Differential effects of concanavalin A and phytohemagglutinin on murine immunity. Suppression and enhancement of humoral immunity.

The abilities of concanavalin A (Con A) and phytohemagglutinin P (PHA) to selectively induce different T-cell activities affecting humoral immunity were evaluated. The mitogens were intravenously injected before, with, or after injection of sheep red blood cells (SRBC) into mice, and the 3 to 6-day plaque-forming cell (PFC) responses were assessed. Mitogenic treatment differentially influenced the resultant in vivo PFC responses to SRBC. The in vivo suppressive effects induced by Con A were shown to be temporary; only the Day 4 PFC response was inhibited. Con A given 3 hr before, with, or after the antigenic challenge enhanced the PFC response. In contrast, PHA given at all intervals inhibited both the 4- and 5-day PFC response. Neither mitogen appeared to affect the kinetics of the in vivo PFC response to SRBC. Both mitogens enhanced in vivo DNA synthesis by the splenic cells, and Con A appeared biphasic in its stimulation. Con A-induced effects on the humoral immune response were short-lived and transient, while PHA induced a longer-lasting effect on humoral immunity.     

Stimulation of indole-3-acetic acid production in Rhizobium by flavonoids

Flavonoids activate nod gene expression in Rhizobium resulting in the synthesis of Nod signals which trigger organogenesis in the host plant. This paper shows that nod-inducers also stimulate the production of the phytohormone IAA (indole-3-acetic acid).     

Perception of the auxin signal at the plasma membrane of tobacco mesophyll protoplasts

Auxin-induced variations of transmembrane potential difference have been shown to be a useful tool for analyzing hormone sensitivity in tobacco protoplasts. Using this technique, we demonstrated that protoplasts derived from wild-type, an auxin-resistant mutant and Agrobacterium-rhizogenes transformed plants differed widely in the sensitivity of their electrical response to naphthalene acetic acid. We have used different antibodies, raised to auxin binding proteins (ABP) from maize coleoptiles, or to the axr1 gene product (ABP1), to test whether changes in auxin sensitivity can be correlated with the presence of tobacco proteins immunologically related to this ABP. Titrations indicated that 0.4 nM anti-ABP IgG inhibited 50% of the auxin-specific response of wild-type protoplasts, whereas 0.04 nM or 4 nM anti-ABP IgG were necessary to inhibit the response of mutant and transformed protoplasts, respectively, to the same extent. On wild-type protoplasts, blocking part of the immunoreactive sites with anti-ABP antibodies resulted in a decrease in auxin sensitivity of the electrical response (0.4 nM anti-ABP IgG inducing a 10–fold decrease), whereas addition of maize ABP increased this auxin sensitivity (1 pM ABP1 raised the sensitivity more than 1000–fold). The results obtained suggest that the auxin sensitivity detected by our assay system correlates with the amount of tobacco proteins immunologically related to the axr¹ gene product from maize. A hypothesis accounting for the presence of these proteins at the external surface of tobacco protoplasts and for the effects of hetero-logous maize ABP on auxin sensitivity is proposed.     

Analysis of methionine enkephalin in human pituitary by multi-dimensional reversed-phase high-performance liquid chromatography, radioreceptor assay, radioimmunoassay, fast atom bombardment mass spectrometry, and mass spectrometry—mass spectrometry

Methionine enkephalin (ME = YGGFM) was measured in five individual human post-mortem pituitaries using four different analytical methods, with the objective of comparing the molecular specificities of the methods. Radioreceptor assay (RRA) used a receptor-rich preparation from brain and [³H]etorphine as radioligand to determine ME-like receptoractivity (ME-LR). Radioimmunoassay (RIA) measured ME-like immunoreactivity (ME-LI). Pituitary samples analyzed by RRA and RIA were purified first with a high-performance liquid chromatography (HPLC) gradient on a polymer analytical column. Fast atom bombardment mass spectrometry (FAB-MS) in two different detection modes quantified ME using the protonated molecular ion MH⁺ of ME at 574 a.m.u. and B/E linked-field selected reaction monitoring (SRM) to monitor the specific unimolecular metastable transition that produced the unique amino acid sequence-determining tetrapeptide fragment ion YGGF⁺ from the MH⁺ precursor ion. Both FAB-MS methods used the deuterated internal standard YGG[²H₅-F]M. Samples analyzed with FAB-MS were purified first with multi-dimensional reversed-phase HPLC. The first dimension was an ODS gradient, and the second dimension was a polymer isocratic elution. The following ME amounts were measured (mean ± standard error of the mean): ME-LR, 7.0 ± 1.9 μg g⁻¹ tissue; ME-LI, 1.8 ± 0.7 μg g⁻¹ tissue; MH⁺, 2.7 ± 0.6 μg g⁻¹ tissue; SRM, 3.0 ± 0.8 μg g⁻¹ tissue. The FAB SRM method provided the highest level of molecular specificity amount these four analytical methods used to measure picomole amounts of endogenous ME in a human pituitary.     

Role of the two-component leader sequence and mature amino acid sequences in extracellular export of endoglucanase EGL from Pseudomonas solanacearum.

The egl gene of Pseudomonas solanacearum encodes a 43-kDa extracellular endoglucanase (mEGL) involved in wilt disease caused by this phytopathogen. Egl is initially translated with a 45-residue, two-part leader sequence. The first 19 residues are apparently removed by signal peptidase II during export of Egl across the inner membrane (IM); the remaining residues of the leader sequence (modified with palmitate) are removed during export across the outer membrane (OM). Localization of Egl-PhoA fusion proteins showed that the first 26 residues of the Egl leader sequence are required and sufficient to direct lipid modification, processing, and export of Egl or PhoA across the IM but not the OM. Fusions of the complete 45-residue leader sequence or of the leader and increasing portions of mEgl sequences to PhoA did not cause its export across the OM. In-frame deletion of portions of mEGL-coding sequences blocked export of the truncated polypeptides across the OM without affecting export across the IM. These results indicate that the first part of the leader sequence functions independently to direct export of Egl across the IM while the second part and sequences and structures in mEGL are involved in export across the OM. Computer analysis of the mEgl amino acid sequence obtained from its nucleotide sequence identified a region of mEGL similar in amino acid sequence to regions in other prokaryotic endoglucanases.     

Techniques in plant molecular biology--progress and problems

Progress in plant molecular biology has been dependent on efficient methods of introducing foreign DNA into plant cells. Gene transfer into plant cells can be achieved by either direct uptake of DNA or the natural process of gene transfer carried out by the soil bacterium Agrobacterium. Versatile gene-transfer vectors have been developed for use with Agrobacterium and more recently vectors based on the genomes of plant viruses have become available. Using this technology the expression of foreign DNA, the functional analysis of plant DNA sequences, the investigation of the mechanism of viral DNA replication and cell to cell spread, as well as the study of transposition, can be carried out. In addition, the versatility of the gene-transfer vectors is such that they may be used to isolate genes not amenable to isolation using conventional protocols. This review concentrates on these aspects of plant molecular biology and discusses the limitations of the experimental systems that are currently available.     

Broad-host-range cloning vectors derived from the W-plasmid Sa

Four nonconjugative broad-host-range cloning vectors were derived from the W-plasmid Sa. They are small (M_r 5.6?7.2 × 10⁶), carry several drug-resistance markers, and allow constructing and screening for recombinant plasmids generated by the restriction enzymes EcoRI, PstI, BglII, HindIII, BamHI and SalI,