CHANGES IN CARBOHYDRATE-COMPOSITION AND ALPHA-AMYLASE EXPRESSION DURING GERMINATION AND SEEDLING GROWTH OF STARCH-DEFICIENT ENDOSPERM MUTANTS OF MAIZE

Kernels of 28 different maize (Zea mays L.) genotypes consisting of se veral inbreds isogenic for the starch-deficient endosperm mutations su gary1 (su1), sugaryl sugary enhancer1 (su1se1), and shrunken2 (sh2) we re used to study the effect of these mutations on carbohydrate composi tion and alpha-amylase expression during germination and seedling grow th in comparison to normal starchy kernels (Su). Sugar (fructose, gluc ose, sucrose, and maltose), WSP (water-soluble polysaccharide), and in soluble starch contents were determined for endosperm and scutellar ti ssues for each of the genotypes at four stages of seedling development . While initial levels of endosperm sucrose were higher in the endospe rm mutants, they rapidly declined by radicle emergence and remained lo w thereafter. Mobilization of carbohydrate reserves was most reduced i n the sh2 genotypes. Collectively, these factors represent a limited c arbon supply for the developing sh2 seedling which may impact seedling vigor. A more significant negative correlation was observed between p ercentage germination and endosperm sugar content than between percent age germination and scutellar sugar content. High initial levels of en dosperm sucrose in the mutants correlate with a severe reduction of al pha-amylase (EC 3.2.1.1) transcript abundance. The same correlation do es not hold for glucose and maltose, as at later stages of germination , levels were significantly higher in the Su genotype while the alpha- amylase mRNA levels remained high. Furthermore, the ratio of alpha-amy lase enzyme activity to transcript abundance was considerably lower in the sh2 aleurone compared to the Su aleurone at radicle emergence. Ge notype specific differences in alpha-amylase gene expression strongly correlate with endosperm sugar content and composition during germinat ion. (C) 1997 Elsevier Science Ireland Ltd.