Plant Growth Factors Flashcards
What changes do plants respond to
Light - shoots grow towards light, for photosynthesis
Gravity- need to be firmly anchored in soil, roots grow in direction of its pull
Water - roots grow towards water to absorb for photosynthesis
What is IAA? And what does it do
It’s a plant growth factor
It controls plant elongation
Describe the response of the shoots of flowering plants to unilateral light
Cells in the top of the shoot produce IAA, which is then transported down the shoot
IAA is initially transported evenly throughout all regions as it begins to move down the shoot
Light causes the movement of IAA from the light side to the shaded side of the shoot
Greater concentration of IAA builds up on the shaded side of the shoot than on the light side
As IAA causes elongation of shoot cells and there is greater concentration of IAA on the shaded side of the shoot, the cells on this side elongate more
The shaded side of the shoot elongates faster than the light side, causing the shoot time to bend towards the light
What does a high concentration of IAA in shoots inhibit
Cell elongation in roots
Describe gravitropism in plants , response of horizontally growing root to gravity
Cells in tip of the root produce IAA which is then transported along the root
The IAA is initially transported to all sides of the root
Gravity influences the movement of IAA from the upper side to the lower side of the root
A greater concentration of IAA builds up on the lower side of the root than the upper side
As IAA inhibits the elongation of root cells and there is a greater concentration of IAA on the lower side, the cells on this side elongate less than those on the upper side
The relatively greater elongation of cells on the upper side compared to lower side causes the root to bend downwards towards gravity
What happens in shoots of the IAA concentration is greater in the lower side
It increase cell elongation and causes this side to elongate more then the upper side, therefore growing away from gravity
What effect does IAA have on plant cells
Increasing ability to stretch of their cell walls
As cell natures they develop rigidity
How can we explain how IAA increases the plasticity of cells ?
Acid growth hypothesis
Active transport of hydrogen ions from the cytoplasm into spaces in the cell wall causing the cell wall to become more plastic allowing the cell to elongate by expansion
