根虫瘟霉不同菌株对小菜蛾幼虫血淋巴酚氧化酶原的激活作用

在对小菜蛾Plutella xylostella幼虫血淋巴酚氧化酶原的存在部位及免疫激活作用特点研究的基础上，比较了根虫瘟霉Zoophthora radicans不同菌株对酚氧化酶原激活系统的免疫激化及防御作用的差异。研究发现， 酚氧化酶原主要位于小菜蛾幼虫血细胞膜及血细胞裂解液中，极少存在于血浆中。在免疫激活剂昆布多糖存在下，分别测得小菜蛾幼虫血细胞碎片、血细胞裂解液和血浆的酚氧化酶活性为26.80 U，16.68 U和2.53 U。酚氧化酶原显著地受血浆和昆布多糖同时存在的激活，但两者单独存在时对酚氧化酶原的激活作用较弱。根虫瘟霉菌丝裂解液对酚氧化酶原有不同程度的激活作用，其激活作用在有血浆存在时显著增强，其酚氧化酶活性可提高2.9～3.4倍。各菌株间对酚氧化酶原的激活作用则以ARSEF1342菌株最强，ARSEF2699和F99101菌株次之，ARSEF1100菌株最弱。被激活的酚氧化酶可粘附于根虫瘟霉菌丝上并能产生黑化反应，各菌株间酚氧化酶粘附于ARSEF1342菌株的能力最强，粘附于ARSEF2699和F99101菌株的次之，粘附于ARSEF1100菌株的最弱。但酚氧化酶粘附于昆布多糖的能力显著强于各虫霉菌株，表明各菌株在一定程度上能逃避寄主的免疫识别；各菌株激活酚氧化酶原及酚氧化酶粘附于菌株强弱，与对小菜蛾毒力呈负相关性，表明高毒力菌株具有易逃避寄主免疫识别的趋向。

Activation of prophenoloxidase by Zoophthora radicans isolates from different hosts in hemolymph of Plutella xylostella larvae (Lepidoptera:Plutellidae)

The activation of prophenoloxidase (ProPO) in the hemolymph of the diamondback moth Plutella xylostella larvae against infection of Zoophthora radicans isolates from different hosts was investigated. The ProPO was found primarily on the membrane or inside host hemocytes, but less in plasma. When laminarin as an immune activator was present, phenoloxidase (PO) activities in cell debris, hemocyte lysate solution and plasma were measured as 26.80, 16.68, and 2.53 U, respectively. The ProPO was significantly activated by laminarin present in the plasma due to a much higher PO activity than that when the laminarin or the plasma was tested alone. The ProPO activity increased by 2.9-3.4-fold when the lysate of Z. radicans mycelia was present in host plasma. Among the four isolates tested, the PO activity was highest in ARSEF1342, medium in ARSEF2699 or F99101, but lowest in ARSEF1100. Furthermore, the activated PO in the mycelia of Z. radicans caused melanism, an evidence of the immune defending response of hosts to fungal infection. The PO activity was triggered most conspicuously by ARSEF1342 than by ARSEF2699 or F99101, but very weakly in ARSEF1100. The fact of the more attachment of the PO to the laminarin than to Z. radicans isolates revealed a trend that the fungal pathogen may to some extent evade from the host immune response. This was further revealed by the correlation between the virulence of different isolates against P. xylostella and the ProPO activation by the isolates or the following PO activities in the lysates of their mycelia.