Developmental changes in the branched parenchyma cells of bean-seed coat

Summary

Structural specializations occuring in the branched parenchyma cells of the bean-seed coat start at the globular stage of embryo development with the formation of rough endoplasmic reticulum (RER). In the heart stage, the cytoplasm of the branched parenchyma cells is gradually filled with an extensive system of RER cisternae. Other cytoplasmic organelles also increase in abundance, particularly the dictyosomes and mitochondria. In the cotyledon stage, the ER cisternae become dilated and form a labyrinthine system of intercommunicating spaces separated by channels of cytoplasm. There is little further change in the overall ultrastructural pattern of the cell till the maturation stage. At this stage, the ER cisternae become gradually reduced in size and fragmented into short segments. Other cytoplasmic organelles are also greatly reduced in number. As the seed starts to dry out, these parenchyma cells are crushed and dehydrated.