Changes in Seed Structure and Composition during Development and Their Effects on Leakage in Two Endosperm Mutants of Sweet Corn

Abstract

Field- and greenhouse-grown seeds of 2 sweet corn (Zea mays L.) endosperm mutants—shrunken-2 (sh2) and sugary (su)—were harvested 18 to 46 days postpollination (dpp). Mature sh2 seeds had a greater imbibition and leakage rate than did su. Leachate conductivity was greater from field-grown sh2 seeds than greenhouse-grown sh2 at maturity. No difference in carbohydrate leakage was observed between genotypes at maturity. Leakage generally decreased in all seed types with increasing maturity. Cracking of the pericarp was not noticeable in either sh2 or su during development. In mature seeds of both genotypes, the pericarp appeared to be thicker and adhered more tightly to the aleurone layer than in immature seeds. Dry seeds of sh2 contained considerably less total carbohydrates and starch than su 18 to 46 dpp. Field-grown su seeds accumulated more total carbohydrates during development than greenhouse-grown su or sh2. The lowest amounts of sugars in dry seeds occurred at maturity with no difference noted between field- and greenhouse-grown sh2 and field-grown su. Immature fresh kernels (freeze-dried) of su and sh2 contained 2 to 3 times, respectively, more sugars than immature dry kernels. At maturity, fresh and dry kernels of either genotype had equal amounts of sugars, but fresh kernels contained more starch.

Endosperm Type, Inbred Background, and Leakage of Seed Electrolytes During Imbibition in Sweet Corn

“…In comparing the endosperm types, Su sh2 had the highest SLEC values, which was 189% of the SLEC of Su du wx, the next highest endosperm type (Table 2). The high SLEC from su sh2 is consistant with previous reports (12,15,16). The endosperm type that exhibited the lowest SLEC was Su su2 (62.9 dS*m_1).…”

“…However, if the significant effects of years is due to seed aging, the response to aging varies according to both endosperm and inbred, as indicated by the significant interaction terms. Due to the established relationship between SLEC and seedling vigor, endosperm and inbred effects were expected based on results of previous studies in corn (12,(14)(15)(16)) and soybean (4). However, we have identified differences in SLEC over an expanded number of endosperm types.…”

“…The different proportion of endosperm constituents may result in differences in SLEC as reported here. However, a second factor involved in the SLEC differences may be the disruption of membranes and damage to the pericarp during the collapse of defective kernel types, such as Su sh2 (12). In addition to lighter w eigh t kernels, kernel collap se results in the separation of the pericarp from the endosperm.…”

“…Within the limited number of endosperm types examined, endosperm type has an effect on SLEC (12,15,16). Among three sweet corn hybrids, each with a different endosperm type, SLEC was greater from seed with endosperm genotypes sh2 or ae du wx ('Florida Staysweet' and 'Pennfresh ADX', respectively) than the su hybrid 'Iochief (15).…”

“…Recently, endosperm types including sh2, ae du wx, brittle (bt), and others have become important in the sweet corn industry (3). SLEC has been established as a rapid and accurate method of determining seed quality in maize (12,15,16). Due to seed quality problems associated with sh2, ae, du, wx, and bt endosperm types (2,3,9), it would be useful for sweet corn breeders and seedsmen to understand the factors that affect SLEC.…”