Water relations, gas exchange and abscisic acid content of Lupinus cosentinii leaves in response to drying different proportions of the root system

Soil columns in which the root system was divided into threeequal layers, each 24 cm in diameter and 33 cm high were usedto examine the influence of drying different proportions ofthe root system on the water relations, gas exchange and abscisicacid (ABA) concentration of lupin (Lupinus cosentinii Guss.cv. Eregulla) leaves. The treatments imposed were (i) all threelayers adequately watered (control), (ii) the upper layer unwateredwith the remaining layers kept adequately watered, (iii) thetwo upper layers unwatered with the basal layer kept adequatelywatered, (iv) all three layers unwatered. The treatments wereapplied at 56 d after sowing (DAS), and continued for 21 d inthe treatment in which the three layers were dried and for 36d in the other three treatments. After 21 d, the soil matricpotential in the layers that were unwatered had decreased toemdash 1.3MPa, compared to - 0.03 MPa in the adequately-wateredlayers. Within 8 d of cessation of watering, plants with the entireroot system in drying soil had significantly lower stomatalconductances, lower rates of net photosynthesis, and higherleaf ABA contents than did adequately-watered plants. Whilethe leaf osmotic potential decreased within 8 d of cessationof watering, the leaf water potential did not change for thefirst 15 d after water was withheld. After withholding waterfrom all layers, the shoot dry matter was 63% lower than thatin the adequately-watered plants. In the two partially-droughtedtreatments, 17% and 48% of the root length was subjected todrying. Compared to the adequately-watered plants, drying upto 50% of the root system for 36 d, in the two partially-droughtedtreatments, did not reduce stomatal conductance, net photosynthesis,or plant growth. Similarly, there was no significant effecton leaf water potential or osmotic potential. When either theupper or upper and middle layers of soil were dried, the ABAcontent of the leaves for most of the drying period was slightly,but not significantly, higher than in leaves of the adequately-wateredplants. The results suggest that lupins with a well-established rootsystem can utilize localized supplies of available soil waterto maintain leaf gas exchange despite appreciable portions ofthe root system being in dry soil. In contrast to other studies,the results also suggest that when only a portion of the soilvolume is dry and adequate water is available in the wet zone,root signals do not influence stomatal conductance and leafgas exchange of lupin. Key words: Abscisic acid, gas exchange, lupins, split-roots, water deficit     

Microcalorimetric investigations of the interactions of small ions with arterial elastin

The enthalpies of interactions of porcine arterial elastin with alkali metal and alkali earth halides and sulphates were investigated by means of flow microcalorimetry and the stoichiometry measured using radiotracer techniques. In aqueous solutions, all alkali earth halides interacted exothermically at concentrations ranging from 0.01 to 2.5M. All the alkali metal halides, particularly NaCl, exhibited complex concentration-dependent interactions, exothermic at low concentrations and endothermic at high concentrations. Both the anion and cation contributed to the response, although the anion seemed to dominate. SO interacted most strongly of the anions tested. All interactions were reversible in the sense that repeat experiments gave identical results, but the enthalpy of “adsorption” was generally different from that of “desorption.” The enthalpy of interaction depended on the conformation of the elastin in a salt-specific manner. For example, CaCl₂ and MgCl₂ interacted similarly in water but very differently in 1 : 1 water : methanol. © 1994 John Wiley & Sons, Inc.     

