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Synthesis
of L-ascorbic acid in Vigna mungo sprouts: sequential development of the
enzymes involved in the synthesis and metabolism American Society of Plant Biologists Abstract
Number:1640 Presented
by: Oba, Kazuko, Department of Food Science and Nutrition, Nagoya Women's
University
The levels of
L-ascorbic acid (AsA) are relatively high in bean sprouts, while a very low in
dry seeds. To elucidate the mechanism of increase in AsA in bean sprouts, we
studied changes in the levels of AsA and dehydro-AsA and in the activities of
enzymes involved in AsA synthesis and degradation in cotyledons and axes of Vigna
mungo during germination in the dark. Levels of AsA in both cotyledons and
axes of the germinating sprout were increased after 1-day lag period, and
reached maximum in the fresh weight base in 2 days after the imbibition in water
at 27 C. The activity of L-galactono-gamma-lactone dehydrogenase (EC 1.3.2.3,
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 in
axes in the bases of fresh weight and mg protein. The increase in the activity
of cotyledons after 1-day imbibition was not inhibited by cycloheximide (5
mg/ml). Activities of ascorbate oxidase (EC 1.10.3.3, AAO) and ascorbate
peroxidase (EC 1.11.1.11, APO) were increased in both cotyledons and axes after
2-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 APO
were dominant in axes and the developments after germination were completely
inhibited by cycloheximide treatment. |