4脱落酸 Abscisic

脱落酸(abscisic acid,ABA) 别名:天然脱落酸,2-顺式,4-反式-5-(1-羟基-4-氧代-2,6,6-三甲基-2-环己烯-1-基)-3-甲基-2,4-戌二烯酸 (S)-5-(1-Hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3..

脱落酸 Abscisic Acid（ABA）

• Discovery of ABA
  • Abscisic acid (ABA) was identified as one compound that promotes leaf abscission and bud dormancy
    • Abscisin
      • 1961,1963
    • Dormin
      • 1964
    • ABA
      • 1967
• Types and Structure of ABA
  • cis-ABA
    • Naturally occurring active form
  • trans-ABA
    • Inactive, but interconvertible with active (cis) form
  • These two forms can change into each other
• Biosynthesis of ABA
  • ABA is synthesized in the plastid and cytoplasm and is derived from zeaxanthin, a plant pigment
  • Core enzyme
    • ZEP：玉米黄素环氧化酶
    • NCED： 双加氧酶，限速酶
    • ABA2：醇脱氢酶
    • VAAO3：醛加氧酶
  • Synthetic pathway
• Regulation and Metabolism of ABA
  • Inactivation pathway
  • Rehydration of vegetative tissues causes ABA levels to drop
    • Leaf detached to initiation drying at time ZERO
    • ABA accumulates
    • Rehydration by immersion in water
    • ABA is irreversibly deactivated by conversion to phaseic acid
  • ABA can be reversibly inactivated by glucosylation
    • ABA- glucosyl ester (ABA-GE) is an inactive storage and transfer form
  • ABA accumulation and homeostasis are tightly controlled
    • Synthesis
      • Water stress Developmental signals
    • Degradation or Inactivation
      • Rehydration Developmental signals
• Transport of ABA
  • ABA movement – between organs and cells
    • ABA translocation and root hydraulic signals may be involved in signaling from root to shoot
  • Characteristics for ABA movement
    • ABA is a weak acid and exists in charged and uncharged forms
      • As a weak acid, abscisic acid is a charged anion (ABA-) in the cytoplasm (pH 7)
      • In the more acidic cell wall (pH 5.5) some is uncharged (ABAH). This presumably enhances the movement of ABA into but not out of cells
• Perception and signaling
  • Core components
    • PYR/RCAR receptors
    • PP2C Protein phosphatases (including ABI1)
    • Protein kinases (including SnRK2s and CDPKs)
  • Pathway
    • The PYR/RCAR ABA receptors are necessary for ABA responses
    • PYR/RCAR receptors bind ABA in a complex with ABI1 or other PP2Cs
    • PP2Cs interfere with the action of SnRK2 protein kinases
    • A major output of ABA signaling is changes in transcription patterns. Many of the transcriptionally upregulated genes have functions in osmoprotection
• Physiological Function
  • Guard cell responses
    • Guard cells are the portals through which CO2 enters and H2O exits
      • Osmotic movement of water controls guard cell turgor
      • Ion channels and pumps control the movement of guard cells
      • ABA triggers the movement of ions out of the cell
    • Calcium dependent protein kinases contribute to guard cell movement
    • Protein kinases and phosphatases are critical for guard cell responses
  • Root growth
    • Water stress and ABA promote root growth at the expense of shoot growth
    • ABA promotes root elongation and suppresses branching
  • Vegetative dehydration responses and osmoprotectants
  • Biotic stress responses
    • ABA induces genes that protect cells from desiccation damage
  • Drought-tolerant plants