Chapter 23 Abscisic Acid Questions and Answers

Chapter 23 Abscisic Acid Questions and Answers Location of abscisic acid present in all parts of plant Bioassays 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) Previous Play Next Rewind 10 seconds Move forward 10 seconds Unmute 0:00 / 0:15 Full screen Brainpower Read More Basic facts about abscisic acid 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... vascular tissue, especially phloem First effect of ABA Induces dormancy of seeds and buds (or quiescence) Second effect of ABA Increases desiccation tolerance of embryo (via protective proteins) and increases storage proteins Third effect of ABA Stomatal closure (ABA synthesized in roots in drying soil, results in signal to decrease transpiration) Fourth effect of ABA senescence of leaves (independently of ethene) Fifth effect of ABA 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 High [ABA] leads to an increase in the production of ethene ABA redistribution is affected by... 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 - increased pH of xylem sap (more alkaline); - increased pH of apoplast of mesophyll; - increased [ABA-] in apoplast and xylem Dehydration - ↓ pH of cytosol in the mesophyll (acidic); - increased [ABA-H] escaping from cytosol Mechanisms by which ABA works involve: membrane effects; gene transcription Membrane effects (regulating ion channels) ABA - increase [Ca2+] in the cytosol and increase in the pH of the cytosol which affects ion channels and H+-pumps Gene transcription (via various signal transduction pathways)