used for photosynthesis/metabolism

Xylem girth trade-off

Thicker walls makes flow of water more efficient, but increases risk of cavitation (air bubbles)

How can xylem get cavitated?

Air leaks in from a hole, bubbles form as ice freezes, force of the water being pushed through caves the straw in

Sources and sinks of plants

Source: produces/releases sugar, mature leaves

Sinks: uses/stores sugar, roots, fruits, flowers, young leaves

Phloem and sources and sinks

Phloem can change direction as sources and sinks change

What do companion cells do for phloem

passes sugars and nutrients through channels to keep sieve-tube elements alive

How does phloem sap (sugar water) move through?

leaf cell makes sugar, passes to companion cell

companion cell puts into phloem

increased turgor pressure in that phloem section, sap flows away to decrease pressure, goes into another phloem section

companion cell of that phloem section sucks up the sugar, dumping it into a sink

Developmental plasicity

environment-dependent change in growth, patterning, or developmental timing

What does auxin do?

it’s a hormone that makes the cell it’s in looser, so the cells can stretch and grow longer

helps maintain apical dominance (growth only up/down)

Phototropism

light changes where cell elongate

auxin goes to where there is no light, so the plant becomes longer in the shaded part, making it curve towards the light

Gravitropism

orientation changes auxin distribution

roots show POSITIVE gravitropism (grow with gravity)

shoots show NEGATIVE gravitropism (grow against gravity)

amytoplasts = heavy cotton balls that roll down with gravity, touching the bottom of the root cell. that side then senses amytoplast presence and moves auxin there

at the tip/root cap

When plants germinate?

When conditions change and favor plant growth, Gibberellins (GAs) are released, telling seed to wake up

If conditions bad/meh, Abscisic Acid (ABA) tells seed to keep sleeping