Theoretical conformational analysis of the opioid δ antagonist H-Tyr-Tic-Phe-OH and the μ agonist H-Tyr-D-Tic-Phe-NH2

A molecular mechanics study (grid search and energy minimization) of the highly δ receptor-selective δ opioid antagonist H-Tyr-Tic-Phe-OH (TIP; Tic: tetrahydroisoquinoline-3-car-boxylic acid) resulted in four low energy conformers with energies within 2 kcal/mol of that of the lowest energy structure. These four conformers contain trans peptide bonds only and represent compact structures showing various patterns of aromatic ring stacking. The centrally located Tic residue imposes several conformational constraints on the N-terminal dipeptide segment; however, the results of molecular dynamics simulations indicated that this tripeptide still shows some structural flexibility, particularly at the Phe³ residue. Analogous studies performed with the structurally related μ receptor-selective μ agonist H-Tyr-D -Tic-Phe-NH₂ resulted in low energy structures that were also compact but showed patterns of ring stacking different from those obtained with TIP. Superim-position of low energy conformers of TIP and H-Tyr-D -Tic-Phe-NH₂ revealed that the Phe³ residues of the L -Tic- and the D -Tic peptide were always located on opposite sides of the plane defined by the Tic residue, thus providing an explanation for the distinct activity profiles of the two compounds in structural terms. Attempts to demonstrate spatial overlap between the pharmacophoric moieties of low energy conformers of TIP and the nonpeptide δ antagonist naltrindole were made by superimposing either the Tyr¹ and Tic² aromatic rings and the N-terminal amino group or the Tyr¹ and Phe³ aromatic rings and the N-terminal amino group of the peptide with the corresponding aromatic rings and nitrogen atom in the alkaloid structure. In each case a low energy structure of TIP was found that showed good spatial overlap of all three specified pharmacophoric groups. These two conformers may represent candidate structures for the δ receptor-bound conformation of TIP. © 1994 John Wiley & Sons, Inc.     

IMMUNOLOCALIZATION OF CENTRIN IN OXYRRHIS MARINA (DINOPHYCEAE)1

A new polyclonal antibody was raised against centrin isolated from the flagellate green alga Spermatozopsis similis (Chlorophyta; anti-SSC). It stains by immunofluorescence and immunoelectron microscopy well-known reference systems for centrin like the nucleus–basal body connectors in Chlamydomonas reinhardtii (Chlorophyta) and the system II fibers (rhizoplasts) of Scherffelia dubia (Chlorophyta). In addition, it recognizes in immunoblots a single 20-kDa protein in isolated cytoskeletons of Spermatozopsis similis and Tetraselmis striata (Chlorophyta) as well as purified centrin isolated from Tetraselmis striata. Using this antibody, centrin was localized in whole cells and isolated cytoskeletons of Oxyrrhis marina Dujardin (Dinophyceae) by immunofluorescence and immunogold electron microscopy. In the flagellar apparatus of O. marina, five different structures were antigenic. Four short fibers (connectives 1–4) link the basal bodies to the four major fibrous flagellar roots, which do not cross-react with anti-centrin. The most prominent of the labeled structures (connective 5), a crescent-shaped fiber, extends from the flagellar canal of the transverse flagellum along the base of the tentacle to the flagellar canal of the longitudinal flagellum, interconnecting the distal parts of the microtubular roots/bands in the basal apparatus. For most of its length, it underlies and is connected to a transversely oriented subamphiesmal microtubular band. In immunoblot analyses, anti-SSC recognizes only a single 20-kDa protein in cytoskeletons of O. marina. Functional and phylogenetic aspects of centrin-containing structures in dinoflagellates are discussed.     

Changes in Metabotropic Glutamate Receptor mRNA Levels Following Global Ischemia: Increase of a Putative Presynaptic Subtype (mGluR4) in Highly Vulnerable Rat Brain Areas

