Terui Keisuke, Okagami Nobuo
Department of Biology, Faculty of Education, Iwate University, Morioka, 020, Japan.
Biological Institute, Faculty of Science, Tohoku University, Sendai, 980, Japan.
Am J Bot. 1993 May;80(5):493-499. doi: 10.1002/j.1537-2197.1993.tb13832.x.
To obtain information relevant to the evolution of dormancy, germination responses to temperature of intact seeds and naked zygotic embryos were compared among taxonomically closely related species of Dioscorea in the section Stenophora. We examined five species from the northern half of the East Asian distribution area and four species considered to be Tertiary relict species from the Appalachians, the Caucasus, and the Balkans. Although features of germination of the intact seeds differed from species to species, the naked embryos of all species germinated over a similar wide range of temperatures without any marked differences among species. This unitary physiological feature of the embryos suggests the possibility that the temperature responses of the embryos have not changed since the Tertiary period. In the East Asian species, as the distribution area shifts to the north the seeds gradually lose their dormant features, and consequently the germination behavior of the seeds gradually changes to resemble that of their embryos. The seed of the northernmost species has no dormant features at all, and temperature responses of the seed are the same as those of the embryo. Full germination of the intact seeds of East Asian and Tertiary relict species required prior chilling treatment. Unlike the East Asian species, however, the relict species germinated to some extent at higher temperatures over a narrow range without prior chilling. However, the resultant germlings died or elongated poorly. Thus, the germination process of relict species may have become less sensitive to high-temperature inhibition after their isolation from Asian species.
为获取与休眠进化相关的信息，我们比较了薯蓣属Stenophora组分类学上亲缘关系较近的物种中完整种子和裸露合子胚对温度的萌发反应。我们研究了东亚分布区北半部的五个物种以及四个被认为是来自阿巴拉契亚山脉、高加索地区和巴尔干半岛的第三纪残遗物种。尽管完整种子的萌发特征因物种而异，但所有物种的裸露胚在相似的较宽温度范围内萌发，物种间没有明显差异。胚的这种单一生理特征表明，自第三纪以来胚的温度反应可能没有改变。在东亚物种中，随着分布区向北移动，种子逐渐失去休眠特征，因此种子的萌发行为逐渐变得类似于其胚的萌发行为。最北部物种的种子完全没有休眠特征，种子的温度反应与胚相同。东亚和第三纪残遗物种完整种子的完全萌发需要预先进行低温处理。然而，与东亚物种不同的是，残遗物种在没有预先低温处理的情况下，在较窄的高温范围内能有一定程度的萌发。然而，由此产生的幼苗死亡或生长不良。因此，残遗物种与亚洲物种隔离后，其萌发过程可能对高温抑制变得不那么敏感。
