9.3 Chemical Control In Plants Flashcards
Role of auxins
Apical dominance
Tropism and differential growth
Root growth
(Seeds develop to fruits)
(Inhibition of lateral buds)
Role of gibberellins
Stem and leaf elongation
(Breaking dormancy in cells)
Encouraging embryo growth
Role of cytokinins
Promote auxiliary lateral bud development
Antagonise auxin
Part 1 of action of IAA
1) IAA binds to cell surface receptor of plant cell
2) receptor is bound to H+ pump which activates
3) H+ pumped into intercell membrane soace
Part 2 of action of IAA
4) disrupts H bonds causing microfibres to slide past each other and weaken
5) water enters cell by osmosis
6) cell expands and elongates
Part 3) action of IAA
7) IAA breaks down inactivating pump
8) pH returns to normal
9) cellulose reforms H binds and becomes rigid
Mechanism of apical dominance
Auxins released by shoots inhibits lateral buds
Acts antagonistically with cytokinin which leads to development of lateral buds
As plant grows first shoot moves away so cytokinin causes lateral buds to develop lower down
If apical bud is removed cytokinin in full effect so single stem branches to lateral buds
Why is it called growth substances and not plant hormones
Not released from glands
Don’t travel in blood
But they are chemical messengers
(Plants don’t have hormones)
Phototropism in shoots
IAA released from shoot tip and travels down the shoot
IAA moved to shaded side so high conc on shaded side than sunny side
High IAA cinc causes cells to elongate more on shaded side so bend towards light
Positive phototropism
Role of geotropism and roots in plants
Anchorage
Absorb water and ions
Role of hydrotropism in roots
Positive hydrotropism
Turgid structure
Metabolic process
LD reaction and photolysis
Geotropism
Higher concentration of IAA on lower Side of roots
Inhibits cell elongation on this side
Cells on upper side elongate down towards gravity
Type of light during day
red light
Type of light during night
Far red light
Is transfer to Pr of to Pfr faster
Pr-Pfr is faster
(During day)
