J Integr Plant Biol. ›› 1985, Vol. 27 ›› Issue (4): -.

• Research Articles •    

Ultrastructural Studies on the Degeneration Processes in Wheat Nucellar Cells

You Rui-lin   

Abstract: During its development and enlargement, the embryo sac encroachesupon adjoining nucellar cells continuously, leading to their degeneration completely. Thefirst signs of degeneration appear in the vacuolated nucellar cells at a distance to theembryo sac. In the process, two types of degeneration are found in wheat nucellarcells. In type I the degeneration is carried out through the in situ autolysis of theircytoplasm. The ribosome density decreases drastically in the cytoplasm of the nucellarcells. Organelles therein become suspended in a more diluted cytoplasmic matrix. Debris of dissolved cytoplasmic components distribute throughout the cytoplasm andvacuoles. Chromatin masses in the nucleus decrease obviously or chromatin becomecondensed in the mean time. Degenerate cells of this type become empty and dead atlast, lying on the border of the embryo sac. Type Ⅱ of degeneration is quite contrary to the first, the process is carried out through the proliferation and dilation ofrough endoplasmic reticulum cisternae, and their engulfment and sequestering of thecytoplasmic components. Degeneration type Ⅱ is associated with the increasing affinityof dyes, such as lead, in the protoplast. Finally, plasma membrane and tonoplast breakdown, protoplast shrinks and converts to a dark disorganized mass. During the process of the degeneration type Ⅱ, a series of complicated changes occur in the nucleusand cytoplasm.

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