Induction of cysteine and serine proteases during xylogenesis in Zinnia elegans

The terminal process of xylogenesis, autolysis, is essential for the formation of a tubular system for conduction of water and solutes throughout the whole plant. Several hydrolase types are implicated in autolysis responsible for the breakdown of cytoplasm. Here, we characterize p48h-17 cDNA from in vitro tracheary elements (TEs) of Zinnia elegans which encodes a preproprotein similar to papain. The putative mature protein, a cysteine protease, has a molecular mass of 22,699 Da with a pI of 5.7. DNA gel blot analysis indicated that p48h-17 is likely encoded by one or two genes. The p48h-17 mRNA accumulated markedly in in vitro differentiating TEs, whereas it appeared not to be induced in response to senescence and wounding in the leaves or H₂O₂ challenge in the cultured mesophyll cells. In stems, the expression of the p48h-17 gene was preferentially associated with differentiating xylem. Activity gel assays demonstrated that a cysteine and a serine protease, which had apparent molecular masses of 20 kDa and 60 kDa, respectively, were markedly induced during in vitro TE differentiation. The cysteine protease activity was also preferentially present in the xylem of Zinnia stems. Transient expression of the p48h-17 cDNA in tobacco protoplasts resulted in the production of a 20 kDa cysteine protease. Taken together, the results indicate that the p48h-17 gene appears to be preferentially associated with xylogenesis, and both the cysteine and serine proteases might be involved in autolysis during xylogenesis.     

Presence of unique repeated insertion sequences in nodulation genes of Rhizobium ‘hedysari’

Cloning and sequencing of DNA from a symbiotic large plasmid in Rhizobium hedysari strain IS 123 required for its nodulation of the mediterranean legume crop Hedysarum coronarium (sulla) and complementation studies of nod^- mutant derivatives led to the characterization of a 30-kb region containing common and host-specific nod genes. This DNA region also contained at least six copies of a novel insertion sequence-like structure, some of which appeared to have suffered deletions. This 0.8 kb novel element carries two 17-bp flanking inverted repeats and an open reading frame showing homology with a transposase from Staphylococcus aureus. Hybridization studies revealed that several strains of Rhizobium hedysari carry this element in various copy number. The six copies in strain IS 123 appear clustered specifically within the pSym nod region.The significance of this IS element in rhizobia and its possible use as a probe for taxonomic and phylogenetic studies of Rhizobiaceae is addressed.     

Measurement and modelling of photosynthetic response of pearl millet to soil phosphorus addition

There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the major constraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg^–1 soil, leaf P content increased from 0.65 to 7.0 g kg^–1. Both A and DM had maximal values near 51.7 mg P kg^–1 soil, which corresponded to a leaf P content of 3.2 g kg^–1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (g_s) tripled, and mean leaf internal CO₂ concentration ([CO₂]_i) decreased from 260 to 92 L L^–1, thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both K_M, which is mathematically equivalent to quantum efficiency, and V_max, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg^–1, with peak values between 4 and 5 g P kg^–1. Polynomial equations relating K_M and V_max, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny.     

The mechanical significance of the occlusal geometry of great ape molars in food breakdown

Analyses of dental function are an essential component of the study of human evolution. However, with few exceptions, they have utilized the traditional analogizing method of comparative anatomy, and have assumed rather than demonstrated that proposed adaptive characters confer a performance benefit. Since food reduction is a mechanical process, it is appropriate to measure performance using mechanical parameters, specifically the ability of a given morphology to induce failure in food particle by either of the two major regimes: crush and shear, corresponding to simple stresses (tensile and compressive) and shear stress, respectively. We apply finite elements stress analysis to model the relationship between the angulation of the intercuspal occlusal surfaces in a “puncture crushing” mode of mastication. On the basis of morphological data acquired from sectioned great ape molars, we have predicted the nature, magnitude and distribution of stress in a standard food particle by models representing each morphotype. Results indicate that the blunt-cusped molars ofHomo, the gradually-sloping supporting (buccal) cusps but high-angled guiding (lingual) cusps of the lower molars ofPan, and the high angled occlusal surfaces ofGorillaare all more likely to fracture small food particles by shear, while the gradually sloping occlusal surfaces ofPongomolars are more likely to break them down by “crush”. Mechanisms of food failure induced by molars ofPanandHomowill vary according to the orientation of the tooth–food contacting surfaces, which in turn will vary according to the size of the food particle. These genera may be able to break food down either by shear or by “crush”.     

FT Ⅰ, a novel positive myeloid-lineage-specific transcription regulatory element within the mouse myeloperoxidase gene enhancer, En 1

INTanDUCTI0NMyeloidcelldifferentiati0n,inwhichmultip0tentialprogenitorcellsarec0nvertedint00neofthesixmaturedifferentiatedcells,i.e.,erythr0cytes,platelets(megakary-ocytes),macr0phages,neutr0phils,e0sinophilsandbas0phils,involvestemporalre-gulati0nofexpression0fanumberoflineage-anddifferentiationstage-specificgenes.Understandingthedevel0pmentalspecificationoflineageaJswellasmaturationstageassociatedpatterns0fgeneexpressioninmyel0idcelldifferentiationrequiresanin-sightintothecontrol0findivid…     

Molecular modelling of theDolichos biflorus seed lectin and its specific interactions with carbohydrates: α-D-N-acetyl-galactosamine,Forssman disaccharide and blood group A trisaccharide

The three-dimensional structure ofDolichos biflorus seed lectin has been constructed using five legume lectins for which high resolution crystal structures were available. The validity of the resulting model has been thoroughly investigated. Final structure optimization was conducted for the lectin complexed with GalNAc, providing thereby the first three-dimensional structure of lectin/GalNAc complex. The role of theN-acetyl group was clearly evidenced by the occurrence of a strong hydrogen bond between the protein and the carbonyl oxygen of the carbohydrate and by hydrophobic interaction between the methyl group and aromatic amino acids. Since the lectin specificity is maximum for the Forssman disaccharide GalNAc(1–3)GalNAc-O-Me and the blood group A trisaccharide GalNAc(1–3)[Fuc(1–2)]Gal-O-Me, the complexes with these oligosaccharides have been also modelled.     

A cell-based reporter assay for the identification of protein kinase C activators and inhibitors

Transmission of extra cellular signals across biological membranes results in the generation of lipid metabolites which in turn influence specific cellular events such as cell growth or differentiation. Many of these lipid messengers can activate protein kinase C (PKC) isozymes of which one function is to perpetuate the extracellular signals to the nucleus by phosphorylating other targets proteins. We have engineered mammalian cell lines to identify and evaluate activators and inhibitors of PKC-dependent and independent signal transduction pathways. The A31 mouse fibroblast cell line, has been stably transfected with a construct containing a triplet repeat of the TPA response element (TRE) upstream of a thymidine kinase promoter fused to the human growth hormone (hGH) gene. A31 cells containing this reporter construct exhibit significant increases in hGH secretion following stimulation by phorbol esters or other mitogens. The levels of hGH secretion are modulated in this system using different pharmacological agents. We demonstrate that this assay can be used to identify specific and general inhibitors as well as activators of the signal transduction pathway mediated by PKC isozymes. (Mol Cell Biochem141: 129–134, 1994)