Comparative susceptibility to amylases of starch granules of several single endosperm mutants representative of floury-opaque, starch-deficient, and modified starch types and their double-mutant combinations with opaque-2 in four inbred lines of maize.

Starch granules were prepared from kernels of eight single endosperm mutants, brittle-1, (bt1), brittle-2 (bt2), floury-1, floury-2, soft starch, opaque-1 (o1), shrunken-2 (sh2), and sugary-2 (su2), and their double-mutant combinations with opaque-2 (o2) of four inbred lines of maize (Zea mays L.), B37, C103, Oh43 and W64A. We compared the susceptibility of various starch granules to Rhizopus glucoamylase and pancreatin. Starch granules of the su2 and su2o2 mutants were digested by amylases much faster than those of the normal counterparts. Starch granules of the bt1, bt2, o1 and sh2 mutants tended to be digested by amylases faster than those of normal maize. Starch granules of double-mutant combinations with the o2 gene were, in general, digested to an extent very comparable to their respective non-opaque single mutant counterparts in each of their four inbred backgrounds. We followed the relative digestion of starch granules by using scanning electron microscopy. Starch granules of endosperm mutants susceptible to amylases showed numerous pin holes on the surface layer and the pores penetrated into the inner layers of the granules during the attack by amylases. In some of the granules the inner portion, which appeared terraced or step-shaped, could be seen. This may be indicative of layered internal structures of the granules.