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.     

Sulfite inhibition of photochemical activity of intact pea leaves

Sulfite treatment of pea leaf disks in light caused a significant decrease in the relative quantum yield of photosynthetic oxygen evolution and energy storage (ES) as measured by photoacoustic (PA) spectroscopy. The inhibition was concentration dependent and was less in darkness than in light, indicating light-dependent inhibitory site(s) on the photosynthetic electron transport chain. Further, in darksulfite-treated leaves, the energy storage was more affected than the relative quantum yield of oxygen evolution, suggesting that photophosphorylation and/or cyclic electron transport around PS I are sites of sulfite action in darkness. The R_fd values, the ratio of fluorescence decrease (fd) to the steady-state fluorescence (fs), decreased significantly in leaves treated with sulfite in light but were not affected in dark-treated ones, confirming the photoacoustic observations. Similarly, the ratio of variable fluorescence (F_v) to maximum fluorescence (F_m), a measure of PS II photochemical efficiency, was affected by sulfite treatment in light and not changed by treatment in darkness. An attempt was made to explain the mechanism of sulfite action on photosynthetic electron transport in light and in darkness.Abbreviations A_PT amplitude of photothermal signal - A_ox amplitude of oxygen signal - ES energy storage - fd fluorescence decrease - fs steady-state fluorescence - F_m maximum fluorescence - F_v variable fluorescence - PA photoacoustic(s)     

The activation of adenylate cyclase by pituitary adenylate cyclase activating polypeptide (PACAP) via helodermin-preferring VIP receptors in human SUP-T1 lymphoblastic membranes.

Competition binding curves, using [125I-acetyl-His1]PACAP-27 as radioligand and dose-effect curves of adenylate cyclase activation in human SUP-T1 lymphoblastic membranes showed that PACAP-27 and PACAP-38 stimulate the enzyme through a single class of helodermin-preferring VIP receptors with the following order of potency: helodermin = [acetyl-His1]PACAP-27 greater than PACAP-38 greater than PACAP-27 greater than VIP. PACAP (6-27) (Ki 0.5-0.8 microM) and [Des-His1, Asn3]PACAP-27 (Ki 1-2 microM) acted as competitive antagonists. Using a series of 13 PACAP-27 analogues and fragments and three VIP analogues, we identified positions 1, 2, 3, 9 and 13 in PACAP-27 as being of importance for high-affinity binding. Thus, we added further evidence for considering that the present helodermin-preferring VIP receptors, when compared to a majority of VIP receptors and PACAP receptors, exhibit an original specificity pattern.     

Effect of medium and temperature of storage on viability of lactic acid bacteria immobilized in κ-carrageenan-locust bean gum gel beads

Summary The influence of various storage solutions and temperature (4°C and 25°C) on viability ofStreptococcus salivarius subsp.thermophilus andLactobacillusdelbrueckii subsp.bulgaricus entrapped in κ-carrageenan-locust bean gum mixed gel beads was studied. The immobilized strains could be stored at 4°C in all storage solutions studied for at least 14 and 11 days respectively before counts decreased to 10⁵c.f.u./mL, which was considered to be the practical limit for their use as inoculum in a fermentation process. The most effective storage solutions for preserving cell viability at 4°C were NaCl, glycerol and sorbitol solutions forS. thermophilus, and PO₄ buffer and sorbitol solutions forL. bulgaricus. At 25°C,S. thermophilus could be stored for over 14 days in all solutions except glycerol, andL. bulgaricus for 4 days in 10% sorbitol.     

Viability and dissemination of spermatia of Gracilaria verrucosa (Gracilariales,Rhodophyta)

The dissemination and viability of Gracilaria verrucosa spermatia were tested. Crosses were performed among three males and three females from Cape Gris Nez, northern France. Laboratory experiments show that spermatia have a mean fertile life of about five hours. Field studies show that spermatia are dispersed by stream and tidal currents and that fertilization can occur at least 80 m from a population.     

Inhibition by heparin and dextran sulfate of stimulated rat pancreatic adenylate cyclase

Heparin inhibited the adenylate cyclase activity of semipurified rat pancreatic plasma membranes stimulated by hormones and by Gpp(NH)p but not by fluoride or when in the persistently active state. When observed, the inhibition was rapid and sustained. It was of a noncompetitive type and never exceeded 20% for secretin. The inhibition of Gpp(NH)p-stimulated activity was more pronounced (48% inhibition at a heparin concentration of 50 μg/ml). For the C-terminal octapeptide of pancreozymin (CCK-8)-stimulated adenylate cyclase, the inhibition amounted to 93% at 50 μg/ml. This inhibition was competitive at low heparin concentration and of a mixed type above 10 μg/ml. Besides, heparin inhibited (I₅₀ = 6 μg/ml) the binding of peptides of the CCK family to their specific receptors without affecting the apparent K_d value of binding. Taken together, these relatively specific effects of heparin gave evidence in favor of the existence of CCK spare receptors. Dextran sulfate was more potent than heparin as an inhibitor of adenylate cyclase activation while chondroitin-4-sulfate and chondroitin-6-sulfate were ineffective. Dansylated pancreatic plasma membranes exhibited characteristics of adenylate cyclase activation by CCK-8 which were similar to those found for untreated membranes exposed to heparin.     

Genetic instability inDrosophila melanogaster: tandem duplications as monitors of intrastrand exchange

Two tandem duplications of the X chromosome associated with the white eye color locus are described. In heterozygous females both revert to a nonduplicated chromosome without detectable meiotic recombination. Clustering of revertants suggests the reversion event occurs in the germ line prior to meiosis. Similarly in males one duplication also reverts with clustering implying a premeiotic event. Revertant X chromosomes derived from males are either nonduplicated or deleted. Intrastrand exchange can account for some but not all revertants recovered.Dedicated to Professor Bauer on the occasion of his seventy-fifth birthday     

Donor deoxyribonucleic acid length and marker effect in pneumococcal transformation.

The efficiency of transformation of point mutations depends upon base pair mismatches during the recombination process. For low-efficiency markers, the genetic information carried on the donor deoxyribonucleic acid is preferentially lost. To understand this elimination process, we investigated the effect of the size of donor deoxyribonucleic acid on the relative efficiency of low-efficiency point mutations. The deoxyribonucleic acid was shortened either by mechanical shearing or by restriction enzyme treatments. The results indicate that transformation by low-efficiency markers was not affected by shortening the distance between them and the end of the molecule any more than was transformation by the other markers. Moreover, no lethal event could be detected for either cell or chromosomal marker survival. These data do not exclude the double-strand-break hypothesis that was proposed to explain the loss of genetic information for low-efficiency markers, but they offer no support for it.