Comparative Study of Different Iron Compounds in Inhibition of Sphaerotilus Growth

The effectiveness of iron compounds on growth inhibition of Sphaerotilus species was compared. In this study, two strains of Sphaerotilus were tested with different iron concentrations in a synthetic sewage (S-medium) as formulated by Lackey and Wattie (Sewage Works J. 12:669-684, 1940). For both strains, >80% inhibition of the maximum respiration rate was obtained by the following levels of soluble iron concentrations at pH 6.0: iron citrate, 20 mg/liter as Fe; iron cysteine, 5 mg/liter as Fe; and ferrous sulfate, 10 mg/liter as Fe. At a pH of 6.7 with iron citrate (20 mg/liter as Fe), inhibition of both strains was in excess of 50%. Insoluble iron compounds, such as iron hydroxides and ferrous carbonate, were found to be much less effective than the soluble iron compounds as inhibitors of these two strains. Aged iron hydroxide (500 mg/liter as Fe) produced a 70% inhibition in the maximum respiration rate while fresh iron hydroxide (52 mg/liter as Fe) and ferrous carbonate (500 mg/liter as Fe) produced a 20% inhibition. Chemical analyses of the iron-inhibited Sphaerotilus strains showed a close relationship between the inhibition of the organism's growth and the amount of iron sorbed by the organism.     

Comparative Analysis of Tolerant and Susceptible Citrus Reveals the Role of Methyl Salicylate Signaling in the Response to Huanglongbing

Huanglongbing (HLB), associated with Candidatus Liberibacter asiaticus (Las), is the most devastating disease of citrus worldwide. Tolerance to HLB has been observed in some citrus varieties, but its molecular mechanisms are not well understood. Methyl salicylate (MeSA), involved in salicylic acid (SA) signaling, is a critical mobile signal for plant systematic acquired resistance (SAR). This study compared the response of tolerant sour pomelo (Citrus grandis Osbeck) and susceptible Jincheng orange (Citrus sinensis Osbeck) to Las infection. During 18 months of resistance evaluation, sour pomelo displayed significantly delayed and milder symptoms, and tolerated higher levels of Las growth, compared with Jincheng orange. High levels of MeSA were detected in sour pomelo and MeSA responded positively to Las infection. Little MeSA was found in Jincheng orange regardless of Las infection. Correspondingly, the SA content in sour pomelo was significantly higher than that in Jincheng orange. During Las infection, SA levels decreased significantly in sour pomelo but increased in Jincheng orange. These data indicated that MeSA was correlated with tolerance to HLB in citrus. Gene expression analysis showed that CsSAMT1 and CsSABP2-1, involved in the interconversion of MeSA and SA, were related to MeSA accumulation in sour pomelo, and sour pomelo possesses a strong SAR response. Our study indicates that MeSA-mediated SAR plays an important role in citrus tolerance to HLB. This study provides new insights into HLB tolerance in citrus and useful guidance for improving citrus resistance to HLB by manipulation of MeSA signaling in the future.

     

Role of Indole-3-acetic Acid and Gibberellin in the Control of Internodal Elongation in Avena Stem Segments: Long Term Growth Kinetics

Exogenous application of indoleacetic acid results in a significant suppression of the linear growth that is promoted by exogenous gibberellic acid in Avena stem segments in a fashion similar to that previously noted in Avena leaf base segments (van Overbeek and Dowding, 1961, Fourth International Conference Plant Growth Regulation). Treatment with the auxin transport inhibitors, methyl-2-chloro-9-hydroxyfluorene-(9)-carboxylate (CFM) or 2,3,5-triiodobenzoic acid (TIBA), alone promotes elongation growth of the stem segments over that of control growth. This effect is interpreted as being due to the interference in the transport of native indoleacetic acid by CFM and TIBA, thus removing the inhibitory effect of native indoleacetic acid on gibberellin-promoted growth in the internodal intercalary meristem. This results in a greater promotion of internodal growth by native gibberellins. In the presence of (2-chloroethyl) trimethylammonium chloride (CCC), the growth-promoting effects of CFM and TIBA are decreased, and the antiauxin, PCIB (4-chloro-phenoxyisobutyric acid), has no growth-promoting effects whatsoever. These results indicate that the CFM and TIBA-promoted growth require the continuous presence of gibberellins. They further support the view that native indoleacetic acid acts as a growth suppressor hormone in its regulation of gibberellin-promoted internodal extension in Avena shoots.     

