Plant Growth Factors Flashcards
Type of growth response to stimulus name
Phototropism = response to light
Gravitropism = gravity
Can be both positive and negative
Name hormone tht is a specific growth factor
Indoleacetic acid (IAA)
What does IAA affect
Synthesised at tips of roots and shoots
Affects elongating region of a plant
How does IAA work
IAA moves into elongating region, binds to protein receptors on cell membranes
Lowers the pH by releasing H2 bonds between microfibrils in cellulose cell walls
Causing cell walls to loosen allowing it to be more easily stretched
Describe how IAA controls elongation in detail
1) IAA binds to a receptor protein on the cell surface membrane
2) IAA stimulates ATPase proton pumps to pump H+ from the cytoplasm into the cell wall, acidifying the cell walls and lowering it’s pH
3) This activates proteins knows as expansins which losen bonds between cellulose and microfibrils
4) Potassium ion channels are also stimulated to open leasing to an increase in potassium ion concentration in the cytoplasm, decreasing the water potential of the cytoplasm
5) This causes the cell to absorb water by osmosis which is then stored in the vacuole
6) Internal pressure of the cell increases causing the cell wall to stretch
7) elongating the cell
The role of iAA in elongation of cells simple
1) IAA binds to receptor
2) ATPase pumps protons into cell wall
3) Bonds between cellulose microfibrils are loosened
4) Potassium ion channel opens and K+ enter cytoplasm
5) Water moves down a water potential gradient and enters cytoplasm
Describe phototropismq
Affects shoots and top of stem
Positive phototropism = shoot grows towards light
How does IAA affect phototropism
Conc of IAA not equal on both sides of root or shoot = uneven growth
High conc of IAA = greater rate of elongation
Describe how IAA affects shaded side of plant
1) IAA molecules evenly distributed
2) IAA molecules move towards the shaded side
3) IAA stimulates cell alongation causing the shaded side to grow at a faster rate
What does gravi tropism affect
Roots
Roots grow towards gravity = positive gravitropism
IAA concentrations on gravitropism
High conc of IAA = lower rate of cell elongation
How do some plants detect gravity
Columellar cells near root tip are heavy as they contain amyloplasts
Amyloplasts densely packed with starch so sink to bottom of cell
When root moves from vertical ro horizontal these organelles fall to where the bottom of the cell is
How does iaa work in gracitropism
IAA actively transported to region in root tip where amyloplasts have sunk
Larger conc of IAA at lower side of root inhibit cell elongation
Lower side grows at slower rate
What are taxis and kinesis
Simple responses that enable mobile organisms to stay in a favourable environment
What type of response is kinesis
Non-directional response to a stimulus
