REGULATION OF STORAGE PROTEIN SYNTHESIS IN ZEIN-DEFICIENT MAIZE MUTANTS

LISA LEE, Purdue University

Abstract

In the developing endosperm of maize (Zea mays L.), total protein increased throughout development in the normal genotype. However, the mutant endosperms (opaque-2, brittle-2, brittle-1, brittle-2 opaque-2, and brittle-1 opaque-2) contained less protein than did the normal genotype. This reduction was mainly due to a decreased zein accumulation. Starch-deficient maize mutants, such as shrunken-2, that accumulated large quantities of sucrose, generated a more negative osmotic potential. This favored water movement but reduced solute movement into the mutant endosperm. Thus, the mutant kernels absorbed only about 25% as much of the labeled amino acids as did the normal kernels. The inability of amino acids to move into the mutant kernels in part explained the reduction of storage protein synthesis in the starch-deficient mutant endosperms. A post-transcriptional degradation of zein mRNAs presumably caused by a high RNase activity also may be involved in reducing zein synthesis in the zein-deficient mutants. A highly significant negative correlation was observed between the zein content and the RNase levels. Zein proteins prepared from mature endosperms of the double mutants such as brittle-2 opaque-2 and brittle-1 opaque-2 showed almost completely blockage of the synthesis of two major zein compounds, Z1 and Z2. However, these two components were present prior to 12 days post-pollination. The changes in quantity and quality of zein synthesis in these double mutants correlated well with the rising RNase levels in the developing endosperm. In contrast to the endosperm, the brittle-2 opaque-2 embryo produced amounts of zein and its electrophoretic pattern similar to that of the opaque-2 embryos. Also, the brittle-2 opaque-2 embryo contained sucrose levels and RNase activity comparable to that found in normal embryos. In addition to its effect on zein synthesis, high RNase activity also influenced the stability of rRNAs in the brittle-2 opaque-2 mutant. The cessation of glutelin synthesis at the later stages of development also coincided with rRNA degradation. These results suggest that RNase played a role in regulating zein synthesis in developing zein-deficient mutant endosperms.

Degree

Ph.D.

Subject Area

Genetics

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