BI 222 Topic 8 How Plants Respond to the Enviornment

Etiolation refers to?

The growth of plants WITHOUT light

What happens to stems of plants undergoing etiolation?

They are long, weak, pale yellow, and have little to no leaves, and a hooked tip.

The pale yellow color of plants in etiolation is because?

Plants don’t do photosynthesis without sunlight.

The long/weak stems of plants in etiolation are due to?

The plant prioritizing growing TALLER

in soil, they also have dirt to provide them structure.

The reason why plants in etiolation will have few/no leaves is because?

Leaves are unnecessary because the plant isn’t photosynthesizing,

They would also get in the way and be damaged under the soil.

Why is the tip hooked on a plant undergoing etiolation?

to prevent damage, as the shoot doesn’t have protection like the root cap does.

Why does a plant in etiolation have few/no roots?

Because their main reason for water intake, photosynthesis, isn’t happening yet.

Stability isn’t needed because the soil is providing that.

De-etiolation AKA Greening, is when what happens?

photomorphogenesis

De-etiolation is regulated by?

phytochrome

Phytochrome

enzymes that regulate photomorphogenesis

Phytochrome is initially synthesized into

“Pr

Pr

(inactive) absorbs red light at 660 nm

Pfr

(active)

absorbs red shade light at 730 nm

The activated version of phytochrome does what?

triggers over 2500 genes.

Shade has a low?

Pr:Pfr ratio

Shade avoidance response is when

in a natural habitat, plants grow taller in the shade to compete for more sunlight.

What causes the shade avoidance response?

Being in the shade means that the phytochrome are inactive, and the plant isn’t triggering the genes of growth.

Positive gravitropism is when

plants work WITH gravity,

roots going down with gravity

Negative gravitropism is

plants working AGAINST gravity

shoots growing up towards the sky

Amyloplasts - AKA statoliths

starch makes these organelles denser, so they follow gravity

In the root cap, IAA is transported _____ roots and here it _____ cell elongation

UP the roots

PROHIBITS cell elongation

When bent, the bottom stops elongating but the top elongates, making the roots,

bend downwards.

Plants are mostly activated by what kind of light?

Blue light!

The Darwin and Darwin experiment told us that whatever was going on with plants that made them bend, it meant that,

the tip of the plant senses the light.

Phototropic 1

PHOT 1

What happens when PHOT 1 absorbs blue light?

It triggers a conformational change resulting in auto-phosphorylation triggering a signal transduction.

What did they do in the 1913 Peter Boysen-Jensen experiment?

They tested putting a gelatin (permeable) and mica (impermeable) block between the tip and body of the plant.

In the 1913 BJ (lmao) experiment they found that

a chemical produced in the tip of the plant diffused down the shoot.

The Frits Went (FW) 1926 did what?

Took the permeable gel used in the BJ experiment and put it on only a half of the width of a plant. This resulted in the plant bending towards the side with the gel, demonstrating the role of auxin in plant growth. T

he FW experiment found what?

Asymmetric distribution of the chemical from the tip of the plan caused cell elongation and bending.

The first plant hormone found was?

Auxin!

Plant Hormones -

chemical signals that move throughout a plant, required in small amounts.

What do plant hormones do?

Allow for the plant to respond to changes in its enviornment.

Auxin does what?

Stimulates elongation of cells, aka, phototropism/gravitropism

Auxin is made where?

In the shoot apical meristem - SAM

Auxin activates what?

Lateral root formation

but can also inhibit, with apical dominance

Auxin activates a _____ in acidity

increase

To elongate a cell, the cell wall becomes acidic, activating enzymes that do what?

cut cross-linked proteins to allow cellulose fibers to losen.

Expansin does what?

Helps cellulose fibers slide.

How does a cell expand to fill in the loose fibers of the cell wall?

By increasing solute potential so water will enter. This increases pressure, and the cell expands.

How does a cell strengthen the loosened wall once expanded?

By adding cellulose cells on the expanded region.

When auxin fertilizer is applied to the roots, this causes

root stimulation

What kind of hormone is in most weed herbicides?

Auxin, which can target dicots and leaves monocots alone. This hormone mimics natural plant growth hormones, causing uncontrolled growth in target plants.

Where is cytokinin made?

In the roots.

What is the function of cytokin?

cell division, with apical dominance. It promotes lateral bud growth and delays leaf senescence.

The antagonistic relationship between cytokinin and auxin means…

Auxin is produced in the shoots, and cytokinin in the roots, meaning that they’re function is more dominant near the area they are made.

What happens when a SAM is cut off?

New shoots will sprout from the cytokinin left unchecked in the absence of auxin.

Gibberellin is made where?

in the meristems, young leaves, and seeds.

Function of gibberellins

Stem elongation, fruit growth, and seed germination

Endosperm-

contains starch to grow seeds

Embryo-

contains DNA

When the embryo absorbs water, it releases _________, which causes the production of _____ then _______

Giberellin

Aleurone cells

alpha amylase

Alpha amylase -

breaks down starch of the endosperm.

Starts and sugars are used to grow?

shoots!

starch → sugar

Fruit treated with gibberellins will?

Grow much larger!

Function of ethylene

Fruit ripening and triple response.

What fruit is a great source of ethylene?

Bananas!

The triple response:

1. Slow stem elongation

2. Thicken it

   1. Horizontal Growth

Senescence

The programmed cell death of leaves in fall.

When undergoing senescence, the plant…

reabsorbs as much nutrients as possible.

When plants lose light for the winter, tehy

break down chloroplasts and stores the components of them in the branches, to be used again in spring.

Leave abscission

where the plants break off at the petiole

(aka - dead leaves drop from the tree.)

Abscisic Acid (ABA)

reduces growth

suppresses bud growth

prevents seed germination

during drought-stimulates stomatal closure.

Abscisic Acid is considered a _________ hormone.

Antagonistic.