Presentation on theme: "Roles in Seed Dormancy and Stomatal Closure"— Presentation transcript:
1Roles in Seed Dormancy and Stomatal Closure Biol 352 Lecture 9Abscisic Acid:Roles in Seed Dormancy and Stomatal ClosureFebruary 5, 2007
2Review: ethylene Ethylene is a gaseous plant hormone. Precursor: amino acid methionine; immediate precursor: ACC.Key enzymes for biosynthesis: ACC synthase, ACC oxidase.Ethylene functions: fruit ripening, triple response, abscission, flower senescence, root hair development, etc.Two-component signalling system in ethylene signal transduction.
3Lecture Outline: Structure of ABA Biosynthesis of ABA Function of ABA: seed dormancy, water stress responseABA signalling in stomatal guard cellsSummary
4Learning Objectives: Reading: Define the key enzymes in ABA biosynthesisDetermine the roles of ABA in seed germination/dormancyExplain ABA signalling in stomatal guard cellsReading:4th Ed, Plant Physiology, Taiz & Zeiger, Chapter 23: p(3rd Ed, Plant Physiology, Taiz & Zeiger, Chapter 23: p )
5ABA: a Dormin Naturally occurring active form Inactive in stomatal closure\figures\ch23\pp23010.jpgInactive, but interconvertible with active cis form
6Abscisic acid (ABA): Is not the primary hormone for abscission. Is the primary hormone responsible for seed dormancy.Is the major stress hormone.Is the only member of its class.Is a 15-carbon compound resembling the terminal portion of some carotenoid molecules.The (s)-cis-ABA is the naturally occurring active form.
7ABA Biosynthesis:Synthesized in almost all cells that contain chloroplasts or amyloplasts.Key intermediate: Violaxanthin (C40)Key enzymes:Zeaxanthin epoxidase (ZEP), ABA19-cis-epoxycarotenoid dioxygenase (NCED), VP14ABA-aldehyde oxidase, ABA3
11Functions of ABA:Seed dormancyDrought stress response
12Seed germination: the resumption of growth of the embryo of the mature seed. …normally requires water, oxygen, suitable temperature, absence of inhibitory substancesSeed dormancy: a viable seed will not germinate even if all the necessary environmental conditions for growth are satisfied.
13Cause of DormancyCoat-imposed dormancy: dormancy imposed in the embryo by the seed coat and other enclosing tissues, such as endosperm, pericarp, or extrafloral organs.Embryo dormancy: a dormancy that is intrinsic to the embryo and is not due to any influence of the seed coat or other surrounding tissues.
14Seed Dormancy: Seed dormancy is controlled by the ratio of ABA to GA. ABA inhibits GA-induced enzyme production.
15Precocious germination in the ABA-deficient vp14 mutant of maize VP14 encodes NCED, 9-cis-epoxycarotenoid dioxygenase\figures\ch23\pp23030.jpg
21ABA Signaling in Stomatal Guard Cells [Ca2+]pHK+outK+inH+ pump\figures\ch23\pp23120.jpgPromotestomatal closingPreventstomatal opening
22Summary:ABA is the major hormone responsible for seed dormancy and water stress response.Key enzymes for biosynthesis: ZEP (ABA1), NCED (VP14), and ABA-aldehyde oxidase (ABA3).ABA antagonizes the action of GA in seed germination.ABA controls stomatal guard cell closure/opening.ABA signaling in stomatal guard cells: Ca2+, K+, H+.