Date of Award:

5-1-1992

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology (Molecular Biology)

Committee Chair(s)

Elizabeth E. Hood

Committee

Elizabeth E. Hood

Committee

Anne Anderson

Committee

Jennifer MacAdam

Abstract

Extensin is a major cell wall structural protein found in both dicotyledonous and monocotyledonous plants that functions in cell wall support and putatively plays a role in plant defense. The purpose of this study was to demonstrate the molecular basis for the protein size heterogeneity of extensin from silk and pericarp tissues of two varieties of maize, Japanese Hulless Popcorn (JHL) and Golden X Bantam (GXB), a sweet corn. JHL and GXB differ in thickness of their pericarp. JHL pericarp is thicker and aids in water retention, which is important for popping. Extensin isolated from GXB has an apparent molecular weight of 66 kD based on SDS-polyacrylamide gel electrophoresis. In contrast, extensins isolated from JHL are of two molecular weights, 66 and 76 kD. Deglycosylation with anhydrous hydrogen fluoride treatment reduces the molecular weight of mature extensins from both JHL and GXB by 5 kD. Northern blot analysis, using a 500 bp maize extensin genomic clone as a probe, demonstrates the existence of two transcripts (1.9 and 1.5 kb) from JHL pericarp and silk RNA. GXB pericarp and silk RNA contain only the 1.5 kb transcript. The maize extensin genomic clone also hybridizes to two larger transcripts, 6.2 and 4.5 kb, which are present in both varieties. Immunoprecipitation of in vitro translation products with monoclonal antibodies raised against GXB extensin results in two proteins, 56 and 66 kD, from JHL messenger RNA, and one protein, 56 kD, from GXB mRNA. These results confirm that the size difference in extensin between these two varieties is due to a larger protein backbone. Additionally, these results suggest that more than one species of maize extensin exists in JHL and that the peptides are most likely encoded by different messenger RNAs.

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