Biomedical subjects
Publications and source records attributed to G L Stebbins.
A brief summary of my current ideas on evolution is presented. Three recent books that represent important synopses of evolution are considered in the discussion. Differences between plants and animals that have important implications for evolution in the two groups are discussed. Progress in understanding plant evolution requires synthetic studies integrating data from many different areas of research.
The DNA sequences for 17 plant genes for alpha-amylase (EC 3.2.1.1) were analyzed to determine their phylogenetic relationship. A phylogeny for these genes was obtained using two separate approaches, one based on molecular clock assumptions and the other based on a comparison of sequence polymorphisms (i.e., small and localized insertions) in the alpha-amylase genes. These polymorphisms are called "alpha-amylase signatures" because they are diagnostic of the gene subfamily to which a particular alpha-amylase gene belongs. Results indicate that the cereal alpha-amylase genes fall into two major classes: AmyA and AmyB. The AmyA class is subdivided into the Amy1 and Amy2 subfamilies previously used to classify alpha-amylase genes in barley and wheat. The AmyB class includes the Amy3 subfamily to which most of the alpha-amylase genes of rice belong. Using polymerase chain reaction and oligonucleotide primers that flank one of the two signature regions, we show that the AmyA and AmyB gene classes are present in approximately equal amounts in all grass species examined except barley. The AmyB (Amy3 subfamily) genes in the latter case are comparatively underrepresented. Additional evidence suggests that the AmyA genes appeared recently and may be confined to the grass family.
One of the principles that has emerged from experimental evolutionary studies of microorganisms is that polymorphic alleles or new mutations can sometimes possess a latent potential to respond to selection in different environments, although the alleles may be functionally equivalent or disfavored under typical conditions. We suggest that such responses to selection in microorganisms serve as experimental models of evolutionary advances that occur over much longer periods of time in higher organisms. We propose as a general evolutionary principle that anagenic advances often come from capitalizing on preexisting latent selection potentials in the presence of novel ecological opportunity.
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Reproductive meristems of the hooded (KK) genotype of barley at the stage of young lemma primordia were injected with the inhibitors sodium azide, hydrazine, and hydroxylamine at concentrations of 10(-3), 10(-4), and 10(-5)M, as well as with phenylboric acid. These treatments all brought about an altered expression of the adult phenotype in the direction of awned (kk) genotype. Analysis of tissues treated with the same reagents revealed a reduction in peroxidase activity which was proportional to the effect of each inhibitor in modifying the phenotypic expression of the gene. Exogenous IAA injected in the same manner brought about a similar modification of the phenotype and parallel reduction of peroxidase activity, but to a lesser degree. These results are believed to be caused by modifications of the action of the IAA oxidase system in the developing meristems.
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