Lesson 8Understanding Plant Growth Regulators

Next Generation Science/Common Core Standard Addressed.

HS‐LS1‐2. Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli.

HS‐LS1‐3. Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.

Bell Work!

Let’s talk for a moment about yourself. What are some differences between your present body and the one you had as a child?

What kinds of chemicals were involved in those changes?

These chemicals are called hormones; for example, estrogen, testosterone, adrenaline, etc.

What chemical changes so plants undergo?

Is it possible to control changes in plant life cycles? If yes, explain.

Bell Work Cont.!

Terms!

Abscisic acid

Apical dominance

Auxins

Cytokinins

Ethylene

Gibberellins

Phototropism

Plant hormones

Thigmotropism

Interest Approach Continued

Plants also experience growth changes with the help of hormonesSometimes these changes

are more dramatic than what you experienced!

Take a look at this plant to the right which fell over the night before. What happened to the plant?

What Do Plant Growth Regulators Do?

Plant growth regulators are chemicals which affect the plant in many complex waysThey can control such activities as cell

division and differentiation, root and shoot growth, flowering and ripening

Plant growth regulators which are made by the plant are called plant hormonesThey are moved around the plant in very

low concentrations

Some growth regulators are man-made, or syntheticThey can be applied

to plants to obtain a wide variety of changesThese changes often

make the plant better or more saleable!

Which grapes would you rather eat?

The ones on the left were treated with gibberellic acid to make them larger.

What Are the Functions of Several Plant Hormones?

Several hormones are made by tissues of the plant

Each hormone has many different jobs, thus they are very much like human hormones

There are five groups of plant regulators: auxins, cytokinins, ethylene, gibberellins and abscisic acid

Auxins This growth hormone is produced by the tip, or

apical meristem, of the stem

It causes the stem cells to elongate and divide

They also flow down from the tip of the stem, preventing lateral buds from sprouting until needed

There are three major affects caused by auxins on the plant

Effects of Auxin on Plants

1. Auxin causes the tip of the middle stem to grow at a faster rateThis is known as apical

dominance Apical dominance is why

many conifers have a pyramid shape

It can be overcome by cutting off the dominant or terminal stem, losing the source of auxin

This trunk should be a single stem; however, the terminal bud was removed forcing it to branch.

2. Auxins are responsible for allowing a plant stem to grow toward the sunThis is known as

phototropismSunlight slowly breaks

down auxin; When the side not exposed to the sun grows faster, the stem bends towards the light

The left side of the plant was exposed to the sun. The right side had shade and grew faster.

3. Auxins allow a plant to respond to the touch of a person or other objectThis is known as

thigmotropism

The repeated touch of an object causes less auxin to remain on that side of the stem

When the auxin side starts to grow faster, the plant grows towards the object and ultimately wraps around it

Cytokinins

These are hormones that are mostly responsible for cell division and differentiation

They are produced in the root tips in seeds

They tend to travel up the stem

In tissue culture, cell division or root growth can be encouraged by adjusting hormones in the agar. If given higher levels of auxins in the agar, roots are produced. If given higher levels of cytokinins, shoots multiply.

Ethylene

This is a gas that affects the plant like a hormone

It is produced in ripening fruit and dying plant material

It stimulates flowering in some plants and causes other fruits and flowers to ripen more quickly and evenly

Effects of Ethylene

Ethylene gas is why fruit will ripen faster in a paper bag, than on the counterThe bag helps to

concentrate the gas in a specific area

Ethylene has a negative effect on cut flowers & foliages It causes them to age more

quickly, reducing their useful life

In this experiment, two holly twigs were placed under separate jars for a week. At the same time, an apple was placed in the second jar. The ethylene given off by the apple caused the holly to lose its leaves and die.

Gibberellins

These hormones cause the internode of a stem to elongate and cell division to occur

They are produced in the stems, roots and young leaves

Gibberellins are commonly used on commercially grown dessert grapes to spread the fruits out and cause them to be bigger

Flowering of plants and the breaking off of seed dormancy can also be achieved by adding gibberellins

Effects of Gibberellins

The cabbage plants on the left were grown on their own

The plants on the right were given gibberellic acid once a week for eight weeksNotice the long stems and

flowers at the top of the plants on the right

They are a result of this hormone

Abscisic Acid

This hormone inhibits (prevents) growth

It is found in seeds which are dormant and in dying leaves

It also appears to help a plant prepare its buds for winter

The dormant bud on the left has a high concentration of abscisic acid. As spring nears, the acid level drops and the bud begins to develop a new shoot.

What are Several Commercial Uses for Plant Growth Regulators?

Synthetic growth regulators are very useful for commercial plant crops

They can save money, time and can lead to a better crop

There are at least three commercial uses of regulators:1. Growth regulators are routinely sprayed on

crops such as poinsettias, Easter lilies and mums to reduce size and make a shorter, bushier and more attractive plantProducts such as A-rest, B-nine, Cycocel and

Florel are commonly used

2. Growth regulators are commonly used to help plants root more completely

These are often sold as a powder under the names Rootone and Hormodin

3. Ethylene gas is used commercially to ripen bananas once they get to market and to induce flowering in pineapple crops

Summary

What is a plant growth regulator called and what does it do?

What is the difference between a plant hormone and a synthetic hormone?

Where in a plant is auxin produced?Explain how apical dominance works in

a plant.How is phototropism different from

thigmotropism?

Summary continued

What do cytokinins control?

How does ethylene effect plants?

What does gibberellin cause in a plant?

What does abscisic acid control?

Name one way that hormones are used commercially to control plants.

The End!