Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds

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Abstract
The ultrastructural changes occurring in the scutellar epithelium cells of rice seeds were studied during germination and early seedling growth. During this time, several prominent structural changes occur, including formation, development and proliferation of organelles such as mitochondria, rough endoplasmic reticulum, free ribosomes and Golgi apparatus; folded structural modification of plasmamembranes in later stages; and conspicuous decrease in lipid-storing spherosomes. Glyoxysome-like electron dense particles are detectable but their formation is much less prominent. All these structural changes may be related to the enhancement of the metabolic activities of the epithelial cells including the synthesis of hydrolytic enzymes such as .alpha.-amylase and their secretion into the endosperm tissues. Some enzyme activities characteristic of mitochondria and glyoxysomes were determined using the crude scutellar extracts and the results dealing with the low activities of the glyoxylate cycle enzymes and palmitoyl-coA oxidase appear to indicate that fatty acid breakdown is possibly via mitochondrial .beta.-oxidation.