ABA

Interactions between ABA and other hormones that are antagonistic to ABA


Abscisic Acid hormone
- controls seedling's vigour
- promotes reserve synthesis and late-embryogenesis abundant (LEA) proteins (for the protection of water stress)
- accumulation of dessication protectants
- promotes seed dormancy
- inhibit precocious germination (vivipary)

Evidence
1) embryo culture - addition of ABA inhibit germination and promoted reserve deposition
2) vivipary - Red mangrove reduced sensitivity to high [ABA]
3) preharvesting - germination on parent plant prior to harvesting, eg. cereals, again, insensitive to high [ABA]

*NOTE: sprouting susceptible - they like to sprout no matter what so insensitive to ABA, transcription factor decreased at maturity, eg. cereals
sprouting resistant - don't want to sprout so SENSITIVE to ABA, ABI3/VPI1 transcription factor levels maintained throughout

Lec 4
response mutants - insensitivity to ABA, defective ABA signaling pathway
e.g. vp1 (all lowercase when naming mutants, all upper case when naming GENES, eg. VP1 gene) in maize, abi3 in arabidopsis (green, less dormant, less reserve, dessication/drying-intolerant, matures prematurely)

ABI3/VP1 genes are transcription factors, binds with FUS3, LEC1 transcription factors and they all bind to RY cis promoter to control maturation

ABRE - ABA-ResponsiveElements (promoter element, sequence in genes)

ABA/GA ratio (ABA - sleep pill and GA - wake up pill are antagonistic)
These GAs induce a developmental program that leads to vivipary
in the absence of normal amounts of ABA

A reduction of GAs re-establishes an ABA/GA ratio appropriate for suppression
of germination and induction of maturation.

Mod 6, 7
Sprouting leads to damage due to premature hydrolysis of grain reserves –
hydrolytic enzymes associated with post-germinative reserve mobilization
degrade starch & protein of grain

When malting process is terminated, malted grain consists of
friable endosperm containing:
High amounts of enzymes, e.g. α-amylase, which will later
participate in the hydrolysis of the starch to produce sugars
for fermentation
Altered protein & various other chemicals (quality of final product)
Pre-harvest sprouted grain is unacceptable to the malting industry!