Phytohormonal effects on rhizosphere processes of maize (Zea mays L.) under phosphorus deficiency

Effects of the hormones indole-3-acetic acid (IAA), gibberellic acid (GA3), and trans-zeatin (t-Z) on growth, P status and rhizosphere processes of maize (Zea mays L., cv. 'Bezemara') were investigated in a pot experiment at two levels of phosphorus availability (+P: water soluble phosphate and -P: sparingly soluble tricalcium phosphate). Six weeks after seed germination, plants were harvested and analysed for dry weight, shoot length, root surface, P concentration, acid phosphatases activity (acid Pase) in shoot and rhizosphere and the content of carboxylic acids and sugars in the rhizosphere. ANOVA was used to estimate the effects of treatments on measured parameters. Hormone application via rhizosphere had a highly significant effect on the growth of whole plants, their P status and rhizosphere processes. GA3 and t-Z promoted quantitatively shoot and root growth and morphological changes, whereas IAA affected the chemical composition of the rhizosphere. In several parameters, the effects of hormone treatment depended on the P status of plants indicating different sensitivity of +P and -P plants to plant growth regulator (PGR) application (significant interaction of hormone application × P availability). The findings help to improve our knowledge, why PGR treatments and plant growth promoting rhizo-microorganisms have varying effects on plants depending on growth conditions

Root exudation of phloridzin by apple seedlings (Malus x domestica Borkh.) with symptoms of apple replant disease

This study investigates the occurrence of the flavonoid phloridzin (phloretin-2'-O-β-D-glucoside) in root exudates of apple seedlings showing growth reduction related to apple replant disease (ARD). The disease is most likely caused by a complex of soil-borne fungi and bacteria, but the etiology remains to be elucidated. Information on specific exudation processes in the rhizosphere of apple seedlings could contribute to our understanding of the conditions triggering ARD development.To procure ARD symptoms, apple seedlings (Malus x domestica Borkh.) were grown in ARD-conductive soil. Root exudates were collected by submerging the roots in a solution of 0.05 mM CaCl2 for a period of 4 h. The fraction of phenolic root exudates was analyzed using HPLC/DAD (high performance liquid chromatography/diode array detector).Results suggest that (i) phloridzin is a constant root exudate of apple seedlings. It was the most abundant phenol in the collected exudates from replant-diseased as well as healthy seedlings. (ii) Phloridzin exudation, related to root dry matter, was the most intensive at the onset of ARD symptom development and lower during the period when symptoms were most severe or outgrown. (iii) In comparison to healthy seedlings, the phloridzin exudation of apple replantdiseased seedlings was significantly higher only at the onset of ARD symptom development, suggesting a response of the plants to infection.The finding of phloridzin in the root exudates of Malus x domestica Borkh. might have consequences for research on the etiology of ARD. Specialized pathogenic microorganisms could be attracted by this distinct compound. Since it is very characteristic of apple plants, phloridzin might be the compound that ARD-causing microorganisms utilize to recognize their host. For practical applications, phloridzin root exudation could therefore be a parameter in evaluating ARD-susceptibility of different rootstocks

Protein Phosphatase 1 Dephosphorylates Profilin-1 at Ser-137

Profilin-1 (PFN1) plays an important role in the control of actin dynamics, and could represent an important therapeutic target in several diseases. We previously identified PFN1 as a huntingtin aggregation inhibitor, and others have implicated it as a tumor-suppressor. Rho-associated kinase (ROCK) directly phosphorylates PFN1 at Ser-137 to prevent its binding to polyproline sequences. This negatively regulates its anti-aggregation activity. However, the phosphatase that dephosphorylates PFN1 at Ser-137, and thus activates it, is unknown. Using a phospho-specific antibody against Ser-137 of PFN1, we characterized PFN1 dephosphorylation in cultured cells based on immunocytochemistry and a quantitative plate reader-based assay. Both okadaic acid and endothall increased pS137-PFN1 levels at concentrations more consistent with their known IC50s for protein phosphatase 1 (PP1) than protein phosphatase 2A (PP2A). Knockdown of the catalytic subunit of PP1 (PP1Cα), but not PP2A (PP2ACα), increased pS137-PFN1 levels. PP1Cα binds PFN1 in cultured cells, and this interaction was increased by a phosphomimetic mutation of PFN1 at Ser-137 (S137D). Together, these data define PP1 as the principal phosphatase for Ser-137 of PFN1, and provide mechanistic insights into PFN1 regulation by phosphorylation

Functional Phenotypic Rescue of Caenorhabditis elegans Neuroligin-Deficient Mutants by the Human and Rat NLGN1 Genes

