Linder C Randal
Am Nat. 2000 Oct;156(4):442-458. doi: 10.1086/303399.
Structural, energetic, biochemical, and ecological information suggests that germination temperature is an important selective agent causing seed oils of higher-latitude plants to have proportionately more unsaturated fatty acids than lower-latitude plants. Germination temperature is predicted to select relative proportions of saturated and unsaturated fatty acids in seed oils that optimize the total energy stores in a seed and the rate of energy production during germination. Saturated fatty acids store more energy per carbon than unsaturated fatty acids; however, unsaturated fatty acids have much lower melting points than saturated fatty acids. Thus, seeds with lower proportions of saturated fatty acids in their oils should be able to germinate earlier and grow more rapidly at low temperatures even though they store less total energy than seeds with a higher proportion of saturated fatty acids. Seeds that germinate earlier and grow more rapidly should have a competitive advantage. At higher germination temperatures, seeds with higher proportions of saturated fatty acids will be selectively favored because their oils will provide more energy, without a penalty in the rate of energy acquisition. Macroevolutionary biogeographical evidence from a broad spectrum of seed plants and the genus Helianthus support the theory, as do microevolutionary biogeography and seed germination performance within species of Helianthus.
结构、能量、生化和生态信息表明，萌发温度是一种重要的选择因子，导致高纬度地区植物种子油中的不饱和脂肪酸比例高于低纬度地区植物。预计萌发温度会选择种子油中饱和脂肪酸和不饱和脂肪酸的相对比例，以优化种子中的总能量储存以及萌发过程中的能量产生速率。每单位碳原子，饱和脂肪酸比不饱和脂肪酸储存更多能量；然而，不饱和脂肪酸的熔点远低于饱和脂肪酸。因此，油中饱和脂肪酸比例较低的种子应该能够在低温下更早萌发并生长得更快，尽管它们储存的总能量比饱和脂肪酸比例较高的种子少。更早萌发且生长更快的种子应该具有竞争优势。在较高的萌发温度下，饱和脂肪酸比例较高的种子将被选择性地青睐，因为它们的油将提供更多能量，且不会在能量获取速率上受到影响。来自广泛种子植物和向日葵属的宏观进化生物地理学证据支持了这一理论，向日葵属物种内的微观进化生物地理学和种子萌发表现也支持这一理论。
