Pseudomonas syringae pv. syringae B728a hydrolyses indole-3-acetonitrile to the plant hormone indole-3-acetic acid

Nitrilase enzymes catalyse the hydrolysis of nitrile compounds to the corresponding carboxylic acid and ammonia, and have been identified in plants, bacteria and fungi. There is mounting evidence to support a role for nitrilases in plant–microbe interactions, but the activity of these enzymes in plant pathogenic bacteria remains unexplored. The genomes of the plant pathogenic bacteria Pseudomonas syringae pv. syringae B728a and Pseudomonas syringae pv. tomato DC3000 contain nitrilase genes with high similarity to characterized bacterial arylacetonitrilases. In this study, we show that the nitrilase of P. syringae pv. syringae B728a is an arylacetonitrilase, which is capable of hydrolysing indole-3-acetonitrile to the plant hormone indole-3-acetic acid, and allows P. syringae pv. syringae B728a to use indole-3-acetonitrile as a nitrogen source. This enzyme may represent an additional mechanism for indole-3-acetic acid biosynthesis by P. syringae pv. syringae B728a, or may be used to degrade and assimilate aldoximes and nitriles produced during plant secondary metabolism. Nitrilase activity was not detected in P. syringae pv. tomato DC3000, despite the presence of a homologous nitrilase gene. This raises the interesting question of why nitrilase activity has been retained in P. syringae pv. syringae B728a and not in P. syringae pv. tomato DC3000.     

Microsatellite analysis of demographic genetic structure in fragmented populations of the tropical tree Symphonia globulifera

We developed genetic markers for three microsatellite loci in the tropical tree Symphonia globulifera and used them to examine the demographic genetic consequences of forest fragmentation. High levels of genetic variation were revealed in samples of adults, saplings, and seedlings. The more-variable loci exhibited less stability in allelic composition across sites and stages. The number of alleles per hectare (ha) of forest was similar when continuous forest plots were compared to plots from fragmented forest for all three stages. This pattern also held for the number of unique multilocus adult and sapling genotypes, but the number of unique seedling genotypes per ha of fragmented forest greatly exceeded expectations based on continuous forest data, probably due to the concentration of seeds into remnant forest patches by foraging bats. Significant inbreeding and genetic differentiation were most often associated with the fragmented forest and the seedlings. Finally, principal component analysis reaffirmed that a bottleneck, acting in concert with pre-existing genetic structure in the adults, had led to enhanced and rapid divergence in the seedlings following deforestation, a result that is of central interest for landscape management.     

Cell Growth and the Structure and Mechanical Properties of the Wall in Internodal Cells of Nitella opaca: II. MECHANICAL PROPERTIES OF THE WALLS

The internodal cells of Nitella opaca L. have been used in anattempt to assess the part which mechanical properties of thewall may play in the control of cell growth. It is shown thatthe wall is mechanically anisotropic in both its plastic andelastic properties, and evidence is presented which indicatesthat this arises from its anisotropy of structure. The degreeof anisotropy is greater in cells with a high growth-rate thanin those with a low growth-rate. Evidence is presented thatthis variation in properties with growth-rate is due wholly,or in part, to changes in the orientation of the crystallinecomponent, in the relative proportion of wall constituents,and in the condition of active groups of the wall components.The findings are in harmony with the theory that extension growthof the cell wall is due to ‘creep’, i.e. disturbancesof the molecular forces within the wall leading to a slow plasticyielding to turgor pressure.     

Cell Growth and the Structure and Mechanical Properties of the Wall in Internodal Cells of Nitella opaca: I. WALL STRUCTURE AND GROWTH

This is the first of two papers dealing with the relationshipbetween growth and the mechanical properties of the wall ininternodal cells of Nitella opaca L. The submicroscopic structure of the cell wall of this alga,as determined by chemical analysis, X-ray crystallography, polarizingmicroscopy, electron microscopy, swelling measurements, andinfra-red spectrography, is described in detail and the changesduring growth are recorded. It has been found that the wallcontains cellulose in the form of cellulose I (type B). Theconstituent microfibrils are preferentially oriented, usuallyin slow helices with considerable angular dispersion about thecommon direction. They are arranged in discrete layers withpectic substances providing an amorphous matrix between microfibrillar-reinforcedlaminations. It is shown that, as the cell elongates, both thestreaming direction in the cell and the mean microfibrillarorientation in the wall change in such a way as to allow thepossibility of a causal connexion between streaming and microfibrillarorientation in a new wall lamella. The orientation in such alamella is undoubtedly modified by subsequent passive extensionmuch as implied in the multi-net growth hypothesis of Roelofsen.     

