Plant Hormones

Plant Hormones

1. Hormone: is a chemical messenger produced in one part of the body that affects activities in another part of the body.

2. These are three of the most discussed:a. Auxins, Gibberellins and Abscisic Acid

3. Auxins

a. Auxins are hormones that control phototropism.

b. Auxins work by causing cells on the shaded side of a stem to grow longer than those on the sunlit side. This bends the stem towards the light

3. AuxinsC. High concentrations of auxins also

keep leaves and ripening fruit on trees.

D. When auxin concentrations decrease, usually in autumn, the ripe fruit and worn out leaves fall from the trees

2. Gibberellinsa. Gibberellins are growth hormones

that control plant height and bud development.

b. Tissues in seeds release gibberellins to signal the seed to germinate, or sprout.

5. Abscisic Acid

a. Abscisic acid is a hormone that slows or stops the growth and cell division in plants.

b. Plants typically release abscisic acid during periods of stress, such as a drought or cold.

Abscisic Acid

6. Defense!

a. Plants have several lines of defense against pathogens (disease causing agents) such as bacteria, viruses and fungi (not the good relationship with fungi…like lichens).

b. These pathogens can enter through the stomata, roots and even go through breaks in the epidermis

i.1st Line of DefenseA plant can secrete chemicals

that attack a pathogen directly by breaking down a bacterial cell wall.

ii. 2nd line of defense- Lignin

1. Lignin is a chemical that causes a plant’s cell walls to harden.

2. When a plant makes lignin to fight an infection, it directs the lignin production to the cells containing and surrounding the pathogen.

3. This traps the pathogen in one location to prevent it from invading the rest of the plant

iii. 3rd Defense: Kill neighboring cells1. When a pathogen is detected in

a cell, the plant might send out chemicals that kill neighboring cells.

2. Killing these cells eventually kills the invading pathogen by eliminating the nutrients that it needs to survive.

C. Other means of survivali. Some plants secrete chemicals

that give them a bad taste or smell.

ii. Others are toxic to other organisms or that cause sickness or discomfort.

iii. Examples include poison oak or poison ivy

Practice Question #1

1.) Which type of response is the growth of a flower toward light?

A.) thigmotropismB.) geotropismC.) phototropismD.) dormancy

Practice Question #2

2.) Which plant hormones are most responsible for controlling plant height?

A.) Abscisic acidsB.) AuxinsC.) Nucleic AcidsD.) Gibberellins

Practice Question # 3

3.) Which of these responses aids a plant in fighting infection by a virus?

A.) Increased transpirationB.) Decreased transpirationC.) Increased lignin productionD.) Cell division

Practice Question #44.)Wind causes a potted plant on a patio

to fall over. In a few days, phototropism causes the plant’s stem to begin growing upward. To what external stimulus is the stem responding?

A.) TouchB.) TemperatureC.) SunlightD.) Water