The physiological basis of seed dormancy in Avena fatua. VIII. Action of malonic acid

Adkins, S. W., Symons, S. J. and Simpson, G. M. 1988. The physiological basis of seed dormancy in Avena fatua . VIII. Action of malonic acid - Physiol. Plant, 72: 477–482.
A low concentration of malonic acid (50 m M ) induced germination in four genetically pure dormant lines of Avena fatua L. Sensitivity to this treatment was poor immediately after harvest but increased markedly during after-ripening, indicating that the mode of action of malonic acid (50 m M ) was similar to that of another organic acid, citric acid. Over the concentration range (10–50 m M ) where malonic acid promoted germination, oxygen uptake was also stimulated, and this was before the first visible signs of germination. At higher concentrations (100–300 m M ) where there was no promotion of germination, malonic acid strongly inhibited oxygen uptake. These results show that malonic acid has a dual effect on oxygen uptake and subsequent germination. Low concentrations (10–50 m M ) act by stimulating the Krebs cycle and germination through an acidification reaction like citric acid, and high concentrations (100–300 m M ) act by inhibiting germination through enzymatic restraint of the Krebs cycle.
The stimulation of both oxygen uptake and germination by three established germination promoters (sodium nitrate, citric acid and ethanol) was inhibited by a high concentration of malonic acid (200 m M ) but unaffected by a low concentration (50 m M ). These results show that oxygen uptake, and hence the activity of the Krebs cycle, are important processes involved in the dormancy breaking mechanism of these three promotors.     

Age and growth of the cold-water scleractinian Solenosmilia variabilis and its reef on SW Pacific seamounts

Little is known about growth rates of deep-water reef-forming corals or the rates at which these reefs accumulate. Such information is critical for determining the resilience of the reefs to anthropogenic impacts such as trawling and climate change. We radiocarbon date live-caught and sub-fossil samples of the bioherm-forming coral Solenosmilia variabilis collected from precisely known depths and locations by means of a remotely operated vehicle on seamounts south of Tasmania, Australia. The growth rate of colonies live-caught between 958 and 1,454 m, which spans most of the depth range of the species locally, ranged from 0.84 to 1.25 mm linear extension yr^?1 and tended to be higher in the deeper-caught material. Analysis of skeletal microstructure suggests annual deposition of growth increments near the growing tips, but not closer to the base, as the skeleton is extended and thickened. Dating of sub-fossil material indicates S. variabilis has been present on Tasmanian seamounts for at least the last 47,000 yrs and a reef accumulation rate of 0.27 mm yr^?1.     

Using Lidar Data to Analyse Sinkhole Characteristics Relevant for Understory Vegetation under Forest Cover—Case Study of a High Karst Area in the Dinaric Mountains

In this article, we investigate the potential for detection and characterization of sinkholes under dense forest cover by using airborne laser scanning data. Laser pulse returns from the ground provide important data for the estimation of digital elevation model (DEM), which can be used for further processing. The main objectives of this study were to map and determine the geomorphometric characteristics of a large number of sinkholes and to investigate the correlations between geomorphology and vegetation in areas with such characteristics. The selected study area has very low anthropogenic influences and is particularly suitable for studying undisturbed karst sinkholes. The information extracted from this study regarding the shapes and depths of sinkholes show significant directionality for both orientation of sinkholes and their distribution over the area. Furthermore, significant differences in vegetation diversity and composition occur inside and outside the sinkholes, which indicates their presence has important ecological impacts.     

Na+-K+-ATPase in frog esophagus mucociliary cell membranes: inhibition by protein kinase C activation

We examined protein kinase C (PKC)-dependentregulation ofNa⁺-K⁺-ATPasein frog mucociliary cells. Activation of PKC by12-O-tetradecanoylphorbol-13-acetate (TPA) or 1,2-dioctanoyl-sn-glycerol(diC8) either in intact cells or isolated membranes resulted in aspecific inhibition ofNa⁺-K⁺-ATPaseactivity by ~25-45%. The inhibitory effects in membranes exhibited time dependence and dose dependence [half-maximalinhibition concentration (IC₅₀) = 0.5 ± 0.1 nM and 2.4 ± 0.2 µM, respectively, for TPA anddiC8] and were not influenced byCa²⁺. Analysis of the ouabaininhibition pattern revealed the presence of twoNa⁺-K⁺-ATPaseisoforms with IC₅₀ values forcardiac glycoside of 2.6 ± 0.8 nM and 409 ± 65 nM,respectively. Most importantly, the isoform possessing a higheraffinity for ouabain was almost completely inhibited by TPA, whereasits counterpart was hardly sensitive to the PKC activator. The resultssuggest that, in frog mucociliary cells, PKC regulatesNa⁺-K⁺-ATPaseand that this action is related to the specificNa⁺-K⁺-ATPaseisoform.

