SH2 Mutant Research Articles

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.

Interaction of Shrunken‐2 and Sugary‐1 in Dosage Series in Corn Endosperm1

The interaction of gone dosage on Zea mays L. endosperm carbohydrate composition was studied by quantifying carbohydrates from the 16 genotypes of 21‐day‐old endosperm resulting from all possible sib‐pollinations and reciprocal crosses between lines homozygous for Su1 Sh2 (normal), su1 Sh2 (sugary‐1), Su1 sh2 (shrunken‐2), and su1 sh2 (sugary‐1; shrunken‐2). No dosage effects were produced by either the allele su1 or the allele sh2 for fructose and glucose sugars and starch content of the endosperm. There was a dosage effect of su1 on sucrose content in the homozygous recessive sh2 genotypes. Two and three doses of su1 allele produced a 10 and 26% increase in sucrose content, respectively, over the zero or one dose level of su1. Two doses of su1 produced a very slight increase in water‐soluble polysaccharide (WSP) and three doses produced large amounts of WSP typical of su1. Two doses of sh2 reduced the WSP content of the homozygous recessive su1 genotype and the presence of three doses of sh2 considerably decreased the amount of WSP accumulated at 21 days after pollination. The interaction effects suggested that WSP accumulation in homozygous su1 may be affected by the dosage level of the sh2 mutant. Starch synthesis was markedly decreased in homozygous recessive su1, sh2 and su1 sh2 genotypes.

Effect of Endosperm Mutants on Pericarp Thickness in Corn1

Pericarp thickness was measured for mutant and normal kernels obtained from ears segregating for various endosperm mutants in the corn (Zea mays L.) inbred lines Oh43 and B37. The pericarp, being maternal tissue, was not greatly influenced by the genotype of the endosperm when averaged over all mutants. In the B37 series, only the pericarp thickness for the sh2 mutant significantly exceeded its normal sibbed kernels. while in the Oh43 series, ae and su2 mutant kernels had significantly thicker pericarp tissue and su1 mutant kernels had thinner pericarp. While significant these differences were small in magnitude. There is a lack of evidence for a metaxenia effect of endosperm phenotype on pericarp thickness when averaged over all nine mutants.