The Auxins IAA and 4-Cl-IAA Differentially Modify Gibberellin Action via Ethylene Response in Developing Pea Fruit

This study explores the unique growth-regulatory roles of two naturally occurring auxins, indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA), and their interactions with gibberellin (GA) during early pea (Pisum sativum L.) fruit development. We have previously shown that 4-Cl-IAA can replace the seed requirement in pea pericarp growth (length and fresh weight), whereas IAA had no effect or was inhibitory. When applied simultaneously, gibberellin (GA₃ or GA₁) and 4-Cl-IAA had a synergistic effect on pericarp growth. In the present study, we found that simultaneous application of IAA and GA₃ to deseeded pericarps inhibited GA₃-stimulated growth. The inhibitory effect of IAA on GA-stimulated growth was mimicked by treatment with ethephon (ethylene releasing agent), and the inhibitory effects of IAA and ethylene on GA-mediated growth were reversed by silver thiosulfate (STS), an ethylene action inhibitor. Although pretreatment with STS could retard senescence of IAA-treated pericarps, STS pretreatment did not lead to IAA-induced pericarp growth. Although 4-Cl-IAA stimulated growth whereas IAA was ineffective, both auxins induced similar levels of ethylene evolution. However, only 4-Cl-IAA-stimulated growth was insensitive to the effects of ethylene. Gibberellin treatment did not influence the amount of ethylene released from pericarps in the presence or absence of either auxin. We propose a growth regulatory role for 4-Cl-IAA through induction of GA biosynthesis and inhibition of ethylene action. Additionally, ethylene (IAA-induced or IAA-independent) may inhibit GA responses under physiological conditions that limit fruit growth.     

Comparative Effects of Substituted Pyrimidines on Growth and Gibberellin Biosynthesis in Gibberella fujikuroi

The fungicide α-(2,4-dichlorophenyl)-α-phenyl-5-pyrimidine methyl alcohol (triarimol) and four other structural analogs of this substance, in which one or more of the substituents were varied, were tested for their comparative effects on growth and gibberellin biosynthesis in the fungus Gibberella fujikuroi. Each of the five analogs tested was capable of inhibiting growth as measured by dry weight in 5-day-old cultures. Three of them [α-(2-chlorophenyl)-α-(4-chlorophenyl)-5-pyrimidine methyl alcohol, fenarimol; α-(2-chlorophenyl)-α-(4-fluorophenyl)-5-pyrimidine methyl alcohol, nuarimol; and triarimol] were effective at appreciably lower concentrations than the other two [α-(4-chlorophenyl)-α-(1-methylethyl)-5-pyrimidine methyl alcohol, experimental compound EL 509; and α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methyl alcohol, ancymidol].     

A Novel System for the Launch of Alphavirus RNA Synthesis Reveals a Role for the Imd Pathway in Arthropod Antiviral Response

Alphaviruses are RNA viruses transmitted between vertebrate hosts by arthropod vectors, primarily mosquitoes. How arthropods counteract alphaviruses or viruses per se is not very well understood. Drosophila melanogaster is a powerful model system for studying innate immunity against bacterial and fungal infections. In this study we report the use of a novel system to analyze replication of Sindbis virus (type species of the alphavirus genus) RNA following expression of a Sindbis virus replicon RNA from the fly genome. We demonstrate deficits in the immune deficiency (Imd) pathway enhance viral replication while mutations in the Toll pathway fail to affect replication. Similar results were observed with intrathoracic injections of whole virus and confirmed in cultured mosquito cells. These findings show that the Imd pathway mediates an antiviral response to Sindbis virus replication. To our knowledge, this is the first demonstration of an antiviral role for the Imd pathway in insects.     

