Lecture 10 Flashcards
Features for chemical signalling (4)
Perception of environmental change
Signals work on an interactive signal-transduction cascade
Hormones act as a primary signal
Secondary messengers follow hormones
Categories of plant signalling mechanisms (5)
Environmental perception Plant hormones Secondary messengers Genetic transcription & translation Physiological regulation
Major hormones (6)
Auxin (division/expansion/growth/vascular formation/suppress leaf senescence)
Gibberellin (division/elongation/growth/induce germination/stimulate flowering/overcome dormancy)
Cytokinen (division/shoot formation/greening leaves/suppresses senescence + root growth)
Abscisic acid (ABA) (promote dormancy/close stomata/slows division/suppresses growth)
Ethylene (promote ripening/abscission/senescence)
Brassinosteroids (growth regulation/xylem maturation/branching/germination)
Minor hormones (2)
Salicylic acid
Jasmonic acid
Hormone characteristics (5)
Act as chemical messengers
Physiological/molecular response occurring in the same or distant tissues
Active in low concentrations
Indice specific responses
Act w other hormones (synergistically or antagonistically)
Regulation of hormone effect
Has only one active pool, two inactive pools for regulation (must travel and be transported a lot)
Also relies on tissue sensitivity before signal to develop is sent out
What is auxin, where does it originate from? What is the most common form? How does it flow?
Auxin refers to a group of molecules the most common being Indole Acetic Acid (IAA)
It originates from the leaf primordia, SAM and RAM
It flows from the site of synthesis down to the base of the plant (polar movement
Auxin functions (9)
Promote cell division/expansion Induce vascular tissue formation Suppress leaf senescence Delays leaf abscission Increase wall extensibility An intermediary in phototropism/gravitropism Inhibit lateral stem formation Promote lateral/adventitious root formation Determines pattern of leaf emergence
Two types of auxins
Native
Synthetic
Transport mechanisms (2)
Polar transport (basipetal or acropetal) (in vascular parenchyma) Nonpolar transport (in sieve tube elements)
Auxin polar transportation
1) what forms (2) do auxin enter as and where? What are the influx carriers?
2) what form does auxin exit? What are the efflux carriers?
1)
IAAH in vascular parenchyma by passive diffusion
IAA- in vascular parenchyma by active co-transport
Influx carriers: AUX1 proteins
2)
IAA- exits
Efflux carriers: PIN proteins
What are PIN proteins?
Group of proteins that mediate transport of IAA from shoot to root
PIN3 redirects laterally diffused auxin
Transports auxin to where it can be sequestered/stores
Can be recycled or remade by the Golgi
What is AuxRE?
Binding sites for Auxin Response Factor (ARF)
Protein-protein interaction domains
What regulates AuxRE? How is this regulator inhibited?
Regulated by AUX/IAA repressors
Repressors are inhibited (essentially pathway is activated again) through auxin-dependent degradation (ubiquitin lipase + auxin)
Auxin promoting lateral root formation process
Pericycle cells begin undergoing anticlinal divisions
Form lateral root primordia
Lateral root primordia divides periclinally
Make an inner/outer layer
Emergence of primary root
What is KRP2? What does it do and how is it regulated?
KRP2 is a protein that inhibits cell cycle progression by inhibiting cyclin dependent kinases
KRP2 + CDKA-Cyclin D inactivates cyclin
Downregulated by auxin
How is the positioning of a lateral root established?
Polarized PIN1 proteins direct where auxin gradients form -> auxin gradient location decides where lateral root primordia forms
GNOM + Polar Auxin Transport + PIN Proteins
GNOM regulates formation of vesicles during membrane trafficking
Actin filaments pull vesicles for transport
PIN proteins use these vesicles pulled by/along actin to move from endosomal compartments to the plasma membrane
What is gravitropism? What are the types (2)?
Gravitropism is where plants grow in response/respect to gravity
Types:
Positive (roots grow down into the soil)
Negative (shoots grow up from the soil)
What is used to sense gravity for gravitropism?
The root cap contain many columella that have amyloplasts in statocytes (called statoliths) that sense gravity
(If the root cap is removed the root cannot sense gravity/which direction to grow in)
What happens when Root position is changed? (Vertical vs. Horizontal)
Vertical root position has symmetrical auxin distribution moving back on both sides
Horizontal Root position has redistribution of PIN3 so auxin moves preferentially along the bottom side (inhibits elongation zones on the bottom so growing only occurs on the side)
In phototropism what controls one sided elongation? Why does this arise?
GSL8 (a callose synthase) control the deposition of plasmodesmata -> ie. closes PDs on the side that has more sunlight to prevent growth
Arise depending on where the sun is:
Directly overhead (no need for GSL8 because there is even auxin distribution)
At an angle (need GSL8 so auxin concentrates on the side that lacks sun to promote its growth toward the sun)
What is Apical dominance? How does it work?
Apical dominance is where the terminal bud (top/shoot tip) controls (suppresses) auxiliary bud growth
How it works:
If present = auxiliary growth is inhibited by auxin that flows down stem
If absent = auxiliary bud grows due to lack of inhibition (lateral buds are now inhibited)
What is Abscisic Acid? Where does it originate from and where is it found?
Is a hormone that slows/stops growth and development (inhibitory molecule)
Originates in plastids
Found in all tissues
Abscisic acid Function (7)
Slows growth during stress Signals stress acclimation Closes stomata Promotes seed maturation/seed storage/protein synthesis/seed desiccation tolerance Promotes dormancy in seeds/buds Inhibits advanced germination Promotes senescence of stressed leaves
Ca+2-dependent signal transduction pathway in Stomatal Closure
ABA binds to a Receptor on a guard cell membrane Initiates Ca influx Ca binds to CaR Open anion efflux channels Membrane depolarize K efflux channels open Loss of osmotica Loss of turgor GCs deflate Stomata close
How does ABA maintain dormancy?
Is abundant when environmental conditions are unfavourable
Only removed from seed coat after heavy moisture
Types of cytokinin (2) Where do they originate and where are they transported to afterwards?
Kinetin (synthetic)
Zeatin (naturally occurring)
They originate in root meristems and are transported to the shoot
Function of cytokinins
Delay lead senescence/promote greening
Increase sink strength for nutrients
Accelerate cell cycle (promote D-type cyclin)
Promote shoot/leaf growth (accelerate cell division/expansion)
Suppresses root growth
Cytokinin va ABA release depending on environmental conditions
High resources: more cytokinin release = root suppression, shoot growth
Low resources: more ABA release = shoot suppression
How to plant pathogens manipulate cytokinins to their benefit?
Pathogens insert their genes into the T-DNA of the host plant (form a recombinant plastid)
The T-DNA contains cytokinin synthesis genes and when injected with foreign genes causes the over-expression of cytokinin synthesis
Over-expression tricks plant into believing it has a sink to which it should send resources to (forms tumour like growth that pathogens use to their advantage)