Neuroligins are cell adhesion proteins that interact with neurexins at the synapse. This interaction may contribute to differentiation, plasticity and specificity of synapses. In humans, single mutations in neuroligin encoding genes lead to autism spectrum disorder and/or mental retardation. Caenorhabditis elegans mutants deficient in nlg-1, an orthologue of human neuroligin genes, have defects in different behaviors. Here we show that the expression of human NLGN1 or rat Nlgn1 cDNAs in C. elegans nlg-1 mutants rescues the fructose osmotic strength avoidance and gentle touch response phenotypes. Two specific point mutations in NLGN3 and NLGN4 genes, involved in autistic spectrum disorder, were further characterized in this experimental system. The R451C allele described in NLGN3, was analyzed with both human NLGN1 (R453C) and worm NLG-1 (R437C) proteins, and both were not functional in rescuing the osmotic avoidance behavior and the gentle touch response phenotype. The D396X allele described in NLGN4, which produces a truncated protein, was studied with human NLGN1 (D432X) and they did not rescue any of the behavioral phenotypes analyzed. In addition, RNAi feeding experiments measuring gentle touch response in wild type strain and worms expressing SID-1 in neurons (which increases the response to dsRNA), both fed with bacteria expressing dsRNA for nlg-1, provided evidence for a postsynaptic in vivo function of neuroligins both in muscle cells and neurons, equivalent to that proposed in mammals. This finding was further confirmed generating transgenic nlg-1 deficient mutants expressing NLG-1 under pan-neuronal (nrx-1) or pan-muscular (myo-3) specific promoters. All these results suggest that the nematode could be used as an in vivo model for studying particular synaptic mechanisms with proteins orthologues of humans involved in pervasive developmental disorders

Untersuchungen ueber die hormonelle Steuerung des Blatt/Ruebenkoerper-Verhaeltnisses bei Zuckerrueben (Beta vulgaris L. sep. vulgaris var. altissima [Doell]) unter besonderer Beruecksichtigung der Abscisinsaeure

Junge Blaetter besitzen einen hoeheren ABA-Gehalt als voll entwickelte; das Verhaeltnis hydrolysierbare Konjugate (ABA K)/freie ABA betraegt ca. 2. Trockenstress bewirkt einen signifikanten Anstieg des freien Hormons und der ABA K. Voll entwickelte Blaetter reagieren auf Wassermangel mit einem staerkeren Gehaltsanstieg. Eine Depotfunktion der ABA K konnte nur nach starker Stresseinwirkung an abgeschnittenen Blaettern beobachtet werden, nicht in intakten Pflanzen. Trockenstress induziert neben einer Veraenderung des Hormonhaushaltes auch eine Verschiebung des Blatt/Ruebenkoerper-Verhaeltnisses. Zwischen der Anreicherung von ABA und dem Organverhaeltnis besteht eine nichtlineare Beziehung. Niedrige ABA-Gehalte korrelieren mit einigen hohen Blatt- und einem relativ niedrigen Ruebenkoerperertrag. Es laesst sich unter den jeweiligen Anzuchtbedingungen ein ABA-Gehalt ermitteln, bei dem der Ruebenkoerperertrag maximal ist. Hoehere ABA-Gehalte sind von Ertragsdepressionen begleitet. Die Behandlung mit einem Pseudoauxinpraeparat (2,4-D) erhoeht den ABA-Gehalt und damit gleichzeitig den Ruebenkoerperanteil der Pflanze. Dies legt eine kausale Beziehung zwischen ABA-Anreicherung und dem Organverhaeltnis nahe. Es besteht allerdings kein monokausaler ZusammenhangSIGLEAvailable from: Halle Univ. (Germany). Universitaetsbibliothek / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Mover Is a Homomeric Phospho-Protein Present on Synaptic Vesicles

With remarkably few exceptions, the molecules mediating synaptic vesicle exocytosis at active zones are structurally and functionally conserved between vertebrates and invertebrates. Mover was found in a yeast-2-hybrid assay using the vertebrate-specific active zone scaffolding protein bassoon as a bait. Peptides of Mover have been reported in proteomics screens for self-interacting proteins, phosphorylated proteins, and synaptic vesicle proteins, respectively. Here, we tested the predictions arising from these screens. Using flotation assays, carbonate stripping of peripheral membrane proteins, mass spectrometry, immunogold labelling of purified synaptic vesicles, and immuno-organelle isolation, we found that Mover is indeed a peripheral synaptic vesicle membrane protein. In addition, by generating an antibody against phosphorylated Mover and Western blot analysis of fractionated rat brain, we found that Mover is a bona fide phospho-protein. The localization of Mover to synaptic vesicles is phosphorylation dependent; treatment with a phosphatase caused Mover to dissociate from synaptic vesicles. A yeast-2-hybrid screen, co-immunoprecipitation and cell-based optical assays of homomerization revealed that Mover undergoes homophilic interaction, and regions within both the N- and C- terminus of the protein are required for this interaction. Deleting a region required for homomeric interaction abolished presynaptic targeting of recombinant Mover in cultured neurons. Together, these data prove that Mover is associated with synaptic vesicles, and implicate phosphorylation and multimerization in targeting of Mover to synaptic vesicles and presynaptic sites.peerReviewe