No abstract

Juvenile hormone (JH) has central roles in the regulation of insect development and reproduction but has not previously been identified in other arthropod classes. The hemolymph of a crustacean, Libinia emarginata (Leach), has now been analyzed for JH-like compounds. Samples contained 0.003 to 0.030 nanogram of JH III per milliliter and 10 to 50 nanograms of methyl farnesoate per milliliter; methyl farnesoate is a compound structurally related to JH III that has JH bioactivity. Several tissues were examined for synthesis and secretion of JH-like compounds. Of these tissues, only the mandibular organs produced and secreted JH III and methyl farnesoate. However, microchemical analysis revealed that this JH III was racemic, and thus likely an artifactual oxidation product of methyl farnesoate. Secretion of methyl farnesoate was related to reproduction in females, with the highest rates observed in Libinia near the end of the ovarian cycle when oocyte growth and vitellogenesis are greatest. These results indicate that JH-like compounds such as methyl farnesoate have regulatory roles in crustaceans.

The in vitro production of juvenile hormone (JH) was investigated by using isolated ring glands from third instar Drosophila melanogaster. A JH-like molecule is secreted that comigrates with a synthetic sample of methyl 6,7;10,11-bisepoxy-3,7,11-trimethyl-(2E)-dodecenoate (JHB3) during TLC, liquid chromatography, and GC analysis. Purified product from farnesoic acid-stimulated ring glands was analyzed by electron impact GC/MS and gave a mass spectrum identical to synthetic JHB3. Additional structure confirmation was obtained following conversion of product from unstimulated biosynthesis to a derivative that comigrated on liquid chromatography with the derivative prepared from synthetic JHB3. Physiological studies revealed that JHB3 is produced solely by the corpus allatum portion of the ring gland in vitro. Isolated ring glands from other cyclorrhaphous dipteran larvae also produce JHB3 almost exclusively in vitro. Corpora allata from mosquito larvae, however, produce only JH III, indicating that JHB3 production may be restricted to the higher Diptera. Topically applied synthetic JHB3 caused developmental responses in newly formed D. melanogaster white puparia similar to those obtained with JH III. The data suggest that JHB3 is a fly juvenile hormone.

When Lemna minor L. is supplied with the potent inhibitor of glutamine synthetase, methionine sulfoximine, rapid changes in free amino acid levels occur. Glutamine, glutamate, asparagine, aspartate, alanine, and serine levels decline concomitantly with ammonia accumulation. However, not all free amino acid pools deplete in response to this inhibitor. Several free amino acids including proline, valine, leucine, isoleucine, threonine, lysine, phenylalanine, tyrosine, histidine, and methionine exhibit severalfold accumulations within 24 hours of methionine sulfoximine treatment. To investigate whether these latter amino acid accumulations result from de novo synthesis via a methionine sulfoximine insensitive pathway of ammonia assimilation (e.g. glutamate dehydrogenase) or from protein turnover, fronds of Lemna minor were prelabeled with I'5NIH.4, prior to supplying the inhibitor. Analyses of the 'IN abundance of free amino acids suggest that protein turnover is the major source of these methionine sulfoximine induced amino acid accumulations. Thus, the pools of valine, leucine, isoleucine, proline, and threonine accumulated in response to the inhibitor in the presence of [I5NIH4', are '4N enriched and are not apparently derived from '5N-labeled precursors. To account for the selective accumulation of amino acids, such as valine, leucine, isoleucine, proline, and threonine, it is necessary to envisage that these free amino acids are relatively poorly catabolized in rivo. The amino acids which deplete in response to methionine sulfoximine (i.e. glutamate, glutamine, alanine, aspartate, asparagine, and serine) are all presumably rapidly catabolized to ammonia, either in the photorespiratory pathway or by alternative routes.It is now well established that GS2 occupies a central position in plant N metabolism (12, 13). The GS-GOGAT cycle is thought to be responsible for the assimilation of most, if not all, of the ammonia derived from nitrate reduction and photorespiration (2-4, 10, 18, 19, 21, 23, 25). Studies with the potent inhibitor of GS, MSO, appear to rule out any major contribution of GDH to ammonia assimilation (1,3,8,19,21,23). However, recent investigations with isolated plant mitochondria suggest that a small fraction of the ammonia generated from glycine decarboxylation can be directly reassimilated into glutamic acid via a mitochondrial GDH (26). The quantitative significance of this latter pathway in vivo still remains obscure. '

ABSTRACIA rapid, sensitive, and selective method for the determination of betaines is described and discussed. The method entails derivatizing the quaternary ammonium compounds to increas their sensitivity to detection by fast atom bombardment mass spectrometry. Sensitivity of detection increases markedly as the length of the carbon chain of the alcohol used to esterify the betaine carboxylic acid group is inreased (C4 > C3 > C2 > Cl > Ca). The lower limit of detection of glycine betaine as the i-propyl ester is 0.05 nanomole per microliter of glycerol. Betaine aldehyde can be readily derivatized to the di-n-butyl or di-n-propyl acetal derivatives which exhibit lower limits of detection of about 5 picomoles and 10 picomoles per microliter of glycerol respectively. Accurate quantification of these compounds is accomplished by the use of deuterium labeled internal stanards or quaternary ammonium compound homologs of distinct mass. Methods for the synthesis of these internal standards are reported. Some applications of these methods are iflustrated with stable isotope tracer studies on the kinetics of metabolism of choline to betaine aldehyde and glycine betaine in spinach leaf discs, and the identification of several Zea mays genotypes which appear deficient in glycine betaine. Tracer studies with deuterium labeled betaine aldehyde suggest that the deficiency of glycine betaine in one sweet corn hybrid is probably not due to a deficiency in the capacity to oxidize betaine aldehyde.Quaternary ammonium compounds occur widely in nature and may serve important roles as compatible osmotic solutes or osmoprotectants (13,17,22,(28)(29)(30)34). Glycine betaine (N,N, N-trimethyl glycine) is thus of considerable interest in terms of the osmotic stress tolerance of the Chenopodiaceae and Gramineae (7, 15-18, 20, 32, 33). But a key test of the adaptive significance of glycine betaine accumulation in osmoregulation in higher plants must ultimately come from the identification and detailed characterization ofglycine betaine deficient mutants of glycine betaine accumulating species (16,17 In considering screening maize germplasm for genotypic differences in glycine betaine levels, and potential methods for characterizing putative betaine null genotypes, we noted a paucity ofconvenient methods which would lend themselves to both accurate quantification of low glycine betaine levels in the presence of other quaternary ammonium compounds (e.g. choline, phosphoryl-choline, and betaine aldehyde) and stable isotope tracer studies on the betaine biosynthetic pathway. Available methods for betaine determination lack either sensitivity, resolution, and/or amenability to stable isotope tracer work (4, 8, 12-14, 19, 20). We therefore sought sensitive mass spectral methods for quantifying glycine betaine and its stable isotope abundance.Mass spectral analysis of quaternary ammonium compounds of synthetic and natural origin has been approached for the most part by desorption methods. FABMS2 (6), 252Cf fission-fragment and laser desorption (...