Answers
Location of abscisic acid - answer present in all parts of plant
Bioassays - answer stomatal closure; inhibition of germination, coleoptile growth,
and amylase synthesis in seeds; various gene expression assays-- physical methods
are better, though (immunoassays, gas chromatography if the ABA is purified first,
HPLC)
Basic facts about abscisic acid - answer synthesized in all cells with plastids;
synthesized from a carotenoid intermediate (via terpenoid pathway); "growth inhibitor",
(increases dormancy); "stress hormone" (especially water stress, which leads to
stomata closure)
Abscisic acid is transported in... - answer vascular tissue, especially phloem
First effect of ABA - answer Induces dormancy of seeds and buds (or quiescence)
Second effect of ABA - answer Increases desiccation tolerance of embryo (via
protective proteins) and increases storage proteins
Third effect of ABA - answer Stomatal closure (ABA synthesized in roots in drying
soil, results in signal to decrease transpiration)
Fourth effect of ABA - answer senescence of leaves (independently of ethene)
Fifth effect of ABA - answer increased root growth (a lot, via suppressing ethene in
root) and decreased shoot growth (a bit) IF plant is water stressed (leads to an
increased root-to-shoot biomass ratio)
Sixth effect of ABA - answer High [ABA] leads to an increase in the production of
ethene
ABA redistribution is affected by... - answer pH; anion trap concept: ABA gets
trapped in alkaline (higher-pH) compartments because -> ABA- (not ABA-H) (recall: ions
cannot diffuse across membranes)
Water stress - answer -> increased pH of xylem sap (more alkaline); -> increased pH
of apoplast of mesophyll; -> increased [ABA-] in apoplast and xylem
Dehydration - answer -> ↓ pH of cytosol in the mesophyll (acidic); -> increased [ABA-
H] escaping from cytosol