9水杨酸Salicylates

水杨酸类（salicylates）药物包括阿司匹林和水杨酸钠（sodium salicylate）等，由于水杨酸本身刺激性强，仅作为抗真菌药和角质溶解药，而阿司匹林则应用广泛。

水杨酸 Salicylates

• Discovery of SAs
  • Hippocrates wrote about the use of willow to relieve pain ~ 2400 years ago
  • 1979
    • White showed that pretreatment of a leaf with aspirin or SA conferred resistance to tobacco mosaic virus (TMV)
  • 1987
    • Endogenous SA was shown to be responsible for heat production in Arum lily flowers
  • 1990
    • SA was shown to be an endogenoussignal in defense responses
• Types and Structure of SAs
• Biosynthesis of SAs
  • There are two pathways for SA synthesis, via ICS and PAL
    • A small amount of SA is derived from cinnamic acid produced by PAL in the cytoplasm
    • The major route for biosynthesis of SA (up to 95% of total) takes place in the chloroplast. One of the key enzymes is ICS, isochorismate synthase
• Regulation and Metabolism
  • SA is modified and conjugated to active and inactive compounds
  • Most SA is synthesized in the chloroplast, conjugated in the cytoplasm and sequestered in the vacuole
• Perception and signaling
  • SA induces an enormous transcriptional response
  • PR genes are pathogenesis related genes, and are involved in defense responses
  • Signaling pathway
    • NPR1 binds TGA transcription factors and promotes DNA binding
    • In the nucleus, SA-activated NPR1 promotes transcription
    • WRKYs are a large family of transcription factors
• Physiological Function
  • Responses to pathogens
    • Recognition
    • Local and hypersensitive response
    • Systemic acquired resistance
  • Cross-talk
  • Other functions
    • Abiotic stress
    • Thermogenesis