THE EFFECT OF THE sh 2 FACTOR ON CARBOHYDRATE RESERVES IN THE MATURE ENDOSPERM OF MAIZE

Abstract

H E R E are many mutants in maize which produce striking differences T from normal in the texture, form and amount of the endosperm. Since an overwhelming proportion of the normal endosperm of maize is composed of reserve carbohydrate, principally starch, it might be anticipated that studies on the action of such mutant forms would have significance for the problem of the biosynthesis of carbohydrates. This is a report of some rather striking effects of one such mutant gene, shrunken-2 (sh;:), whose occurrence and linkage relations were reported by MAINS (1948). Mature endosperms having the constitution sla sla sh are highly collapsed, opaque and brittle and have a weight of 75 percent that of normal endosperms. Judging by appearance, the normal allele is completely dominant to shq, Sh Sh sh and Sh sh sh endosperms being indistinguishable from normal (S h Sh S h). Because of its close linkage with the al factor, sh2 has been employed as a technical aid in studies of certain of the alleles at the former locus. In the course of these investigations it was noted that the shrunken kernels are unusually sweet and have a pleasant, malty flavor. Biochemical studies have confirmed the former observation and indicate that the high concentration of sugars in these endosperms is due to sucrose primarily and is attained at the expense of polysaccharides. MATERIALS AND METHODS The gene sit1 is the basis for the " sugary " endosperm which is characteristic of our present commercial varieties and hybrids of sweet corn and of many strains of maize indigenous to Mexico, South America and our Southwest (STURTEVANT 1899). Previous studies (PEARL and BARTLETT 191 1 ; LINDSTROM and GERHARDT 1926, 1927; ANDREW, BRINK and NEAL 1944) have established that mature sugary endosperms (su su su) have from two to three times as much total sugar as those of starchy (Su Su S u). In view of the higher sugar level associated with su and of an anticipated effect of shrunken-2 (hereafter designated shrunken or sh) on the distribution of carbohydrate reserves, the present study was carried out with progenies permitting a valid comparison of the effects of both factors. Accordingly, two different plants of commercial Golden Cross Bantam (su su Sh S h) were crossed with a single plant of the constitution Su Su sh sh. The F1 plants from these two ears were grown in two families in the summer of 1952 and self-pollinated. Since both normal alleles carried by the F1 plants are dominant, four phenotypic classes GENETICS 38: 485 September 1953.