# Chapter 36

## Overview of plant behavioral responses

- Behavior is a response of an organism to an internal or external stimulus
- types of plant behavior 
    - movement 
        - bending,twisting, or rotating 
            - nutation
        - rapid movement as in sensitive plants 
            - response to touch
    - growth
    - seed germination
    - seasonal production of reproductive structures
    - defensive responses to attacks 
        - thorns, spines, chemicals

### Responses to internal and external stimuli

#### Internal

- Internal biological clock 
    - circadium rhythms
- chemical signals 
    - transcriptions factors and other proteins or hormones
    - often interact with each other and external signals

#### External

- light atmospheric gases (CO2 and water vapor) temperature, touch, wind, gravity, water, rocks, and soil minerals
- Herbivors, pathogens, organic chemicals from neighboring plants, and beneficial or harmful organisms

[![Screenshot-from-2019-02-26-22-04-33.png](https://bookstack.aronwk.com/uploads/images/gallery/2019-02-Feb/scaled-840-0/AKwHs191C5p058bS-Screenshot-from-2019-02-26-22-04-33.png)](https://bookstack.aronwk.com/uploads/images/gallery/2019-02-Feb/AKwHs191C5p058bS-Screenshot-from-2019-02-26-22-04-33.png)

## Plant Behavior

Involves internal and external stimuli

- tropism 
    - growth response that is dependent on a stimuli that occurs in a particular direction
- Reception molecules 
    - located in plant cells
    - sense stimuli and cause response

### Phototropism

- Growth response to light
- light causes movement of hormone auxin away from said light
- result in unequal distribution of auxin 
    - causing unequal cell elongation
- positive tropism

### Gravitropism

- growth response to gravity
- positive tropism 
    - roots
- negative tropism 
    - shoots
- columella cells in root cap/tip region sense gravity

### Thigmotropism 

- Growth response to touch
- roots 
    - columella cells cause roots to grow around obstacles

## Regulation of plant growth

[![Screenshot-from-2019-02-26-22-25-01.png](https://bookstack.aronwk.com/uploads/images/gallery/2019-02-Feb/scaled-840-0/zQSvjIF5b7FKV5Rc-Screenshot-from-2019-02-26-22-25-01.png)](https://bookstack.aronwk.com/uploads/images/gallery/2019-02-Feb/zQSvjIF5b7FKV5Rc-Screenshot-from-2019-02-26-22-25-01.png)

### Hormones

- chemical messengers that regulate plant growth 
    - most transported in phloem tissue
    - all require an expenditure of energy on part of the plant (ATP) for transport
- interact with external environmental stimuli

#### Hormones control

- growth
- seed germination
- flowering
- fruiting
- shedding of leaves
- color change of leaves

### Hormones of two broad categories

- growth inhibiting 
    - mostly fall/winter
    - certain times of the year growth is not good
- growth promoting 
    - mostly spring/summer

### Auxins

- first group of plants hormones to be described
- growth promoting
- produced in 
    - shoot tips, seeds, fruits, leaves, stem
    - NOT in the roots

#### Effects of auxin

##### Promotes

- cell elongation
- shoot elongation
- production of wood
- fruit development

##### Inhibits

- lateral bud development
- absission (falling off) of leaves, flowers, fruits

### Cytokinins

- Originally detected in coconut "milk"
- growth promoting
- prodiced in 
    - seed, fruits, roots

#### Effects of Cytokinins

##### Promotes

- cellular division 
    - named derived from Cytokenesis

##### Inhibits

- senesence 
    - change of color due to breakdown of pigments

### Gibberellins (giberellic acids)

- many types 
    - >200
    - more than any other group
- growth promoting
- found throughout the plant but concentrated in seeds

#### Effects of Gibberellins

##### Promotes

- stem elongation by cell division and cell elongation

[![33d198e813d24ff3a6a43ac45b681b88.jpg](https://bookstack.aronwk.com/uploads/images/gallery/2019-02-Feb/scaled-840-0/1zpChX3Jnj5QZB3Z-33d198e813d24ff3a6a43ac45b681b88.jpg)](https://bookstack.aronwk.com/uploads/images/gallery/2019-02-Feb/1zpChX3Jnj5QZB3Z-33d198e813d24ff3a6a43ac45b681b88.jpg)

- intake of water causes swelling and embryo hydration
- embryo secretes gibberellins
- gibberellins transported to cells of aleurone layer to secrete enzyme
- (alpha-amaylase) for breakdown of endosperm (starchy stored food) to glucose
- embryo will respire glucose to produce ATP
- embryo is directing the timing of plant germination
- Advantage seed plants

### Brassinosteriods

- growth promoting

#### Effects of Brassinosteriods

##### Promotes

- cell expansion
- shoot elongation
- xylem tissue development
- stress response

##### Inhibits

- leaf abscission

### Abscisic Acids (ABA)

- Growth inhibiting
- found in large quantities in seeds. mature leaves, and dormant buds

#### Effects of ABA

##### Promotes

- senesence
- production of storage molecules in seeds

##### Inhibits

- cell elongation
- alpha-amaylase production

### Ethylene

- growth inhibiting
- actually a gas produced by incomplete metabolism
- interacts with the 4 growth promoting hormones to determine cell size and shape

#### Effects of Ethylene

##### Promotes

- fruit ripening
- abscission of leaves, fruits, flowers

## Seed germination

- requires breaking of dormancy 
    - combination of internal and external factors

#### Internal

- hormones
- stored food
- H2O absorption
- embryo swelling

#### External

- sunlight
- temperature
- longer day light
- soil moisture

### Generalized Seed

- Seed coat(s)
- as seed coat cracks
- Radical comes out first 
    - then then shoot

### Seedling

- result of cellular reproduction and increase size
- internal development 
    - cells>tissues>organs>organism