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

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 estabhshed 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 bo recognized; particularly, comparing with the globular pretmsion 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.