Conservation and duplication of isozymes in plants

Evidence for an intra- and extraplastidic pre-chorismate pathway

Pea plants grown under different conditions of cultivation, and eight different plant species with variegated leaves were used to study the intracellular localization of shikimate oxidoreductase (EC 1.1.1.25), the marker enzyme of the pre-chorismate pathway. The two series of experiments indicated an intra-and an extraplastidic compartimentalization of the enzyme, and both enzyme activities are regulated differentially. While the extraplastidic activity is permanently demonstrable, the intraplastidic activity is subject to the plants' developmental state and also depends on both illumination and fertilization.

Differential regulation of duplicate alcohol dehydrogenase genes in Drosophila mojavensis

These studies report the existence of multiple forms of alcohol dehydrogenase in extracts of Drosophila mojavensis. The existence of these forms can be best explained by the hypothesis of a duplication for the Adh locus in D. mojavensis. Electrophoretic variants at each locus have been identified and crosses between individuals carrying alternative alleles at each locus result in F1 progeny with six bands of ADH. This pattern is consistent with these individuals being heterozygous at two loci. The loci have been named Adh-1 and Adh-2. Examination of the isozyme content during development shows that the two Adh genes are not coordinately controlled but have separate developmental programs. In embryos and first and second instar larvae only Adh-1 is expressed. At about the time of the second molt Adh-2 expression commences in some of the same cells that previously expressed and continue to express Adh-1. This is evidenced by the existence of an interlocus heterodimer in third instar larvae. Both genes are expressed throughout pupation. Shortly after emergence Adh-1 expression declines. In mature males only ADH-2 is present. In mature females both Adh-1 and Adh-2 are expressed but not in the same cells since the interlocus heterodimer is absent. Examination of specific tissues reveals that most of the larval ADH is found in fat body cells and as in most tissues of third instar larvae both Adh-1 and Adh-2 are expressed. The single exception appears to be larval gut which contains ADH-1 but little if any ADH-2. In mature males and female flies all ADH containing tissues have only ADH-2. However, mature ovaries contain substantial quantities of ADH-1 which is apparently deposited into eggs. Given the extensive amount of available information on the Adh gene-enzyme system of D. melanogaster and the tools that can be applied to the analysis of homologous systems, the ADH duplication of D. mojavensis, and its regulation may be a useful one for studying differential gene regulation in specific cell types.

Isolation of Agronomically Useful Mutants from Plant Cell Cultures

Enormous genetic variability is accumulated by plant cells proliferating in culture. Additional variability can be induced in cultured cell populations by exposure to mutagens. This pool of genetic diversity can be examined for agronomically desirable traits at two levels of differentiation. Populations of plants regenerated from callus cultures can be screened by conventional methods. Alternatively, selective culture conditions favoring growth of specific mutant types can be applied at the cellular level. The several characteristics that have been introduced by these methods to date are a harbinger of future contributions to be made by cell culture to the genetic improvement of crops.

Alcohol dehydrogenase isozymes in grain sorghum (Sorghum bicolor): evidence for a gene duplication

Two sets of alcohol dehydrogenase (ADH) bands are regularly observed in grain sorghum (Sorghum bicolor): set I is a permanent triplet; set II is variable, as either two or three bands. A faint set III is detected only when extracts from seeds subjected to anaerobiosis are run in neutral pH gels. Dissociation-reassociation experiments reveal that the central band of the set I triplet is a heterodimer of the other two. Full-sib progeny analysis from self-fed plants shows that the set II bands are doublets, with heterozygotes having only three apparent bands instead of four because of the similar mobilities of the fast-migrating isozyme specified by the slow allele and the slow isozyme specified by the fast allele. We propose a three-locus model as the best explanation of these patterns. Set I consists of the products of two loci and their intergenic heterodimer. Set III is specified by a third locus. Set II isozymes are the intergenic heterodimers of the two set I loci and the set III locus. This explanation is similar to that of Schwartz and Freeling for maize but suggests that the evolution of Sorghum includes a gene duplication of the homologue of the Adh-1 locus in Zea.