Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

Sources, Fluxes, and Sinks of Nitrogen during Early Reproductive Growth of Maize (Zea mays L.)

A study was designed to (a) identify sources and sinks of N in the maize (Zea mays L.) shoot, by estimating net N fluxes for each of seven parts of the shoot, (b) determine effects of N entering the plant upon fluxes of N absorbed before reproductive growth, and (c) determine the effects of the opaque-2 gene on N fluxes in the maize shoot during early reproductive growth. Plants of a maize hybrid (Pioneer 3369A) and its opaque-2 counterpart (Pioneer L3369) were grown in a greenhouse using nutrient solution/sand culture, with NO₃⁻ as the N source during the vegetative growth phase. Beginning at the time of pollination, the same nutrient regime was continued, except that some plants received no N, and others received 3.75 millimolar ¹⁵N as NO₃⁻-N.

Stalk and leaves were found to be primary N sources for the grain, while shank, husk, and cob acted first as N sinks, then as N sources during reproductive growth. Net fluxes of N for each plant part were estimated by calculating the first derivatives of regression equations used to fit data for N contents of each plant part as functions of time. All parts of the shoot were sinks for exogenous N (absorbed after pollination). Thirty-six days after pollination, the grain contained 60% endogenous N (absorbed before pollination) when 3.75 millimolar NO₃⁻-N was supplied after pollination. Rates of total N influx to the grain were identical whether or not N was supplied in the nutrient solution during reproductive growth. At 36 days after pollination, less N had accumulated in the grain of the opaque-2 genotype, but otherwise there were no differences in N contents or dry weights of the shoots due to the opaque-2 gene. Absence of N from the rooting medium significantly affected N fluxes throughout the shoot during reproductive growth, but there were no detectable effects of the opaque-2 gene on N fluxes in parts of the plant other than the grain.

     

Variation in the ribosomal internal transcribed spacers and 5.8S rDNA among five species of Acropora (Cnidaria; Scleractinia): patterns of variation consistent with reticulate evolution

The ITS sequences of Acropora spp. are the shortest so far identified in any metazoan and are among the shortest seen in eukaryotes; ITS1 was 70-80 bases, and ITS2 was 100-112 bases. The ITS sequences were also highly variable, but base composition and secondary structure prediction indicate that divergent sequence variants are unlikely to be pseudogenes. The pattern of variation was unusual in several other respects: (1) two distinct ITS2 types were detected in both A. hyacinthus and A. cytherea, species known to hybridize in vitro with high success rates, and a putative intermediate ITS2 form was also detected in A. cytherea; (2) A. valida was found to contain highly (29%) diverged ITS1 variants; and (3) A. longicyathus contained two distinct 5.8S rDNA types. These data are consistent with a reticulate evolutionary history for the genus Acropora.      

A survey of potato aphides in north-west Derbyshire, 1945

Counts of aphides infesting potato crops in north-west Derbyshire at altitudes between 340 and 1360 ft. were made during the summer of 1945. Mysus persicae was abundant on almost all crops, and peak figures on some reached over 1500 per 100 lower leaves. In many fields two peaks were noted, one towards the end of July and the second in mid-September, and in some fields there were still heavy infestations when the haulms died. The number of aphides varied considerably from field to field; sheltered fields were the least infested. In this area in 1945 there was no evidence to support the contention that the altitude and aspect of the field have any influence on the intensity of infestation. Tuber samples from six fields showed that there was a considerable spread of leaf roll.     

Genome –Scale Reconstruction of Metabolic Networks of Lactobacillus casei ATCC 334 and 12A

Lactobacillus casei strains are widely used in industry and the utility of this organism in these industrial applications is strain dependent. Hence, tools capable of predicting strain specific phenotypes would have utility in the selection of strains for specific industrial processes. Genome-scale metabolic models can be utilized to better understand genotype-phenotype relationships and to compare different organisms. To assist in the selection and development of strains with enhanced industrial utility, genome-scale models for L. casei ATCC 334, a well characterized strain, and strain 12A, a corn silage isolate, were constructed. Draft models were generated from RAST genome annotations using the Model SEED database and refined by evaluating ATP generating cycles, mass-and-charge-balances of reactions, and growth phenotypes. After the validation process was finished, we compared the metabolic networks of these two strains to identify metabolic, genetic and ortholog differences that may lead to different phenotypic behaviors. We conclude that the metabolic capabilities of the two networks are highly similar. The L. casei ATCC 334 model accounts for 1,040 reactions, 959 metabolites and 548 genes, while the L. casei 12A model accounts for 1,076 reactions, 979 metabolites and 640 genes. The developed L. casei ATCC 334 and 12A metabolic models will enable better understanding of the physiology of these organisms and be valuable tools in the development and selection of strains with enhanced utility in a variety of industrial applications.