The water content of germinating seeds fluctuates in response to water potential changes in the surrounding environment. We tested the hypothesis that the endosperm functions as a water reservoir when imbibed seeds experience drying, and we characterized water uptake and movement within barley (Hordeum vulgare cv. Triumph) caryopses (hereafter referred to as seeds). Water movement into and through germinating barley seeds during imbibition and drying was determined gravimetrically and with the fluorescent dye trisodium 8‐hydroxy‐1,3,6‐pyrenetrisulfonate (PTS). During imbibition, embryo tissues hydrated more rapidly and reached a higher water content (g H20/g dry weight) than did the endosperm, although the endosperm eventually contained nine times as much total water. When barley seeds that had imbibed for 12 h were exposed to moderate (−4 MPa) drying, PTS solution moved from the endosperm into the shoot meristem, radicle, and scutellum, but not vice versa. Radicle emergence and elongation proceeded for up to 8 h. With harsh (−150 MPa) drying, PTS concentrated almost exclusively in the radicle. These data illustrate that the endosperm is at least a temporary water storage compartment external to the embryo itself. We speculate that water supplied by the endosperm may be important in reducing the harmful effects of drying during the critical transition period when a germinating seed changes from a desiccation‐tolerant to a desiccation‐intolerant organism.

中文翻译：

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当发芽的种子干燥时，大麦胚乳是胚胎的水库吗？

发芽种子的含水量随着周围环境的水势变化而波动。我们测试了当吸收的种子经历干燥时胚乳充当水库的假设，并且我们描述了大麦（Hordeum vulgare cv. Triumph）颖果（以下称为种子）内的吸水和运动特征。在吸收和干燥过程中，水分进入和通过发芽的大麦种子是通过重量分析法和荧光染料 8-羟基-1,3,6-芘三磺酸三钠 (PTS) 测定的。在吸胀过程中，胚胎组织的水合速度更快，并达到比胚乳更高的含水量（g H2O/g 干重），尽管胚乳最终含有的总水分是其 9 倍。当吸收 12 小时的大麦种子暴露于中等 (-4 MPa) 干燥时，PTS 溶液从胚乳移动到芽分生组织、胚根和盾片中，但反之则不然。胚根出现和伸长持续长达8小时。在苛刻的 (-150 MPa) 干燥条件下，PTS 几乎完全集中在胚根中。这些数据说明胚乳至少是胚胎本身外部的临时储水隔间。我们推测，当发芽的种子从耐干燥有机体转变为不耐干燥有机体时，胚乳提供的水可能对减少关键过渡期干燥的有害影响很重要。胚根出现和伸长持续长达8小时。在苛刻的 (-150 MPa) 干燥条件下，PTS 几乎完全集中在胚根中。这些数据说明胚乳至少是胚胎本身外部的临时储水隔间。我们推测，当发芽的种子从耐干燥生物转变为不耐干燥生物时，胚乳提供的水可能对减少关键过渡时期干燥的有害影响很重要。胚根出现和伸长持续长达8小时。在苛刻的 (-150 MPa) 干燥条件下，PTS 几乎完全集中在胚根中。这些数据说明胚乳至少是胚胎本身外部的临时储水隔间。我们推测，当发芽的种子从耐干燥生物转变为不耐干燥生物时，胚乳提供的水可能对减少关键过渡时期干燥的有害影响很重要。