| Inducible defenses contian a combination of responses, such as structural changes and synthesis of chemical, that it is arising under the stimulus of injury (wounding, mechanical pressure, attack by insects or microorganisms, physiological disturbances). The anatomical effects of methyl jasmonate (MJ) and ethylene, a potent inducer of certain plant defenses, were compared with normally structure of mature Pinus armandii.1. In Pinus armandii stem, phloem resin ducts, phloem rays resin duct, xylem rays resin duct and xylem axial resin canalwere found in the secondary structure, cortical resin duct and primary xylem resin ducts in primary structure. Resin ducts were composed of a layer of epithelial cells and 1-2 layers of sheath cells. Resin ducts in the secondary xylem mostly distribute in the late-earlywood, where constitutive resin duct occur frequently.2. Pinus armandii defense system against bark beetles and their associated pathogenic fungi can be classified as constitutive and induced. This complex system include:Polyphenolic parenchyma cells, ray cells, rays resin duct, phloem resin duct, xylem axial resin duct. Those defense element are under different regulation and coordinated to achieve optimal effect. Constitutive defenses are made of preformed phloem resin duct, xylem resin duct, and extensive compression of sieve cells because of the enlargement of phloem parenchyma cell. Wounding or inducing of exogenous MJ and ethylene could result in traumatic resin duct, as a induced defense response. Furthermore, the compression of sieve cells are notable and early.3. Methyl jasmonate, ethylene can induce similar defense as wounding in Pinus armandii, but the formation of traumatic resin duct required different time. Ethylene needs 30 days, methyl jasmonate and wound to cambium needs 45 days, wound to the phloem will need 60 days. Ethylene inhibitor 1-MCP can block the induced defense, suggesting that MJ and ethylene were the key signal for inducible defense mechanisms.
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