Plant hormones, coordination and the brain Flashcards
What are plant growth factors and where are they produced?
Chemicals that regulate plant growth response to directional stimuli.
Produced in plant growing regions (apical meristems).
Diffuse from cell to cell / phloem mass transport.
What is a phytochrome?
A plant photoreceptor with bilin chromophore group. Converts between biologically inactive Pr and biologically active Pfr.
What effect does phytochrome have on plants?
They affect growth and development. They regulate aspects of development such as flowering and synthesis of chlorophyll.
What is photomorphogenesis?
The pattern of plant growth and development determined by light intensity.
How does phytochrome control photomorphogenesis?
Transition from Pr to Pfr controls localisation of proteins within cells, transcription of certain genes, phosphorylation of proteins.
It therefore affects germination, circadian rhythm and flowering.
How does phytochrome control flowering?
Pr absorbs red light and converts to Pfr, which stimulates flowering (signifies that light intensity is great enough for photosynthesis)
How does phytochrome affect gene transcription?
The Pfr can enter the nucleus where it can bind to transcription factors like PIF (phytochrome inhibiting factor) which activates the transcription of genes such as those involved in the synthesis of chloroplast proteins like RuBisCo.
What is Indole Acetic Acid (IAA)?
A type of auxin which is mainly produced at growing plant tips which is used to promote cell growth and elongation.
List the functions of auxins in plants
-Involved in trophic responses e.g. IAA
-Control cell elongation
-Suppress lateral buds to maintain apical dominance
-Promote root growth e.g. in rooting powders
What is apical dominance?
When during the growth of the shoot, the growth of side shoots doesn’t take place. Maintained by the action of auxin, abscisic acid and cytokinins.
How is germination stimulated?
- Seed absorbs water, activating embryo to secrete gibberellins.
- Gibberellins diffuse to aleurone layer, which produces amylase.
- Amylase diffuses to endosperm layer to hydrolyse starch.
- Hexose sugars act as respiratory substrate to produce ATP.
How does IAA affect gene transcription?
Certain transcription factors related to auxin-controlled genes are in the nucleus. They’re typically blocked by other proteins from enhancing transcription. When auxin levels rise, these proteins are broken down and the transcription factors can promote transcription.
Explain why shoots show positive phototropism.
- Indoleactic acid diffuses to shaded side of shoot tip.
- IAA diffuses down shaded side and causes active transport of H+ ions into cell wall.
- Disruption of H-bonds between cellulose molecules and action of expansions make cells more permeable to water.
- Cells on shaded side elongate faster due to higher turgor pressure.
- Shoot bends towards the light.
Explain why roots show positive gravitropism
- Gravity causes IAA to accumulate on lower side of the root.
- IAA inhibits elongation of root cells.
- Cells on upper side of the root elongate faster, so the root tip bends downwards.
What are gibberellins?
Plant hormones that control stem elongation, trigger the growth of the pollen tube during fertilization and stimulate the mobilization of food storage reserves during seed germination.