Growth Pattern of Tall and Short Lines of Rice and their Response to Gibberellin

The growth pattern of two types of dwarfness in rice was studied.The difference in height of the tall and short Peta plants wasapparent even at the seedling stage. In the dwarf and in thenormal Century Patna 231 the difference in height was apparentonly after panicle initiation. The four lines had the same numberof elongated internodes, with the taller lines having longerinternodes. The application of gibberellin resulted in increased plant height,longer internodes, blades and leaf sheaths, and decreased tillernumber. Century Patna 231-dwarf showed the least, and shortPeta the greatest, response to gibberellin application.     

Comparative Expression Profiling Reveals an Essential Role for Raldh2 in Epimorphic Regeneration

Zebrafish have the remarkable ability to regenerate body parts including the heart and fins by a process referred to as epimorphic regeneration. Recent studies have illustrated that similar to adult zebrafish, early life stage larvae also possess the ability to regenerate the caudal fin. A comparative microarray analysis was used to determine the degree of conservation in gene expression among the regenerating adult caudal fin, adult heart, and larval fin. Results indicate that these tissues respond to amputation/injury with strikingly similar genomic responses. Comparative analysis revealed raldh2, a rate-limiting enzyme for the synthesis of retinoic acid, as one of the most highly induced genes across the three regeneration platforms. In situ localization and functional studies indicate that raldh2 expression is critical for the formation of wound epithelium and blastema. Patterning during regenerative outgrowth was considered to be the primary function of retinoic acid signaling; however, our results suggest that it is also required for early stages of tissue regeneration. Expression of raldh2 is regulated by Wnt and fibroblast growth factor/ERK signaling.     

Effects of Kinetin, IAA, and Gibberellin on Ethylene Production, and Their Interactions in Growth of Seedlings

Kinetin in concentrations of 10⁻⁸ to 10⁻⁴ m, stimulated ethylene production in 3 and 4-day old etiolated seedlings of Alaska pea (Pisum sativum L. var. Alaska). Seedlings of other species responded similarly. The response to kinetin depended on the age of the seedlings.     

The Role of Ethylene in Growth and Endopolygalacturonase Production by Sclerotium rolfsii

Growth of and endopolygalacturonase production by Sclerotium rolfsii was better on a defined mineral medium than on a medium containing segments of tomato leaf petioles. The effect of treatment with ethylene (10μl/l) upon endopolygalacturonase activity with investigated at various stages of growth, in a mineral defined medium. Addition of ethylene to a 10 days-old culture of S. rolfsii resulted in a decrease in activity by day 14, whereas the addition of ethylene to a 4, 6 and 8 days old cultures resulted in an increase in endopolygalacturonase activity. Ethylene seems to have little or no stimulating effect upon growth of S. rolfsii when applied after 8 days. However, inhibited fungal growth, after the addition of ethylene at earlier stages of growth, was obtained due to the depletion of oxygen from sealed culture flasks. Endopolygalacturonase was extracted and purified from control cultures after 14 days of growth. Fractionation of this enzyme protein on Sephadex G-100 gel filtration columns resulted in two peaks of activity measured by the release of reducing sugars from polygalacturonic acid (PGA).     

Comparative Genomic Analysis Reveals a Critical Role of De Novo Nucleotide Biosynthesis for Saccharomyces cerevisiae Virulence

In recent years, the number of human infection cases produced by the food related species Saccharomyces cerevisiae has increased. Whereas many strains of this species are considered safe, other ‘opportunistic’ strains show a high degree of potential virulence attributes and can cause infections in immunocompromised patients. Here we studied the genetic characteristics of selected opportunistic strains isolated from dietary supplements and also from patients by array comparative genomic hybridization. Our results show increased copy numbers of IMD genes in opportunistic strains, which are implicated in the de novo biosynthesis of the purine nucleotides pathway. The importance of this pathway for virulence of S. cerevisiae was confirmed by infections in immunodeficient murine models using a GUA1 mutant, a key gene of this pathway. We show that exogenous guanine, an end product of this pathway in its triphosphorylated form, increases the survival of yeast strains in ex vivo blood infections. Finally, we show the importance of the DNA damage response that activates dNTP biosynthesis in yeast cells during ex vivo blood infections. We conclude that opportunistic yeasts may use an enhanced de novo biosynthesis of the purine nucleotides pathway to increase survival and favor infections in the host.     

