PLANT MOVEMENT

Higher plants, being fixed to soil, cannot move from place to place. Really, have you ever seen a tree with legs?! Yikes.

However….. within the plant body various mechanisms are in constant motion!

For example, there is movement of:

water

minerals

food

hormones

and, more!

Just when you thought plants just stood there looking green… now you know there’s a lot of action going on inside those plants!

Certain parts of the plant body (in response to external stimuli) show physical displacement called movement.

Even lower unicellular (one-celled) plants also show movement from place to place. Such movements may be autonomic (automatic) or induced(created from another place).

Plants move in response to:

* light

* touch

* chemicals

* temperature

* gravity

* H2O

Factors that cause movement

are called stimulus.

The place that receives the

stimulus on the plant is called

the perception site.

The plasma membrane is

necessary for the message to

be able to pass from one place

to another so that the plant

can respond properly.

There is a time delay between the time thestimulus is applied and the time theresponse begins.

This time is called reaction time.

The time required to cause the proper stimulus is called presentation time.

Once the plant responds to the stimulus the plant structures always come back to their original position.

This process is called recovery and the time required is referred to as relaxation time, which varies from species to species.

Ahhhh…..I’m chillin’ now!

Drum roll, please…..

These that happen because of:

▪ Internal stimuli▪ External stimuli

Turgor movements

Turgor movements happen because of changes in the internal water pressure of the plant. Turgor movements are often (but not always) started by contact with objects outside of the plant. They are:

▪ “Sleep” movements▪ Solar tracking▪ Water conservation movements

We will talk about several categories of plant movements:

1. Nutations – Charles Darwin observed spiraling movement

of the growing tip. This type of movement is common to many plants.

2. Nodding Movements – This is a slow, oscillating

movement that appears like the emerging stem (hypocotyl) “nods” from side to side like an upside down pendulum.

3. Twining Movements – Tendril twining, which starts

once the tendril comes into contact with an object. This action happens when the cells elongate on one side and shrink on the other side.

4. Contraction Movements – contractile roots of bulbs

5. Nastic Movements - occur in response to environmental stimuli but unlike tropic

movements, the direction of the response is not dependent on the direction of the stimulus. Some of the most spectacular plant movements are nastic movements. These include the closing of the carnivorous Venus Flytrap leaf when it captures prey or the folding of the mimosa leaf when it is disturbed.

Tropisms are movements in one direction that occur as a result of an external stimuli. Tropic movements are in three phases:

1. Perception phase when plant receives a stimulus on one side.

2. Transduction happens when one or more hormones are unevenly distributed which results in

3. Asymmetrical growth (where one side of the plant has greater cell elongation than the other.)

There are two tropisms we will investigate:

Turgor movements are reversible changes in the position of plant parts due to a changes in internal water pressure and are often, but not always, started by contact with objects outside of the plant.

The movement of Mimosa pudica (Touch-me-not) leaves when touched is an example of turgor movements. Another example of this is the reaction seen in the Venus fly trap when an insect lands inside its leaves.

http://www.youtube.com/watch?v=PRo4rg07_gg&feature=fvwp&NR=1

http://www.youtube.com/watch?v=o3hk9Sz--h4

➢ the movement is always a growth movement

➢are responses by part of a plant towards or away from a stimulus coming from one direction

Negative –if growth is away from the stimulus

Positive –if growth is towards the stimulus

Gravity

Growth

Growth

➢ is a growth response to light

Light

Geotropism

➢is a growth response to gravity

POSITIVELY PHOTOTROPIC

NEGATIVELY GEOTROPIC

➢ Towards light:

✓ To trap more light for photosynthesis

➢ Away from gravity:

✓ shoot of a germinating seed grows out of the soil

✓ more chances for pollination & seed dispersal

✓ To anchor the plant

✓ To search for water

✓ To ensure that the root of a germinating seed always grows downwards, whatever, the position of the seed in the soil