Nucleotides and Nucleotide Sugars in Developing Maize Endosperms (Synthesis of ADP-Glucose in brittle-1)

As part of an in vivo study of carbohydrate metabolism during development of Zea mays L. kernels, quantities of nucleotides and nucleotide sugars were measured in endosperm extracts from normal, the single-mutant genotypes shrunken-1 (sh1), shrunken-2 (sh2), and brittle-1 (btl}, and the multiple-mutant genotypes sh1bt1, sh2bt1, and sh1sh2bt1. Results showed that bt1 kernels accumulated more than 13 times as much adenosine 5[prime] diphospho-glucose (ADP-Glc) as normal kernels. Activity of starch synthase in bt1 endosperm was equal to that in endosperm extracts from normal kernels. Thus the ADP-Glc accumulation in bt1 endosperm cells was not due to a deficiency in starch synthase. ADP-Glc content in extracts of sh1bt1 endosperms was similar to that in bt1, but in extracts of the sh2bt1 mutant kernels ADP-Glc content was much reduced compared to bt1 (about 3 times higher than that in normal). Endosperm extracts from sh1sh2bt1, kernels that are deficient in both ADP-Glc pyrophosphorylase (AGPase) and sucrose synthase, had quantities of ADP-Glc much lower than in normal kernels. These results clearly indicate that AGPase is the predominant enzyme responsible for the in vivo synthesis of ADP-Glc in bt1 mutant kernels, but Suc synthase may also contribute to the synthesis of ADP-Glc in kernels deficient in AGPase.     

Invertebrate phosphatidylinositol-specific phospholipases C and their role in cell signaling

Phosphatidylinositol-specific phospholipase C (PLC) is a family of enzymes that occupy a pivotal role in one of the largest classes of cellular signaling pathways known. Mammalian PLC enzymes have been divided into four major classes and a variety of subclasses based on their structural characteristics and immunological differences. There have been five invertebrate PLC-encoding genes cloned thus far and these fall within three of the four major classes used in categorizing mammalian PLC. Four of these invertebrate genes have been cloned fromDrosophila melanogaster and one is fromArtemia, a brine shrimp. Structural characteristics of the invertebrate enzymes include the presence of highly conserved Box X and Box Y domains found in major types of mammalian PLC as well as novel features. Two of the invertebrate PLC genes encode multiple splice-variant subtypes which is a newly emerging level of diversity observed in mammalian enzymes. Studies of the invertebrate PLCs have contributed to the identification of the physiological functions of individual isozymes. These identified roles include cellular processes such as phototransduction, olfaction, cell growth and differentiation.     

The effect of temperature on the degradation of triglycerides by a pseudomonad isolated from milk: free fatty acid accumulation as a balance between rates of triglyceride hydrolysis and fatty acid consumption

The lipolysis of triglyceride by a lipolytic pseudomonad, LS107d2, and the net levels of free fatty acids (FFA) in milk cultures of LS107d2 have been studied as a function of temperature. The metabolism of triolein results in the accumulation of oleic acid at 4°C but, at higher temperatures, triolein is hydrolysed without detectable oleate accumulation. Temperature also has a profound effect on the levels of FFA in whole milk cultures of LS107d2, and on the temporal pattern of changes in FFA levels. The results are consistent in demonstrating that FFA consumption plays a significant role in determining the net level of FFA in milk, even in the presence of very high rates of lipolysis. Thus the net levels of FFA as a result of the growth of LS107d2 in milk are the result of a dynamic balance between rates of FFA production (by lipolysis) and subsequent consumption. Temperature can dramatically affect the levels of FFA in milk cultures, and these changes are proposed to be due to opposing influences on FFA consumption and production, affecting the balance between them.     