Regulation of Sodium and Calcium Channels by Signaling Complexes

Membrane depolarization and intracellular calcium transients generated by activation of voltage-gated sodium and calcium channels are local signals, which initiate physiological processes such as action potential conduction, synaptic transmission, and excitation-contraction coupling. Targeting of effector proteins and regulatory proteins to ion channels is an important mechanism to ensure speed, specificity, and precise regulation of signaling events in response to local stimuli. In this article, we review recent experimental results showing that sodium and calcium channels form local signaling complexes, in which effector proteins, anchoring proteins, and regulatory proteins interact directly with ion channels. The intracellular domains of these channels serve as signaling platforms, mediating their participation in intracellular signaling processes. These protein-protein interactions are important for efficient synaptic transmission and for regulation of ion channels by neurotransmitters and intracellular second messengers. These localized signaling complexes are essential for normal function and regulation of electrical excitability, synaptic transmission, and excitation-contraction coupling.     

Kinetic and Thermodynamic Aspects of Sodium-Coupled Amino Acid Transport by Marine Invertebrates

SYNOPSIS. Marine invertebrates absorb amino acids directly acrosstheir external body surfaces. This absorption process occursvia carrier-mediated transport systems which, recent evidencesuggests, may be sodium-dependent. Steady-state amino acid gradientsare maintained at levels exceeding 10³–10⁶ times thatof the external environment. Examination of the standing gradientsof total free amino acids, Na, and K in seven invertebratessuggests that an Na/amino acid cotransport model, or an Na/K/aminoacid cotransport model can account for amino acid gradientsof this magnitude. However, the Na : amino acid coupling coefficientsmust be 2 or 3 depending on factors such as membrane potentialand the intracellular Na activities. Evidence from studies ofL-alanine transport in the integument of the polychaete Glyceradibranchiata is presented showing that, for this case, the Na: alanine coupling coefficient is 3. It is concluded that themodels presented are plausible and readily testable explanationsfor the observed amino acid gradients in marine invertebrates.     

Immunological similarities between specific chloroplast ribosomal proteins from Chlamydomonas reinhardtii and ribosomal proteins from Escherichia coli

Polyclonal antibodies were elicited against seven of the 33 different proteins of the large subunit of the chloroplast ribosome from Chlamydomonas reinhardtii. Three of these proteins are synthesized in the chloroplast and four are made in the cytoplasm and imported. In western blots, six of the seven antisera are monospecific for their respective large subunit ribosomal proteins, and none of these antisera cross-reacted with any chloroplast small subunit proteins from C. reinhardtii. Antisera to the three chloroplast-synthesized ribosomal proteins cross-reacted with specific Escherichia coli large subunit proteins of comparable charge and molecular weight. Only one of the four antisera to the chloroplast ribosomal proteins synthesized in the cytoplasm cross-reacted with an E. coli large subunit protein. None of the antisera cross-reacted with any E. coli small subunit proteins. On the assumption of a procaryotic, endosymbiotic origin for the chloroplast, those chloroplast ribosomal proteins still synthesized within the organelle appear to have retained more antigenic sites in common with E. coli ribosomal proteins than have those which are now the products of cytoplasmic protein synthesis. Antisera to this cytoplasmically synthesized group of chloroplast ribosomal proteins did not recognize any antigenic sites among C. reinhardtii cytoplasmic ribosomal proteins, suggesting that the genes for the cytoplasmically synthesized chloroplast ribosomal proteins either are not derived from the cytoplasmic ribosomal protein genes or have evolved to a point where no antigenic similarities remain.