Gibberellic acid (GA₃)‐induced enhancement of α‐amylase activity in the aleurone of Shrunken‐2 maize kernels

Abstract

The aleurone of RB‐3 shrunken‐2 (sh2) maize kernels is deficient in α‐amylase activity during germination, but exogenous applications of gibberellic acid (GA3) (0.001–10 μm) induced low levels of activity. The highest activity was measured in the aleurone of kernels treated with 10 μm GA3 (14,600 ± 945 units), but was lower than untreated Starchy (Su) aleurone tissues (35,280 ± 5,010 units). On isoelectric focusing gels, no α‐amylase isozymes were detected in the untreated sh2 aleurone using starch zymograms or immunoblots, but the 1.0 and 10 μmmm GA3 treatments induced nearly all the isozymes (eight to ten) present in the Su aleurone. There was a very low level of α‐amylase mRNA in the untreated sh2 aleurone, an intermediate level in the 1.0 μm GA3‐treated sh2 aleurone, and the highest level in the untreated Su aleurone. On the confocal microscope, the 1.0 μm GA3‐treated aleurone cells had enhanced levels of cytoplasmic membranes and RNA compared to untreated sh2 aleurone cells. The 1.0 μm GA3 treatment also induced shoot elongation in the sh2 seedlings. The data demonstrate that the sh2 aleurone is deficient in its function to produce α‐amylases, and exogenous GA3 can partially restore cell function in the sh2 kernels.