Abstract: Metabotropic glutamate receptors mediate their intracellular response by coupling to G proteins and may be divided into three subfamilies: mGluR1 and mGluR5, which stimulate phosphatidylinositol hydrolysis; mGluR2 and mGluR3, which are negatively coupled to cyclic AMP formation; and mGluR4 and mGluR6, which also inhibit forskolin-stimulated cyclic AMP formation. The mGluR4 subtypes may represent l -2-amino-4-phosphonobutyrate-sensitive presynaptic autoreceptors, and two alternatively spliced variants of the mGluR4 coding for two receptors with different C termini have been identified. Using in situ hybridization, we measured the levels of mGluR1–mGluR5 mRNA in regions of the rat brain 24 h after transient global ischemia, a time point when no neuronal damage can yet be observed morphologically. In the hippocampus, the mRNA levels for mGluR1, mGluR2, and mGluR5 were decreased, mGluR3 mRNA levels were unchanged, and the mGluR4 mRNA levels were strongly increased. The strongest increase appeared to be in the mRNA encoding mGluR4b. The mGluR4 mRNA was also increased in the parietal cortex, whereas the ventral posteromedial thalamic nucleus showed a small decrease in its mRNA content. These results suggest that vulnerable neurons react to an increased extracellular glutamate concentration by differential regulation of the mRNA for pre- and postsynaptically located metabotropic glutamate receptors.     

Modulation of Adenylylcyclase by Protein Kinase C in Human Neurotumor SK-N-MC Cells: Evidence that the α Isozyme Mediates Both Potentiation and Desensitization

Abstract: Exposure of human SK-N-MC neurotumor cells to 4β-phorbol 12-myristate 13-acetate (PMA) increased isoproterenol stimulation of cyclic AMP levels by severalfold. This potentiation was blocked by inhibitors of protein kinase C (PKC) and did not occur in cells in which PKC had been down-regulated. PMA treatment also enhanced the stimulation by dopamine, cholera toxin, and forskolin. Thus, the effect of PMA on the adenylylcyclase system was postreceptor and involved either the guanine nucleotide binding regulatory (G) proteins or the cyclase itself. As PMA treatment did not impair the inhibition of isoproterenol stimulation by neuropeptide Y, an involvement of the inhibitory G protein G_i was unlikely. Cholate extracts of membranes from control and PMA-treated cells were equally effective in the reconstitution of adenylylcyclase activity in S49 cyc^? membranes, which lack the stimulatory G protein subunit G_sα; thus, G_s did not appear to be the target of PMA action. Membranes from PMA-treated cells exhibited increased adenylylcyclase activity to all stimulators including Mn²⁺ and Mn²⁺ plus forskolin. In addition, activity was increased when control membranes were incubated with ATP and purified PKC from rat brain. This is consistent with a direct effect of PKC on the adenylylcyclase catalyst in SK-N-MC cells. PMA treatment also resulted in a shift to less sensitivity in the K_act for isoproterenol but not for dopamine or CGP-12177 (a β₃-adrenergic agonist) stimulation. Thus, the β₁ but not the D₁ or β₃ receptors were being desensitized by PKC activation. Analysis of SK-N-MC cells by western blotting with antibodies against different PKC isozymes revealed that both the α and ζ isozymes were present in these cells. Whereas PKC-α was activated and translocated from cytosol to membrane by phorbol esters, the ζ isozyme was not. Thus, PKC-α, which has been implicated in desensitization in other cell lines, also appears to potentiate adenylylcyclase activity.     

A synopsis of medullosan pollen organs from the middle Pennsylvanian Mazon creek flora of northeastern Illinois, USA

Six kinds of medullosan pollen organs containing Monoletes-type pollen (prepollen) are described from the middle Pennsylvanian Mazon Creek flora of northeastern Illinois, USA. Codonotheca caduca Sellards and Schopfitheca boulayoides Delevoryas are redescribed and emended diagnoses and new reconstructions are provided. Three forms of Dolerotheca-type pollen organs are described for the first time, along with ultrastructural details of in situ pollen. A sixth kind of pollen organ, tentatively associated with the ovule Stephanospermum konopeonus (Langford) Drinnan, Schramke and Crane, is too poorly preserved for generic assignment but has pollen different from that of other Mazon Creek medullosan pollen organs. This new information on Mazon Creek plants provides important evidence on the diversity of medullosan “pteridosperms” in the flora. Characterization of in situ pollen provides a basis for continuing attempts to associate pollen organs with the variety of co-occuring dispersed ovules.