Shao Suqin, Meyer Chris J, Ma Fengshan, Peterson Carol A, Bernards Mark A
Environmental Stress Biology Group, Department of Biology, University of Western Ontario, London, ON, Canada N6A 5B7.
J Exp Bot. 2007;58(5):1071-82. doi: 10.1093/jxb/erl268. Epub 2007 Jan 11.
Seeds of different cultivars of Glycine max (L.) Merr. (soybean) have strikingly different rates of water imbibition. Seeds that readily imbibe water are termed 'soft', while those that remain non-permeable, even after several days in water, are referred to as 'hard', 'stone', or 'impermeable' seeds. What prevents soybean hard seeds from taking up water? Previous work established that the initial imbibition of soft soybean seeds correlates with the presence of small cracks in the outermost cuticle that covers the seed coat, prompting a detailed analysis of soybean seed coat cutin. In this paper, it is shown that the outermost cuticle of the seed coat has an unusual chemical composition, lacking typical mid-chain-hydroxylated fatty acids but being relatively rich in other types of hydroxylated fatty acids. The cuticle of the impermeable cultivar studied contained a disproportionately high amount of hydroxylated fatty acids relative to that of the permeable ones. Moreover, a brief treatment with hot alkali released the omega-hydroxy fatty acid component of the outermost cuticle and created holes in it that caused the seeds to become permeable. This demonstrates that the outermost cuticle of the seed is the critical structure that prevents water uptake by hard seeds.
不同品种的大豆（Glycine max (L.) Merr.）种子具有显著不同的水分吸收速率。容易吸收水分的种子被称为“软”种子，而那些即使在水中浸泡几天后仍不渗透的种子则被称为“硬”种子、“石”种子或“不透水”种子。是什么阻止了大豆硬种子吸收水分？先前的研究表明，软大豆种子的初始吸水与覆盖种皮的最外层角质层中存在小裂缝有关，这促使对大豆种皮角质进行详细分析。本文表明，种皮的最外层角质层具有不寻常的化学成分，缺乏典型的中链羟基化脂肪酸，但相对富含其他类型的羟基化脂肪酸。所研究的不透水品种的角质层相对于透水品种含有不成比例的大量羟基化脂肪酸。此外，用热碱进行短暂处理会释放最外层角质层的ω-羟基脂肪酸成分，并在其中形成孔洞，使种子变得透水。这表明种子的最外层角质层是阻止硬种子吸收水分的关键结构。
