Yet Another Interpretation of the Coelacanthiform Basicranial Muscle and its Innervation

Abstract A compilation of newly published information on the innervation of the basicranial muscle in the living tufttail Latimeria chalumnae and data obtained from other craniates, extant as well as extinct, suggest that the coelacanthiform basicranial musculature and the nerve supply which pertains to it are trimetameric in character rather than monometameric, as usually reported. This result supports the available data on the basic composition of the head of craniate animals and gives no support to a recently suggested homology between the tufttail basicranial muscles and the tetrapod retractor bulbi musculature.     

Insertion of Transposon Tn917 Derivatives into the Lactococcus lactis subsp. lactis Chromosome

Two transposition vectors, pTV32 and pLTV1, containing transposon Tn917 derivatives TV32 and LTV1, respectively, were introduced into Lactococcus lactis subsp. lactis MG1614. It was found that pTV32 and pLTV1 replicate and that TV32 and LTV1 transpose in this strain. A protocol for production of a collection of Tn917 insertions in L. lactis subsp. lactis was developed. The physical locations of TV32 on the chromosomal SmaI fragments of 62 independent transpositions were established by pulsed-field gel electrophoresis. These transpositions could be divided into at least 38 different groups that exhibited no Tn917-dominating hot spots on the L. lactis subsp. lactis chromosome. A total of 10 of the 62 transpositions resulted in strains that express β-galactosidase. This indicates that there was fusion of the promoterless lacZ of the Tn917 derivatives to a chromosomal promoter. Thus, the Tn917-derived transposons should be powerful genetic tools for studying L. lactis subsp. lactis.     

Molecular cut-off values of dialysis membranes for alginate and kappa-carrageenan oligosaccharides

The effective molecular weight cut-off values of dialysis membranes for carrageenan and alginate oligosaccharides were evaluated by gel permeation chromatography and nuclear magnetic resonance spectroscopy. For the different membranes tested, i.e. Medicell, Spectra Por 1000D and 3500D, the porous sizes are analogous to tri- and tetrasaccharides. A simple dialysis can be used to recover the majority of the oligosaccharides produced by a carrageenase or an alginate lyase digestion.     

Internodal elongation and orientation of cellulose microfibrils and microtubules in deepwater rice

Excised stem sections of deepwater rice (Oryza sativa L.) containing the highest internode were used to study the induction of rapid internodal elongation by gibberellin (GA). It has been shown before that this growth response is based on enhanced cell division in the intercalary meristem and on increased cell elongation. In both GA-treated and control stem sections, the basal 5-mm region of the highest internode grows at the fastest rate. During 24 h of GA treatment, the internodal elongation zone expands from 15 to 35 mm. Gibberellin does not promote elongation of internodes from which the intercalary meristem has been excised. The orientation of cellulose microfibrils (CMFs) is a determining factor in cell growth. Elongation is favored when CMFs are oriented transversely to the direction of growth while elongation is limited when CMFs are oriented in the oblique or longitudinal direction. The orientation of CMFs in parenchymal cells of GA-treated and control internodes is transverse throughout the internode, indicating that CMFs do not restrict elongation of these cells. Changes in CMF orientation were observed in epidermal cells, however. In the basal 5-mm zone of the internode, which includes the intercalary meristem, CMFs of the epidermal cell walls are transversely oriented in both GA-treated and control stem sections. In slowly growing control internodes, CMF orientation changes to the oblique as cells are displaced from this basal 5-mm zone to the region above it. In GA-treated rapidly growing internodes, the reorientation of CMFs from the transverse to the oblique is more gradual and extends over the 35-mm length of the elongation zone. The CMFs of older epidermal cells are obliquely oriented in control and GA-treated internodes. The orientation of the CMFs parallels that of the cortical microtubules. This is consistent with the hypothesis that cortical microtubules determine the direction of CMF deposition. We conclude that GA acts on cells that have transversely oriented CMFs but does not promote growth of cells whose CMFs are already obliquely oriented at the start of GA treatment.     

Neutral gravitaxis of gliding Loxodes exposed to normal and raised gravity

Summary In the statocystoid-bearing, flat ciliate Loxodes, the peculiar steady locomotion on submersed substrates (called gliding) was investigated between 1 g and 5.4 g under controlled environmental conditions in a centrifuge microscope. Videorecordings of the movements of large cell populations were processed with an automated analysis procedure. At 1 g, possible sedimentation was fully compensated, and vertical shifts of the population were neutralized because upward and downward orientations of the cells occurred at equal proportions (neutral gravitaxis). With rising gravity the resultant velocity of upward-gliding cells remained unchanged, whereas the velocity of downward-gliding cells increased continuously. Long-term exposure to hypergravity did not generate detectable signs of adaptation. The bipolar orientation of Loxodes persisted even under fivefold normal gravity, but the axis of orientation rotated from the gravity axis in the counterclockwise direction. The data suggest that both gravikinesis and graviorientation of gliding Loxodes are instrumental in perfect neutralization of sedimentation at terrestrial conditions.     

