Krug P J, Manzi A E
Biol Bull. 1999 Aug;197(1):94-103. doi: 10.2307/1543000.
Larvae of the specialist marine herbivore Alderia modesta (Opisthobranchia: Ascoglossa) metamorphose in response to a chemical settlement cue from the alga Vaucheria longicaulis, the obligate adult prey. Bioactivity coeluted with both high and low molecular weight carbohydrates in solution, and with insoluble high molecular weight carbohydrates associated with the algal cell wall. Larvae metamorphosed in response to water conditioned by V. longicaulis, as well as to frozen and homogenized algal tissue. The inducer was efficiently extracted from the algae with boiling water, but after all soluble activity was extracted, residual tissue still induced larval settlement. Ethanol precipitation of a boiled-water extract followed by gel filtration chromatography showed that the precipitate contained carbohydrates of >100,000 Da molecular weight, while the supernatant contained only low molecular weight carbohydrates (<2,000 Da); in both cases all activity was associated with the carbohydrate peak. An aqueous-insoluble 4% NaOH extract was chromatographed in 7 M urea to yield a bioactive high molecular weight carbohydrate peak. Activity was not affected by proteinase K or mild acid hydrolysis, but was significantly decreased by periodate treatment. The results indicate that larvae of A. modesta metamorphose in response to both water-soluble and surface-associated carbohydrates of V. longicaulis, and that the soluble cue exists as both high and low molecular weight isoforms.
专性海洋食草动物适度阿尔代海蛞蝓（裸鳃目：枝鳃亚目）的幼虫会因来自其唯一的成年猎物——长茎无隔藻的化学附着信号而发生变态。生物活性在溶液中与高分子量和低分子量碳水化合物共同洗脱，并与与藻类细胞壁相关的不溶性高分子量碳水化合物共同洗脱。幼虫会对经长茎无隔藻处理过的水以及冷冻和匀浆的藻类组织产生变态反应。诱导物能用沸水从藻类中有效提取，但在所有可溶性活性被提取后，残留组织仍能诱导幼虫附着。对沸水提取物进行乙醇沉淀，然后进行凝胶过滤色谱分析，结果表明沉淀物中含有分子量大于100,000道尔顿的碳水化合物，而上清液中仅含有低分子量碳水化合物（<2,000道尔顿）；在这两种情况下，所有活性都与碳水化合物峰相关。将一种水不溶性的4%氢氧化钠提取物在7 M尿素中进行色谱分析，得到一个具有生物活性的高分子量碳水化合物峰。活性不受蛋白酶K或温和酸水解的影响，但经高碘酸盐处理后显著降低。结果表明，适度阿尔代海蛞蝓的幼虫会对长茎无隔藻的水溶性和表面相关碳水化合物产生变态反应，且可溶性信号以高分子量和低分子量异构体的形式存在。
