Synthesis of L Ascorbic Acid in Vigna Mungo Sprouts
Synthesisof L-ascorbic acid in Vigna mungo sprouts: sequential development of theenzymes involved in the synthesis and metabolism
AmericanSociety of Plant Biologists
Presentedby: Oba, Kazuko, Department of Food Science and Nutrition, Nagoya Women’sUniversity
The levels ofL-ascorbic acid (AsA) are relatively high in bean sprouts, while a very low indry seeds. To elucidate the mechanism of increase in AsA in bean sprouts, westudied changes in the levels of AsA and dehydro-AsA and in the activities ofenzymes involved in AsA synthesis and degradation in cotyledons and axes of Vignamungo during germination in the dark. Levels of AsA in both cotyledons andaxes of the germinating sprout were increased after 1-day lag period, andreached maximum in the fresh weight base in 2 days after the imbibition in waterat 27 C. The activity of L-galactono-gamma-lactone dehydrogenase (EC 22.214.171.124,GLDH) was scarcely detected in dry seeds and increased rapidly after the imbibition and then reached maximum after 2 to 3 days in cotyledons and 1 day inaxes in the bases of fresh weight and mg protein. The increase in the activityof cotyledons after 1-day imbibition was not inhibited by cycloheximide (5mg/ml). Activities of ascorbate oxidase (EC 126.96.36.199, AAO) and ascorbateperoxidase (EC 188.8.131.52, APO) were increased in both cotyledons and axes after2-days lag period and reached maximum after 3 days and 4 days, respectively.GLDH activity was higher than AAO activity in the early stage of germination(1-2 day), but lower in the later stage (3-5 days). Activities of AAO and APOwere dominant in axes and the developments after germination were completelyinhibited by cycloheximide treatment.