Hirofumi Uchimiya

A novel MT gene of rice plants is strongly expressed in the node portion of the stem.

We identified a cDNA encoding a metallothionein (MT)-like protein from a cDNA library of rice endosperm. This cDNA (ricMT) encoded an open reading frame of 80 amino acids, with two cysteine-rich domains at the amino-terminus and carboxy-terminus, respectively. The deduced amino acid sequence was homologous to those of class I MT-like proteins. Southern blot analysis revealed that the gene exists at one locus in the rice genome. Northern blot analysis with rice seedlings showed that the transcript level in shoots was elevated by the addition of metal ions, such as Cu, Zn, Cd, Fe, Pb and A1, whereas in roots it was reduced in the presence of metal ions other than copper. The expression level of ricMT in mature rice plants was extremely high in stems relative to leaf blades, leaf sheaths, endosperm and roots. In the first nodes, the yield of the transcript was 150-times higher than that in leaf blades. These results suggest that ricMT protein may play an important role in the metabolism of metal elements in the stem.

Genetic analyses of the formation of the serrated margin of leaf blades in Arabidopsis: combination of a mutational analysis of leaf morphogenesis with the characterization of a specific marker gene expressed in hydathodes and stipules.

Abstract Developmental control of the formation of the serrated margin of leaf blades was investigated. First, the expression was characterized of a marker gene encoding β-glucuronidase in strain #1-35-38, a transgenic strain of Arabidopsis thaliana (L.) Heynh, derived by the use of a previously described transposon-tagging system. In strain #1-35-38, expression of the marker gene was tissue-specific, being restricted to stipules and the toothed margins of laminae. Using this transgenic marker gene, we examined the development of leaf blade margins in Arabidopsis. We compared the pattern of expression of the marker gene in the leaves of the wild-type plant with that in plants carrying the asymmetric leaves1 (as1) mutation, which causes dramatic changes in leaf-blade morphology in Arabidopsis. The as1 mutant showed normal morphology of early leaf primordia. The mutation affected the development of leaf segmentation in Arabidopsis without any change in the number or morphology of cells in laminae. The as1 mutation affected leaf morphology independently of mutations in other genes known to affect leaf morphogenesis, such as the acaulis1 mutation and the angustifolia mutation. Based upon these results, the development of the morphology of leaf margins in Arabidopsis is discussed.

Phosphorylation of the C2 subunit of the proteasome in rice (Oryza sativa L.)

© 1997 Federation of European Biochemical Societies.

Molecular and biochemical characterization of a proteasome subunit from rice and carrot cells

Abstract Proteasomes function mainly in the ATP-dependent degradation of proteins that have been conjugated with ubiquitin. We isolated a cDNA clone for a rice protein that exhibited high homology to subunit C2 of proteasomes. Southern blot analysis revealed that the corresponding gene was present as a single copy in the rice genome. After fractionation of a crude extract from cultured cells, a 35-kDa protein that cross-reacted with antibodies against the C2 subunit was recovered in the peak fraction of both 20u2009S and 26u2009S complexes. The same antibodies cross-reacted with two proteins in seedlings, one of which was the same as that detected in cultured cells. The level of the protein was reduced in roots under conditions of high salinity. The 35-kDa protein was not detected in the nuclei of rice or carrot cells. However, during somatic embryogenesis of carrot cells, the C2 subunit was found in the nucleus at the globular stage, and it gradually disappeared in the period from the heart to the torpedo stage. Cells at the globular stage are proliferating rapidly, thus, it is possible that proteasomes are associated with the proliferation of plant cells.

Stimulation of adenylate kinase in rice seedlings under submergence stress

Summary The enzymatic activity of adenylate kinase was stimulated in submerged rice seedlings. This activity was enhanced in every organ of the submerged plants. Treatment with N 2 gas had the same effect as submergence, a result which suggests that O 2 -depletion is a major cause of the stimulation of adenylate kinase activity. Northern blot analysis also indicated accumulation of adenylate kinase mRNA under submerged condition. Furthermore, different induction patterns of enzymatic activity were seen in two rice varieties, FR13A and IR42, which are respectively tolerant and intolerant of complete submergence.