บทคัดย่องานวิจัย

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Alpha-Amylases in shrunken-2 (sh2) and sugary enhancer (sul se) kernels of maize during germination

Sanwo, Monica M

Ph.D., University of California, Riverside, 1993, 160 pages

1993

บทคัดย่อ

ALPHA-AMYLASES IN SHRUNKEN-2 (SH2) AND SUGARY ENHANCER (SUL SE) KERNELS OF MAIZE DURING GERMINATION.

The shrunken-2 (sh2) and sugary-1, sugary enhancer (su1 se) sweet corn cultivars have high levels of kernel sugars and excellent postharvest qualities, but exhibit poor seed germination.  Studies were undertaken to identify possible causes for the poor seed germination in these cultivars.  Using alpha-amylase as a marker of cellular function, the aleurone and scutellum of sh2 and su1 se kernels were compared to Starchy (Su) kernels during germination, using alpha-amylase enzyme assays, isoelectric focusing (IEF) gels, TEM and confocal microscopy.  The aleurone tissues of sh2 kernels (Illini Xtra Sweet and RB-3) were deficient in alpha-amylase activity, and no alpha-amylase isozymes could be detected on IEF gels using starch zymograms or immunoblots probed with alpha-amylase antibodies.  TEM and confocal microscopy analyses of the Su (Funks G4646) aleurone cells revealed abundant RER, cytoplasmic membranes and RNA, but the sh2 (Illini Xtra Sweet) aleurone contained mostly lipid and protein bodies

  at 7 d after imbibition.  The absence of RER, cytoplasmic membranes and RNA in the sh2 aleurone suggests an impaired capacity for protein synthesis.  Exogenous applications of GA3 (0.001-10 muM) induced alpha-amylase activity, the occurrence of isozymes on IEF gels, and alpha-amylase mRNA accumulation in the sh2 aleurone (RB-3), but levels were lower than that of the Su (RB-4) aleurone.  With confocal microscopy, a partial restoration of cellular structure was observed in the GA3-treated sh2 aleurone.  The 1.0 muM GA3 treatment induced shoot elongation in the sh2 seedlings, but other aspects of seedling growth were not significantly affected.  In the su1 se cultivar Illinois 677a, there were low levels of alpha-amylase activity in the scutellum and fewer alpha-amylase isozymes (4) than the Funks G4646 (Su) scutellum (8).  A comparison of alpha-amylase isozyme profiles in selected Su, su1, sh2 and su1 se lines revealed differences in the number of isozymes in the aleurone and scutellum tissues of these kerne

 ls, ranging from 0 isozymes in the RB-3 (sh2) aleurone to 15 isozymes in the IL451b (Su) aleurone, indicating that genotype, tissue and genetic background influence the synthesis of multiple isozymes in maize.  The deficiency in alpha-amylases in the aleurone of sh2 and the scutellum of su1 se kernels suggests impaired metabolic function, which could result in delayed mobilization of storage reserves and contribute to poor germination.