Enhanced Lignin Monomer Production Caused by Cinnamic Acid and Its Hydroxylated Derivatives Inhibits Soybean Root Growth

Cinnamic acid and its hydroxylated derivatives (p-coumaric, caffeic, ferulic and sinapic acids) are known allelochemicals that affect the seed germination and root growth of many plant species. Recent studies have indicated that the reduction of root growth by these allelochemicals is associated with premature cell wall lignification. We hypothesized that an influx of these compounds into the phenylpropanoid pathway increases the lignin monomer content and reduces the root growth. To confirm this hypothesis, we evaluated the effects of cinnamic, p-coumaric, caffeic, ferulic and sinapic acids on soybean root growth, lignin and the composition of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) monomers. To this end, three-day-old seedlings were cultivated in nutrient solution with or without allelochemical (or selective enzymatic inhibitors of the phenylpropanoid pathway) in a growth chamber for 24 h. In general, the results showed that 1) cinnamic, p-coumaric, caffeic and ferulic acids reduced root growth and increased lignin content; 2) cinnamic and p-coumaric acids increased p-hydroxyphenyl (H) monomer content, whereas p-coumaric, caffeic and ferulic acids increased guaiacyl (G) content, and sinapic acid increased sinapyl (S) content; 3) when applied in conjunction with piperonylic acid (PIP, an inhibitor of the cinnamate 4-hydroxylase, C4H), cinnamic acid reduced H, G and S contents; and 4) when applied in conjunction with 3,4-(methylenedioxy)cinnamic acid (MDCA, an inhibitor of the 4-coumarate:CoA ligase, 4CL), p-coumaric acid reduced H, G and S contents, whereas caffeic, ferulic and sinapic acids reduced G and S contents. These results confirm our hypothesis that exogenously applied allelochemicals are channeled into the phenylpropanoid pathway causing excessive production of lignin and its main monomers. By consequence, an enhanced stiffening of the cell wall restricts soybean root growth.     

Cyclic Phosphatidic Acid Stimulates cAMP Production and Inhibits Growth in Human Colon Cancer Cells

Colon cancer is a malignancy that develops in colon and rectal tissues. The prognosis for metastatic colon cancer remains poor, and novel therapeutic options are required to reduce colon cancer mortality. Recently, intracellular cAMP levels have been suggested to influence the behavior of cancer cells. Intriguingly, cyclic phosphatidic acid (cPA) and its structural analogs inhibit growth in many cancer cell lines, and our previous work has suggested that cPA increases cAMP production. Phosphodiesterase (PDE) type 3 isoforms PDE3A and PDE3B are expressed mainly in cardiovascular tissue and adipose tissue, respectively. Moreover, increase in intracellular cAMP levels has been associated with the inhibition of growth in colon cancer cells. These findings suggest that cPA could be used in colon cancer therapy. In this study, we found that cPA inhibited the growth of HT-29 cells, which express high levels of PDE3B, but not the growth of DLD-1 cells, which express low levels of PDE3B. Furthermore, cPA inhibited the phosphorylation of Akt in HT-29 cells in a dose-dependent fashion. Our results suggest that PDE3B expression and intracellular cAMP levels are correlated with the proliferation of colon cancer cells. These findings demonstrate for the first time that cPA may serve as a useful a molecule in targeted therapy for colon cancer.     

Complex Growth Regulator Increases Alfalfa Seed Production

The effects of thermophilic methane fermentation products on alfalfa (Medicago sativa L.) growth, nitrogen-fixing activity, and seed production were studied in pot and field experiments. Plant treatment with the preparation at the stages of stooling and flower bud formation resulted in an increase in the root nodule weight and their nitrogen-fixing activity, the accumulation of cytokinins (zeatin and zeatin riboside), and an increase in the green mass yield and protein content, especially at a low (0.25 of the full rate) mineral nitrogen rate. Crop seed production was considerably improved during the first (pot experiments) and second (field experiments) growing seasons. The conclusion was drawn that the causes for improved alfalfa seed production were the effects of group B vitamins, phytohormones, their interaction, and the switching of metabolic pathways toward cytokinin synthesis.     

肉桂酸和咖啡酸对莴苣生长的化感作用及其机理研究

该研究以莴苣为受体植物,分析了酚酸类化感物质肉桂酸和咖啡酸对莴苣幼苗生长的活性效应及其作用机理,以揭示酚酸类化合物的化感作用机制。结果显示:(1)不同浓度的肉桂酸均对莴苣幼苗根长、茎长及鲜重产生明显的抑制作用,当肉桂酸的浓度为1 000μmol/L时其对莴苣幼苗根长、茎长及鲜重的抑制率分别达到了89%、74%和49%;咖啡酸对莴苣幼苗根长和茎长均表现出低浓度(0.1、1.0和10μmol/L)促进、高浓度(100和1 000μmol/L)抑制的活性作用模式,且高浓度下肉桂酸对幼苗生长的抑制作用明显强于咖啡酸。(2)较低浓度(0.1、1.0和10μmol/L)的肉桂酸和咖啡酸对莴苣根尖细胞活力均无明显影响;高浓度(100和1 000μmol/L)的肉桂酸和咖啡酸使莴苣根尖细胞的死亡数明显增加。(3)低浓度(0.1和1.0μmol/L)的肉桂酸和较低浓度(0.1、1.0和10μmol/L)的咖啡酸对莴苣根部的活性氧积累均无明显影响;当肉桂酸处理浓度大于10μmol/L及咖啡酸处理浓度大于100μmol/L时,随着浓度的升高莴苣根部活性氧的积累大量增加。研究表明,一定浓度的肉桂酸和咖啡酸均能够诱导莴苣体内活性氧的产生和积累,并降低幼苗根尖细胞的活力,进而影响莴苣幼苗的生长发育,且肉桂酸的生长抑制作用明显强于咖啡酸。     