The six genes of the Rubisco small subunit multigene family from Mesembryanthemum crystallinum,a facultative CAM plant

The nucleotide sequences of the entire gene family, comprising six genes, that encodes the Rubisco small subunit (rbcS) multigene family in Mesembryanthemum crystallinum (common ice plant), were determined. Five of the genes are arranged in a tandem array spanning 20 kb, while the sixth gene is not closely linked to this array. The mature small subunit coding regions are highly conserved and encode four distinct polypeptides of equal lengths with up to five amino acid differences distinguishing individual genes. The transit peptide coding regions are more divergent in both amino acid sequence and length, encoding five distinct peptide sequences that range from 55 to 61 amino acids in length. Each of the genes has two introns located at conserved sites within the mature peptide-coding regions. The first introns are diverse in sequence and length ranging from 122 by to 1092 bp. Five of the six second introns are highly conserved in sequence and length. Two genes, rbcS-4 and rbcS-5, are identical at the nucleotide level starting from 121 by upstream of the ATG initiation codon to 9 by downstream of the stop codon including the sequences of both introns, indicating recent gene duplication and/or gene conversion. Functionally important regulatory elements identified in rbcS promoters of other species are absent from the upstream regions of all but one of the ice plant rbcS genes. Relative expression levels were determined for the rbcS genes and indicate that they are differentially expressed in leaves.     

Cyclitol production in transgenic tobacco

High levels of cyclic sugar alcohols (cyclitols) correlate with tolerance to osmotic stress in a number of plant species. A gene encoding a cyclitol biosynthesis enzyme from a halophyte, Mesembryanthemum crystallinum has been introduced into tobacco. The gene, lmt1 , encodes a myo -inositol O -methyl transferase that, in M. crystallinum , catalyzes the first step in the stress-induced accumulation of the cyclitol pinitol. Tobacco transformed with the lmt1 cDNA under the control of the CaMV 35S promoter appeared phenotypically normal and exhibited IMT1 enzyme activity. Transformants accumulated a carbohydrate product not detectable in non-transformed control plants. This product was identified by HPLC and NMR as ononitol (1- d -4- O -methyl myo -inositol). Ononitol was a major carbohydrate constituent in leaf tissue of plants expressing the lmt1 gene, accumulating to up to 25% the level of sucrose in transformant seedlings. The identification of ononitol as the IMT1 product and the specific accumulation of this compound in transformed tobacco support a role for ononitol as a stable intermediate in pinitol biosynthesis and indicate that an epimerization activity lacking in tobacco is responsible for the conversion of ononitol to pinitol in M. crystallinum . The production of ononitol in tobacco indicates that plant carbohydrate metabolism is flexible and can accommodate the synthesis and accumulation of non-endogenous metabolites. The transgenic system described here will serve as a useful model to test the ability of cyclitols such as ononitol to confer tolerance to environmental stress in a normally glycophytic plant.     

FINE STRUCTURAL ALTERATIONS IN CELL PARTICLES DURING CHEMICAL CARCINOGENESIS : III. Selective Action of Hepatic Carcinogens Other than 3'-Methyl-4-Dimethylaminoazobenzene on Different Types of Mitochondrial Swelling. Effect of Stimulated Liver Growth

The previous studies on the correlation between tumor incidence and changes in microsomal and mitochondrial swelling during feeding of 3'-methyl-4-dimethylaminoazobenzene to rats have been extended to other hepatic carcinogens. Administration of 4'-fluoro-4-dimethylaminoazobenzene, 4'-ethyl-2-methyl-4-dimethylaminoazobenzene, 2-acetylam-inofluorene, ethionine, and tannic acid were found to produce drastic alterations of the swelling of rat liver mitochondria. In contrast to these compounds, feeding of the non-carcinogenic azobenzene and 4-diethylaminoazobenzene produced only small changes in swelling. Significant modification in the over-all pattern of the swelling curve was observed when the usual concentration of 3'-methyl-4-dimethylaminoazobenzene was reduced, but not when the riboflavin level in the diet was increased tenfold. Feeding of high levels of this dye to the guinea pig did not affect mitochondrial swelling which is consistent with the resistance of this species to azo-dye carcinogenesis. Hypophysectomy provides protection against the alterations, produced by feeding 3'-methyl-4-dimethylaminoazobenzene, in the characteristics of thyroxine- or mercuric chloride-induced mitochondrial swelling. Studies with citric cycle substrates on mitochondrial swelling suggest block of the glutamate α-keto-glutarate pathway after feeding 3'-methyl-4-dimethylaminoazobenzene for 4 weeks. There is a considerable, but reversible, reduction of certain types of mitochondrial swelling in two situations associated with rapid liver growth: after partial hepatectomy and after intraperitoneal injection of 20-methylcholanthrene. Naphthacene, however, which also stimulates rapid liver growth, does not affect mitochondrial swelling.