Maize alpha-amylase: purification and properties and induction by gibberellic acid

Abstract

Alpha-amylase synthesis can be induced in wheat and barley half-seeds by addition of gibberellic acid (GA) to the incubation medium. In maize, induction in de-embryonated kernels by exogenous GA has been reported in some studies but not others.

Alpha-amylase induction was investigated in maize by measuring activity in extracts from whole and de-embryonated kernels incubated with and without GA during germination. Alpha-amylase activity was first detected on the 3rd day of germination in whole kernels and GA-treated endosperms and on the 4th day in the controls. Thereafter both whole kernels and GA-treated endosperms followed approximately the same time course in α-amylase activity with the control lagging a day behind. Studies indicated that maximum α-amylase activity occurred on the 7th day in whole kernels and GA-treated endosperms and the 8th in control endosperms.

Maize α-amylase was purified using differential solubility, column chromatography, glycogen precipitation and polyacrylamide gel electrophoresis, of these, the best purification method was glycogen precipitation.

Maize α-amylase exhibited isozymes. The isozyme patterns were qualitatively similar in all samples and throughout incubation. Wheat and barley α-amylase isozymes have been divided into two groups on the basis of a number of characteristics. Genetics analysis revealed these isozymes to be the result of two multigene families. To shed light on the genetic basis of the maize α-amylase isozymes, physicochemical characterization was initiated. Studies of pH and temperature profiles and optima showed no differences between maize isozymes. The pH optima was pH 5 and the temperature optima was about 37°C.