     

TheisfA mutation inhibits mutator activity and processing of UmuD protein inEscherichia coli recA730 strains

Further studies on theisfA mutation responsible for anti-SOS and antimutagenic activities inEscherichia coli are described. We have previously shown that theisfA mutation inhibits mutagenesis and other SOS-dependent phenomena, possibly by interfering with RecA coprotease activity. TheisfA mutation has now been demonstrated also to suppress mutator activity inE. coli recA730 andrecA730 lexA51(Def) strains that constitutively express RecA coprotease activity. We further show that the antimutator activity of theisfA mutation is related to inhibition of RecA coprotease-dependent processing of UmuD. Expression of UmuD' from plasmid pGW2122 efficiently restores UV-induced mutagenesis in therecA730 isfA strain and partially restores its mutator activity. On the other hand, overproduction of UmuD'C proteins from pGW2123 plasmid markedly enhances UV sensitivity with no restoration of mutability.     

Different Mechanisms of β-Adrenoceptor Down-Regulation by Chronic Imipramine and Electroconvulsive Treatment: Possible Role for Protein Kinase C

The aim of this study was to find out how protein kinase C (PKC) is involved in down-regulation of the beta-adrenoceptor in cortical slices of rats subjected to antidepressant treatments. The responses of the cyclic AMP generating system to forskolin, isoproterenol, and noradrenaline were tested in the absence and presence of a PKC activator, 12-O-tetradecanoylphorbol 13-acetate (TPA). The antidepressive treatments applied were chronic administration of imipramine and electroconvulsive shock. The potentiating effect of the phorbol ester on cyclic AMP response to isoproterenol was retained in imipramine-treated animals and even accentuated in rats subjected to electroconvulsive treatment; the TPA effect on noradrenaline-induced cyclic AMP response was blunted in rats receiving imipramine, but augmented in those receiving electroconvulsive treatment. In imipramine-treated rats the beta-down-regulation was still evident in the presence of TPA; after electroconvulsive treatment the phorbol ester-induced potentiation was so high that no significant beta-down-regulation could be observed. No procedure affected the response to forskolin. The beta-down-regulation that develops during chronic imipramine treatment differs from that caused by chronic electroconvulsive treatment; in both cases it is not related to the direct effect on adenylate cyclase.     

Flavonoids enantiomer distribution in different parts of goldenrod (Solidago virgaurea L.), lucerne (Medicago sativa L.) and phacelia (Phacelia tanacetifolia Benth.)

Plant material is a rich source of valuable compounds such as flavanones. Their different forms influence bioavailability and biological activity, causing problems with the selection of plant material for specific purposes. The purpose of this research was to determine selected flavanone (eriodictyol, naringenin, liquiritigenin, and hesperetin) enantiomer contents in free form and bonded to glycosides by an RP‐UHPLC‐ESI‐MS/MS method. Different parts (stems, leaves, and flowers) of goldenrod (Solidago virgaurea L.), lucerne (Medicago sativa L.), and phacelia (Phacelia tanacetifolia Benth.) were used. The highest content of eriodictyol was found in goldenrod flowers (13.1 μg/g), where it occurred mainly as the (S)‐enantiomer, and the greatest proportion of the total amount was bonded to glycosides. The richest source of naringenin was found to be lucerne leaves (4.7 μg/g), where it was mainly bonded to glycosides and with the (S)‐enantiomer as the dominant form. Liquiritigenin was determined only in lucerne, where the flowers contained the highest amount (1.2 μg/g), with the (R)‐enantiomer as dominant aglycone form and the (S)‐enantiomer as the dominant glycosylated form. The highest hesperetin content was determined in phacelia leaves (0.38 μg/g), where it was present in the form of a glycoside and only as the (S)‐enantiomer. A comparison of the different analyte forms occurring in different plant parts was performed for the first time.