GIBBERELLIC-ACID (GA(3))-INDUCED ENHANCEMENT OF ALPHA-AMYLASE ACTIVITY IN THE ALEURONE OF SHRUNKEN-2 MAIZE KERNELS

The aleurone of RB-3 shrunken-2 (sh2) maize kernels is deficient in al pha-amylase activity during germination, but exogenous applications of gibberellic acid (GA(3)) (0.001-10 mu M) induced low levels of activi ty. The highest activity was measured in the aleurone of kernels treat ed with 10 mu M GA(3) (14,600 +/- 945 units), but was lower than untre ated Starchy (Su) aleurone tissues (35,280 +/- 5,010 units). On isoele ctric focusing gels, no alpha-amylase isozymes were detected in the un treated sh2 aleurone using starch zymograms or immunoblots, but the 1. 0 and 10 mu M GA(3) treatments induced nearly all the isozymes (eight to ten) present in the Su aleurone. There was a very low level of alph a-amylase mRNA in the untreated sh2 aleurone, an intermediate level in the 1.0 mu M GA(3)-treated sh2 aleurone, and the highest level in the untreated Su aleurone. On the confocal microscope, the 1.0 mu M GA(3) -treated aleurone cells had enhanced levels of cytoplasmic membranes a nd RNA compared to untreated sh2 aleurone cells. The 1.0 mu M GA(3) tr eatment also induced shoot elongation in the sh2 seedlings. The datain its function to produce alpha-amylases, and exogenous GA(3) can parti ally restore cell function in the sh2 kernels.