Connor Kristina F, Sowa Sharon
USDA Forest Service, Center for Bottomland Hardwoods Research, Box 9681, Mississippi State, MS 39762, USA.
Tree Physiol. 2003 Nov;23(16):1147-52. doi: 10.1093/treephys/23.16.1147.
Seeds that lose viability when dried to a water content of less than 12% are said to be recalcitrant. We subjected acorns of Quercus alba L., a species with recalcitrant seeds, to desiccation to determine the effects of drying on lipids, proteins and carbohydrates of the embryonic axis and cotyledon tissues. Samples of fresh seed and seed dried for selected intervals were analyzed for water content and germination, and for lipids, proteins and carbohydrates by Fourier transform-infrared (FT-IR) spectroscopy. Carbohydrates were further analyzed by gas chromatography (GC). The FT-IR analysis revealed that membrane lipid structure initially exhibited reversible shifts between gel and liquid crystalline phases in response to drying and rehydration; however, reversibility declined as viability was lost. Changes in carbohydrate concentration were observed based on peak height comparisons; sucrose concentration in the embryonic axis increased dramatically after 5 days of drying. The most sensitive indicator of desiccation damage was the irreversible change in protein secondary structure in embryonic axes and cotyledon tissue. These changes were illustrated by shifts in amide absorbance near 1650 cm(-1). Gas chromatography indicated an abundance of sucrose in both the embryonic axes and the cotyledon tissue. Although sucrose concentrations in these tissues were initially similar, sucrose concentration in the embryonic axes became significantly greater than in the cotyledons as the acorns dried. We hypothesize that, in drying acorns, increased concentration of sucrose does not prevent loss of viability, but acts as a glycoprotectant against cell collapse and cell wall membrane damage as water stress increases.
当种子干燥至含水量低于12%时失去活力，这类种子被称为顽拗性种子。我们对具有顽拗性种子的白栎（Quercus alba L.）橡子进行干燥处理，以确定干燥对胚轴和子叶组织中脂质、蛋白质和碳水化合物的影响。分析新鲜种子样本以及经过选定时间段干燥处理的种子样本的含水量、发芽率，并通过傅里叶变换红外（FT-IR）光谱分析脂质、蛋白质和碳水化合物。碳水化合物进一步通过气相色谱（GC）进行分析。FT-IR分析表明，膜脂结构最初在干燥和复水过程中会在凝胶相和液晶相之间呈现可逆转变；然而，随着活力丧失，可逆性下降。基于峰高比较观察到碳水化合物浓度的变化；干燥5天后，胚轴中的蔗糖浓度急剧增加。干燥损伤最敏感的指标是胚轴和子叶组织中蛋白质二级结构的不可逆变化。这些变化通过1650 cm(-1)附近酰胺吸光度的变化得以体现。气相色谱表明胚轴和子叶组织中都有大量蔗糖。虽然这些组织中的蔗糖浓度最初相似，但随着橡子干燥，胚轴中的蔗糖浓度显著高于子叶中的蔗糖浓度。我们推测，在干燥的橡子中，蔗糖浓度增加并不能防止活力丧失，但随着水分胁迫增加，它作为一种糖保护剂可防止细胞塌陷和细胞壁膜损伤。