Inhibition of Gibberellin Production in the Fungi Gibberella fujikuroi and Sphaceloma manihoticola by Plant Growth Retardants

The effect of different types of plant growth retardants on fungal gibberellin (GA) formation has been studied in cultures of Gibberella fujikuroi and Sphaceloma manihoticola. Quaternary ammonium compounds (chlormequat chloride, mepiquat chloride, Amo-1618), triazoles (uniconazole and several experimental compounds), and the norbornanodiazetine tetcyclacis inhibited GA biosynthesis in both fungal species. Concentrations between 2 × 10⁻⁴ and 10⁻⁹m were required for a 50% inhibition of the production of gibberellin A₃ in Gibberella fujikuroi and of giberellin A₄ in Sphaceloma manihoticola. The formation of other prominent GAs was affected at a similar degree of intensity. Tetcyclacis was the most active compound in both fungi. Compared to the growth retardants mentioned above, the biological activity of chlorphonium chloride was low. The acylcyclohexanediones prohexadione and LAB 198 999 had virtually no activity. Most likely, this lack of activity is due to a rapid metabolism of the compounds in the cultures. For the triazole-type compounds and tetcyclacis, a relatively distinct correlation exists in their ability to inhibit GA formation in fungal cultures, to block ent-kaurene oxygenase in a cell-free system, and to reduce shoot growth of rice seedlings. Due to differences in their metabolic fate and species specificities, such conclusions cannot be made for the other compounds.     

Growth Inhibition and Recovery in Roots Following Temporary Treatment with Auxin

Continuous recording (streak photography) of elongation of roots treated with IAA (10^–6–10^–7M) showed that removal of IAA from the nutrient solution resulted in a rapid resumption of elongation, unless the IAA treatment was shorter than 60 min. If it was shorter, the recovery was delayed, so that it occurred about 1 hour after the beginning of the treatment, independently of the duration of the treatment, down to 4 min. This behavior of roots was observed in all the species investigated (corn, pea, sunflower, onion), also in response to NAA and 2,4-D. This time lag in recovery of elongation after brief auxin treatment is discussed in connection with the radial concentration gradient of auxin in the root imposed by external auxin. The possible role of a radial gradient of auxin (concentration decreasing with distance from the center) in the control of root elongation is suggested.     

The Role of Ethylene in the Inhibition of Rooting under Low Oxygen Tensions

A 60-fold increase in ethylene content was observed in stem cuttings of chrysanthemum (Chrysanthemum × morifolium Ramat.) held in aero-hydroponics under anoxic conditions during the 8 to 12 days necessary for adventitious root formation. Ethylene, 1-aminocyclopropane-1-carboxylic acid, and 10-(malonylamino) cyclopropane-1-carboxylic acid contents were highest in the immersed portion of the cuttings, but there was substantial ethylene produced by the anoxic, misted portions of the cutting above the liquid. Application of ethylene (10 microliters per liter) to chrysanthemum cuttings stimulated root development in cuttings held in high dissolved oxygen concentrations (8.0 milligrams per liter). Since the application of ethylene did not inhibit rooting in cuttings held at low dissolved oxygen concentrations (2.0 milligrams per liter), the inhibition of rooting under low oxygen concentrations is not mediated by the observed increase in endogenous ethylene content.     

赤霉素信号在非生物胁迫中的作用及其调控机制研究进展

赤霉素(GA)能促进种子萌发和植物生长发育。近年来的研究表明赤霉素这一激素在植物响应非生物胁迫中同样发挥着重要的作用。植物通过调节GA生物合成、信号转导及其生物活性提高胁迫耐受性。综述了赤霉素在应对常见的几类非生物胁迫中所起的作用,分析了其合成、信号转导通路调控机制以及赤霉素与其他激素在响应非生物胁迫的关系。