C-20 to the alcohol and aldehyde, and then removal of this C atom with formation of the 4, 10-lactone. Each of the C20-GA intermediates in the reaction sequence is converted by GA20ox, although the alcohol intermediate must be present as the free alcohol. These alcohol intermediates form į-lactones with the 19-carboxyl group when extracted from plant tissues and are then no longer oxidized by GA20ox. It is unclear whether the į-lactones form naturally in planta, but it is of interest that vegetative tissues, but apparently not seeds, contain an enzyme capable of converted the įlactones to the aldehydes (71). This enzyme may serve to ensure formation of C19-GAs when GA20ox activity is low, as in vegetative tissues, when lactone formation may compete with further oxidation of the alcohol intermediate. In most systems C20-GAs containing a 20-carboxylic acid group are formed by GA20ox as minor biologically inactive by-products, which are not converted to C19-GAs.
C-20 to the alcohol and aldehyde, and then removal of this C atom with formation of the 4, 10-lactone. Each of the C20-GA intermediates in the reaction sequence is converted by GA20ox, although the alcohol intermediate must be present as the free alcohol. These alcohol intermediates form į-lactones with the 19-carboxyl group when extracted from plant tissues and are then no longer oxidized by GA20ox. It is unclear whether the į-lactones form naturally in planta, but it is of interest that vegetative tissues, but apparently not seeds, contain an enzyme capable of converted the įlactones to the aldehydes (71). This enzyme may serve to ensure formation of C19-GAs when GA20ox activity is low, as in vegetative tissues, when lactone formation may compete with further oxidation of the alcohol intermediate. In most systems C20-GAs containing a 20-carboxylic acid group are formed by GA20ox as minor biologically inactive by-products, which are not converted to C19-GAs.
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