When seeds germinate, how do plant fats turn into sugar?

After fatty acids in plant cells are oxidized and decomposed into acetyl coenzyme A, succinic acid, glyoxylic acid and malic acid are generated in glyoxylate. This succinic acid can be used in the synthesis of sugar.

Glyoxylic acid cycle only exists in some plant cells, such as cotyledons and endosperm cells of oil plant seeds, and often coexists with mitochondria. When this kind of seeds germinate, the number of glyoxylic acid circulators increases obviously, because it is not only a place for β -oxidation of fat, but also a place for glyoxylic acid circulating enzymes.

Extended data

During the germination of oilseed, many glyoxylic acids appear in cells. The stored fat is hydrolyzed into glycerol and fatty acids, and then the fatty acids are oxidized and decomposed into acetyl coenzyme A in glyoxylic acid, which is converted into sugar through glyoxylic acid cycle. The glyoxylic acid cycle activity did not disappear until the fat stored in the seeds was exhausted.

Glyoxylic acid cycle does not occur when starch seeds germinate. It can be seen that glyoxylic acid cycle is a unique respiratory metabolic pathway of oil seeds rich in fat.

Later, in the process of studying the transformation from fat to sugar during the germination of castor seeds, the above glyoxylic acid circulation pathway was reformed. Firstly, malic acid formed by the combination of glyoxylic acid and acetyl-CoA does not dehydrogenate, but directly enters the cytoplasm and is converted into sucrose by reverse glycolytic pathway. Secondly, there is a "malic acid shuttle" between glyoxylic acid and mitochondria.

Through "malic acid shuttle" and transamination reaction, the regeneration of NAD+ in glyoxylic acid and the continuous supplement of OAA are solved, which is very important to ensure the normal operation of GAC.

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