Control of Internode Length in Pisum sativum (Further Evidence for the Involvement of Indole-3-Acetic Acid)

The effects of altered endogenous indole-3-acetic (IAA) levels on elongation in garden pea (Pisum sativum L.) plants were investigated. The auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and 9-hydroxyfluorene-9-carboxylic acid (HFCA) were applied to elongating internodes of wild-type and mutant lkb plants. The lkb mutant was included because elongating lkb internodes contained 2- to 3-fold less free IAA than those of the wild type. In the wild type, TIBA reduced both the IAA level and internode elongation below the site of application. Both TIBA and HFCA strongly promoted the elongation of lkb internodes and also raised IAA levels above the application site. The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) also markedly increased internode elongation in lkb plants and virtually restored petioles and tendrils to their wild-type length. In contrast, treatment of wild-type plants with TIBA, HFCA, or 2,4-D caused little or no increase in elongation above the application site. The ethylene synthesis inhibitor aminoethoxyvinylglycine also increased stem elongation in lkb plants, and combined application of HFCA and aminoethoxy-vinylglycine restored lkb internodes to the wild-type length. It is concluded that the level of IAA in wild-type internodes is necessary for normal elongation, and that the reduced stature of lkb plants is at least partially attributable to a reduction in free IAA level in this mutant.     

Elucidation of the mechanism of CryIIIA overproduction in a mutagenized strain of Bacillus thuringiensis var. tenebrionis

NB176 is a Bacillus thuringiensis mutant derived by λ-irradiation of NB125 Bacillus thuringiensis var. tenebrionis (Krieg). It exhibits two interesting phenotypes: (i) oligosporogeny and (ii) twofold to threefold overproduction of the CryIIIA protein. Southern profiles of the NB176 strain showed an additional copy(s) of the cryIIIA gene located on a 4 kb HindIII fragment, in addition to the expected cryIIIA gene on a 3 kb HindIII fragment. Each cryIIIA gene-bearing HindIII fragment was cloned from NB176. The restriction map of the 3 kb HindIII fragment was identical to that published by Donovan and coworkers. Sequencing of the 4 kb HindIII fragment showed no alterations in the promoter region of the cryIIIA gene but did show replacement of the region immediately following the cryIIIA open reading frame with a sequence encoding a transposase with 50% amino acid homology to that of Tn 1000. These findings suggest that the overproduction phenotype of NB176 results from extra copies of the cryIIIA gene produced from a transposition event(s) induced or stabilized by γ-irradiation. Integration of additional copies of the cryIIIA gene into the native 90MDa plasmid of the wild-type B. thuringiensis var. tenebrionis strain resulted in strains that made enormous crystals, many possessing greatly enhanced insecticidal activity.     

The human glucagon receptor encoding gene: structure, cDNA sequence and chromosomal localization

Characterization of the human glucagon-receptor-encoding gene (GGR) should provide a greater understanding of blood glucose regulation and may reveal a genetic basis for the pathogenesis of diabetes. A cDNA encoding a complete functional human glucagon receptor (GGR) was isolated from a liver cDNA library by a combination of polymerase chain reaction and colony hybridization. The cDNA encodes a receptor protein with 80% identity to rat GGR that binds [¹²⁵I] glucagon and transduces a signal leading to increases in the concentration of intracellular cyclic adenosine 3′,5′-monophosphate. Southern blot analysis of human DNA reveals a hybridization pattern consistent with a single GGR locus. In situ hybridization to metaphase chromosome preparations maps the GGR locus to chromosome 17q25. Analysis of the genomic sequence shows that the coding region spans over 5.5 kb and is interrupted by 12 introns.     

Genetic relationships of Brachygobius and related brackish Indo-west Pacific and Australasian genera (Teleostei: Gobiidae)

Horizontal starch gel electrophoresis was employed to analyse genetic variation, at 19 isozyme loci, in six putatively related species of gobies ( Brachygobius aggregatus, B. doriae, Pandaka lidwilli, Pseudogobius olorum, Pseudogobius sp. and Redigobius sp.), using seven other gobiine species as an outgroup. Allozyme data was analysed both cladistically and phenetically, all treatments confirming the monophyly of the group. Pandaka is confirmed as the sister genus to Brachygobius , these genera forming a crown group, with Redigobius and Pseudogobius forming successive sister groups. This scenario is in agreement with morphological hypotheses of phylogeny. However, this lineage appears to be relatively unrelated to other groups within the Gobiinae