Hybridization in North American Asclepias. II. Flavonoid Evidence
Hybridization in North American Asclepias. II. Flavonoid Evidence
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北美马利筋的杂交。
DOI：
10.2307/2418978
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发表时间：
1991
影响因子：
1
通讯作者：
D. Hunt
中科院分区：
文献类型：
--
作者：
R. Wyatt;D. Hunt
从三种假定的杂交乳草和四种假定的马利筋属亲本物种的叶提取物中分离出黄酮。共鉴定出16种黄酮类化合物，均为黄酮醇类化合物槲皮素和山萘酚的糖苷。杂种A. exaltata x A. quadrifolia含有A. quadrifolia和A. exaltata。此外，还检测到两种新的黄酮类化合物。自然发生的A。exaltata x A. syriaca产生了四种诊断A. exaltata和A. exaltata，产生类似于通过实验杂交产生的已知杂交种的特征。四种新的化合物发生在现场收集的杂交种，但只存在于痕量。对西弗吉尼亚州大量乳草种群的详细分析表明，乳草种间杂种F1代的优势种为乳草。exaltata和A. syriaca与父母回交，产生了一个复杂的杂交群体。推测的杂种A. purpurascens x A. syriaca含有A. syriaca和A.紫色观察到两个新的黄酮类化合物。花提取物的分析表明，在杂交马利筋叶片中检测到的新化合物通常是由于组织特异性调节的破坏。因此，化学数据提供了有力的支持，这些物种的马利筋之间的杂交形态证据。最近的研究表明，杂交在许多被子植物类群中很常见且广泛（Grant 1971; Stebbins 1950）。一个值得注意的例外是马利筋属，它在北美包括108个物种（Woodson 1954）。Stevens（1945 a，1945 b）用人工方法培育了A.美丽托里x A.丁香属，几位植物学家从自然界中收集到了与这些杂种非常相似的植物（亚当斯等，1987;伍德森1954）。除此之外，伍德森（Woodson，1954）报告说，他在植物标本馆或野外研究过的数千个标本中，“没有发现超过12种植物可以被鉴定为种间杂种”。马利筋的授粉器官设计得如此精巧，以至于人们很自然地认为它在阻止杂交中起着重要作用（Woodson 1954）。然而，Kephart和Heiser（1980年）回顾了关于Asclepias机械生殖隔离的文献，并提出证据表明其重要性被夸大了。他们发现同域物种之间的种间授粉水平很高，这在自然界中从未观察到产生杂交种。因此，他们的结论推翻了摩尔（1946）、伍德森（1954）和怀亚特（1976）的观点，后者认为授粉后的生理障碍在乳草属植物的生殖隔离中起着至关重要的作用。然而，最近的形态学研究A.山核桃属和A.在弗吉尼亚州、西弗吉尼亚州和密歇根州的一些中间种群已经证明，乳草属物种之间确实发生了杂交（Kephart等，1988）。自从阿尔斯顿和特弗特（1963）首次应用黄酮类化合物证据来证明杂交以来，它已得到广泛的接受。其原理很简单：杂种应该产生两个亲本物种中存在的化合物的总和。在许多研究中，已经观察到这种化学互补（例如，Smith和Levin（1963）。然而，在其他情况下，涉及“新”化合物的产生的更复杂的模式（即，两个亲本物种都不能以可检测的水平积累化合物）的情况（阿尔斯顿等人，1965; King 1977; Levy和Levin 1971，1974，1975;以及其中的参考文献）。在大多数情况下，这些新化合物已被证明是由于删除或添加步骤沿着现有的生物合成途径或从组织特异性类黄酮生产的失调。本文的目的是用化学证据来检验这一假设，即来自弗吉尼亚州和西弗吉尼亚州的马利筋植物在形态上介于A。前，
Flavonoids were isolated from leaf extracts of three putative hybrid milkweeds and the four presumed parental species of Asclepias. A total of 16 flavonoids, all of which are glycosides of the flavonols quercetin and kaempferol, was identified. The hybrid A. exaltata x A. quadrifolia contained both of the marker compounds characteristic of A. quadrifolia and three of the four compounds usually produced by A. exaltata. In addition, two novel flavonoids were detected. Naturally occurring A. exaltata x A. syriaca produced three of four compounds diagnostic for A. exaltata and all but one of the common constituents of A. exaltata, yielding a profile similar to that of known hybrids produced by experimental crosses. Four novel compounds occurred in field-collected hybrids but were present only in trace amounts. Detailed analyses of a larger population of milkweeds in West Virginia suggested that F1 interspecific hybrids of A. exaltata and A. syriaca had backcrossed to the parents, yielding a complex hybrid swarm. The putative hybrid A. purpurascens x A. syriaca contained two of the four compounds characteristic of A. syriaca and four of the six variably present in A. purpurascens. Two novel flavonoids were observed. Analyses of flower extracts indicated that the novel compounds detected in leaves of hybrid milkweeds usually result from a breakdown in tissue-specific regulation. Chemical data therefore lend strong support to morphological evidence of hybridization between these species of Asclepias. Recent studies suggest that hybridization is common and widespread in many groups of angiosperms (Grant 1971; Stebbins 1950). A notable exception is the genus Asclepias, which includes 108 species in North America (Woodson 1954). Stevens (1945a, 1945b) produced artificial hybrids of A. speciosa Torrey x A. syriaca L., and several botanists have collected from nature plants that closely resemble these hybrids (Adams et al. 1987; Woodson 1954). Aside from these, Woodson (1954) reported that he had not "encountered many more than a dozen plants that [he] would construe as interspecific hybrids amongst the thousands of specimens" he had examined either in the herbarium or in the field. The pollinating apparatus of milkweeds is so elegantly contrived that it has been only natural to assume that it plays a major role in preventing hybridization (Woodson 1954). Kephart and Heiser (1980), however, reviewed the literature on mechanical reproductive isolation in Asclepias and presented evidence that its importance has been exaggerated. They found high levels of interspecific pollination between sympatric species, which were never observed to produce hybrids in nature. Their conclusions therefore paralleled those of Moore (1946), Woodson (1954), and Wyatt (1976), who argued that postpollination physiological barriers are of primary importance in reproductive isolation of milkweeds. Nevertheless, recent morphological studies of A. exaltata L. and A. syriaca and certain intermediate populations in Virginia, West Virginia, and Michigan have demonstrated that hybridization does occur between species of milkweeds (Kephart et al. 1988). The use of flavonoid evidence to document hybridization has gained wide acceptance since its first application by Alston and Turfter (1963). The rationale is simple: hybrids should produce the summation of the compounds present in the two parental species. In many studies, such chemical complementation has been observed (e.g., Smith and Levin 1963). In other cases, however, a more complex pattern involving the production of "novel" compounds (i.e., compounds not accumulated at detectable levels by either parental species) by hybrids has been reported (Alston et al. 1965; King 1977; Levy and Levin 1971, 1974, 1975; and references therein). In most cases these novel compounds have been shown to result either from deletion or addition of steps along an existing biosynthetic pathway or from deregulation of tissue-specific flavonoid production. The purpose of this paper is to use chemical evidence to test the hypothesis that milkweed plants from Virginia and West Virginia that are morphologically intermediate between A. ex-