Pollen-ovule Ratios in Milkweeds (Asclepiadaceae): an Exception that Probes the Rule
Pollen-ovule Ratios in Milkweeds (Asclepiadaceae): an Exception that Probes the Rule
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马利筋（萝藦科）的花粉胚珠比率：探索规则的例外
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
S. Lipow
中科院分区：
文献类型：
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作者：
R. Wyatt;S. B. Broyles;S. Lipow
与大多数高度异交的开花植物不同，乳草（Asclepiadaceae）具有非常低的花粉-胚珠比率。对38种天门冬科植物的花粉囊内的花粉粒数和子房内的胚珠数进行了统计。每个花粉粒数在14 ~ 445粒之间，每个子房的胚珠数在4 ~ 229粒之间。然而，花粉-胚珠比被限制在一个狭窄的范围内，一般为1 ~ 2。类似的花粉-胚珠比例限制也发生在豆科植物（金合欢、金合欢、印加）中，它们的花粉也以簇状分散（多聚体）。我们的数据与花粉凝集的进化与胚珠数一致，以尽量减少接收混合花粉负荷的可能性，而与花粉-胚珠比例反映育种系统或授粉效率的观点不一致。花粉粒和胚珠数的变化趋势似乎不反映分类上的亲缘关系，而是反映生态地理压力。通讯编辑：Paul Wilson
Abstract Unlike most highly outcrossing flowering plants, milkweeds (Asclepiadaceae) have exceptionally low pollen-ovule ratios. We counted the number of pollen grains contained within a pollinium sac and the number of ovules contained within an ovary for 38 species of Asclepiadaceae. Across four tribes of the Asclepiadoideae, the number of pollen grains per pollinium varied from 14 to 445, and the number of ovules per ovary varied from 4 to 229. Nevertheless, the pollen-ovule ratio was constrained within a narrow range, generally 1 to 2. Similar constraints on pollen-ovule ratios occur within mimosoid legumes (Acacia, Calliandra, Inga) whose pollen also is dispersed in clusters (polyads). Our data are consistent with the view that agglutination of pollen evolves in concert with ovule number to minimize the likelihood of receiving mixed pollen loads and are not consistent with the view that pollen-ovule ratios reflect breeding system or pollination efficiency. Trends in pollen grain and ovule number do not appear to reflect taxonomic affinities, but rather ecogeographical pressures. Communicating Editor: Paul Wilson