| Popis: |
Differentiation of the tube cells and cross cells, which in the early stages of development constitute the photosynthetic tissue of the pericarp of grasses, was investigated in wheat (Triticum aestivum L. 'Heron') using light and electron microscopy. In the developing tube cells, scattered amyloplasts contain starch deposits as early as 3 days after anthesis. Abundant starch reserves occur in the cross cells and in some of the tube cells within well-defined chloroplasts by 10 days after anthesis. By this time the outer integument has degenerated completely and the tube cells are adherent to the outer cuticle of the developing seed coat. The cytoplasm of the tube cells begins to degenerate between 14 and 17 days after anthesis. Starch reserves persist in the chloroplasts of the cross cells up to 21 days after anthesis, which marks the beginning of the change in color of the developing grains from green to yellow. Plasmodesmata, which could provide a route for translocation of photosynthate to the chalazal ... |
