链格孢Alternaria alternata侵染导致瓜类幼苗白化的机制

用分离自无症状瓜类植物的27株链格孢属Alternaria真菌接种黄瓜,有14株引起了黄瓜幼苗的白化,这些菌株均属于链格孢A. alternata。为揭示A. alternata引起黄瓜幼苗白化的机制,对代表菌株5F29经固体发酵后提取其次级代谢产物,将粗提物按一定量混入基质进行盆栽实验。结果表明,黄瓜、丝瓜和甜瓜对该粗提物敏感,出现白化苗;小白菜和辣椒对粗提物不敏感,生长正常。植物幼苗用粗提物处理的结果与用产生菌接种的结果相一致。粗提物经硅胶柱层析、葡聚糖凝胶柱层析及高效液相色谱（HPLC）等方法分离纯化得到一种活性化合物,经测定该化合物引起黄瓜幼苗白化的最低浓度为12.5μmol/L。该化合物在此浓度下可引起黄瓜幼苗生长点白化,在15μmol/L的浓度下可引起黄瓜幼苗大部分组织白化,致使幼苗很快死亡。应用核磁共振和质谱技术,确定了该化合物的结构,鉴定为一种植物毒素——腾毒素（tentoxin）。研究结果揭示了A. alternata引起瓜类幼苗白化的机制以及不同植物对于腾毒素的不同敏感性。

Mechanism of cucurbit seedling albinism caused by Alternaria alternata

Cucumber seedlings were inoculated with 27 strains of Alternaria isolated from asymptomatic cucurbit plants. There were 14 strains causing albinism of cucumber seedlings and all of them belong to A. alternata. The secondary metabolites of a representative strain 5F29 were extracted after solid fermentation, and the crude extract was mixed into the substrate in an appropriate amount for pot experiments. The results showed that cucumber (Cucumis sativus), sponge gourd (Luffa cylindrica) and melon (Cucumis melo) were sensitive to the crude extract, and albino seedlings appeared; pak choi (Brassica rapa var. chinensis) and pepper (Capsicum annuum) were not sensitive to the crude extract, showing normal growth. The result of plant seedlings treated with the crude extract were consistent with that inoculated with the fungal mycelia. An active compound was separated and purified by chromatography on silica gel column, Sephadex LH-20 column, and high performance liquid chromatography. The minimum concentration of the compound causing cucumber seedling albinism was determined to be 12.5μmol/L. At this concentration, the compound caused albinism of cucumber seedling growth point, and at a concentration of 15μmol/L, it resulted in albinism of most tissues of cucumber seedlings, rendering quick death of the seedlings. Nuclear magnetic resonance and mass spectrometry techniques were used to determine the structure of the compound which was identified as a phytotoxin—tentoxin. The results revealed the mechanism of A. alternata-caused albinism of cucurbit seedlings and different sensitivity of different plant species to tentoxin.