小麦胚胎分化时营养吸收一种可能方式的细胞学论据

Cytological Evidences of a Possible Mode of Nurture Absorption of the Differentiating Embryo in Triticum aestivum 

以光学与电子显微镜术结合荧光标记物示踪，对小麦（ＴｒｉｔｉｃｕｍａｅｓｔｉｖｕｍＬ．）胚胎分化时胚根鞘的形态结构特征的变化与营养吸收相联系进行了实验观察。发现在分化前期胚根鞘顶端的球状突起处和颈区朝向颖果背面一侧的特定位点上出现了结构的变更；外沿局部细胞的衰退瓦解导致这些区段内侧存活细胞分界壁上出现大量残存的胞间连丝。不透膜的荧光物质、分子量达４３ｋＤ的ＦＩＴＣｄｅｘｔｒａｎ可进入球状突起和颈区多处细胞，表明残存胞间连丝仍具有共质传输功能，是分化幼胚摄取外围介质中营养物质的一种方式。分化进程中颈区的短时期局部缺损与随后的修复以及衰退区周围多层细胞胞间通透性的显著增大，既有利于外源物质的适时与大量掺入和在细胞间的快速运转，并仍保持了胚根鞘的结构完整，与分化前期胚胎对养分的大量需求正相适应，显示出胚根鞘的颈区比之球状突起处在营养吸收上占有更重要的地位。

Coleorhiza covered the radicle of differentiating wheat embryo and morphologically appeared as tapered tissue with an attached globular protrusion. In the early phase of differentiation a series of structural changes occurred at some local areas of the coleorhiza. By light and electron microscopic inspections combined with fluorescence labelling it was uncovered that cells of the peripheral layers of the globular protrusion and the neck region underneath gradually exhibited degeneration and disintegration while a lot of broken plasmodesmata still remained at the boundary wall of the inner surviving cells. Impermeable fluorescence probe 4.3 kD FITC dextran could enter these living cells and continuously diffuse to their neighborhood. All these showed that a direct communication was established between the symplasm of coleorhiza and the external medium and the remaining plasmodesmata, though broken in one end, might function as symplasmic pathway for external material incorporation. Analyzing the above described results a possible mode of nurture absorption of differentiating embryo then could be recognized; particularly, comparing with the globular protrusion the limited area of the neck region towards dorsal side might play a more important role in nurture absorption of the young embryo. Temporal and partial disintegration of the neck region and consequential regeneration in situ and increase of plasmodesmatal conductivity in the surrounding surviving cell group were most favourable to the incorporation and intercellular translocation of the external material for the coleorhiza. A large quantity of nutrients intruding into the coleorhiza at proper instant through the transiently opened route would effectively coordinate with the need of embryo differentiation without leaving apparent destruction to the coleorhiza.