Characterization of delta-Aminolevulinic Acid Formation in Soybean Root Nodules

Formation of the heme precursor δ-aminolevulinic acid (ALA) was studied in soybean root nodules elicited by Bradyrhizobium japonicum. Glutamate-dependent ALA formation activity by soybean (Glycine max) in nodules was maximal at pH 6.5 to 7.0 and at 55 to 60°C. A low level of the plant activity was detected in uninfected roots and was 50-fold greater in nodules from 17-day-old plants; this apparent stimulation correlated with increases in both plant and bacterial hemes in nodules compared with the respective asymbiotic cells. The glutamate-dependent ALA formation activity was greatest in nodules from 17-day-old plants and decreased by about one-half in those from 38-day-old plants. Unlike the eukaryotic ALA formation activity, B. japonicum ALA synthase activity was not significantly different in nodules than in cultured cells, and the symbiotic activity was independent of nodule age. The lack of symbiotic induction of B. japonicum ALA synthase indicates either that ALA formation is not rate-limiting, or that ALA synthase is not the only source of ALA for bacterial heme synthesis in nodules. Plant cytosol from nodules catalyzed the formation of radiolabeled ALA from U-[¹⁴C]glutamate and 3,4-[³H]glutamate but not from 1-[¹⁴C]glutamate, and thus, operation of the C₅ pathway could not be confirmed.     

Blue Light Inhibits Mycotoxin Production and Increases Total Lipids and Pigmentation in Alternaria alternata

[This corrects the article on p. 1075 in vol. 38.].     

Oleic Acid Inhibits Gap Junction Permeability and Increases Glucose Uptake in Cultured Rat Astrocytes

Abstract: The role of oleic acid in the modulation of gap junction permeability was studied in cultured rat astrocytes by the scrape-loading/Lucifer yellow transfer technique. Incubation with oleic acid caused a dose-dependent inhibition of gap junction permeability by 79.5% at 50 µ M , and no further inhibition was observed by increasing the oleic acid concentration to 100 µ M . The oleic acid-mediated inhibition of gap junction permeability was reversible and was prevented by bovine serum albumin. The potency of oleic acid-related compounds in inhibiting gap junction permeability was arachidonic acid > oleic acid > oleyl alcohol > palmitoleic acid > stearic acid > octanol > caprylic acid > palmitic acid > methyloleyl ester. Oleic acid and arachidonic acid, but not methyloleyl ester, increased glucose uptake by astrocytes. Neither oleic acid nor arachidonic acid increased glucose uptake in the poorly coupled glioma C6 cells. These results support that the inhibition of gap junction permeability is associated with the increase in glucose uptake. We suggest that oleic acid may be a physiological mediator of the transduction pathway leading to the inhibition of intercellular communication.     

Feedback-Resistant Acetohydroxy Acid Synthase Increases Valine Production in Corynebacterium glutamicum

Acetohydroxy acid synthase (AHAS), which catalyzes the key reactions in the biosynthesis pathways of branched-chain amino acids (valine, isoleucine, and leucine), is regulated by the end products of these pathways. The whole Corynebacterium glutamicum ilvBNC operon, coding for acetohydroxy acid synthase (ilvBN) and aceto hydroxy acid isomeroreductase (ilvC), was cloned in the newly constructed Escherichia coli-C. glutamicum shuttle vector pECKA (5.4 kb, Km^r). By using site-directed mutagenesis, one to three amino acid alterations (mutations M8, M11, and M13) were introduced into the small (regulatory) AHAS subunit encoded by ilvN. The activity of AHAS and its inhibition by valine, isoleucine, and leucine were measured in strains carrying the ilvBNC operon with mutations on the plasmid or the ilvNM13 mutation within the chromosome. The enzyme containing the M13 mutation was feedback resistant to all three amino acids. Different combinations of branched-chain amino acids did not inhibit wild-type AHAS to a greater extent than was measured in the presence of 5 mM valine alone (about 57%). We infer from these results that there is a single binding (allosteric) site for all three amino acids in the enzyme molecule. The strains carrying the ilvNM13 mutation in the chromosome produced more valine than their wild-type counterparts. The plasmid-free C. glutamicum ΔilvA ΔpanB ilvNM13 strain formed 90 mM valine within 48 h of cultivation in minimal medium. The same strain harboring the plasmid pECKAilvBNC produced as much as 130 mM valine under the same conditions.     

Exogenous Glutamate Inhibits the Root Growth and Increases the Glutamine Content in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Previously, our work with ginseng hairy root shows that the tissue of low-branching and slow-growing phenotype contains high level of glutamine. In order to check if the high glutamine concentration inhibits the root growth, we applied exogenous glutamine or glutamate into growth medium and check the root growth of Arabidopsis. While glutamine did not affect root growth, over 0.1 mM glutamate inhibited severe root growth. However, when the amino acid solution was adjusted to pH 5.7 and added into medium, Arabidopsis seedlings show normal growth pattern on medium containing glutamate or aspartate. These results demonstrated that inhibition of the root growth by high concentration of exogenous glutamate was a result of the low pH toxicity caused by acidic amino acid, although low concentration (0.05 mM) of glutamate has an inhibitory effect on the primary root growth. The application of exogenous glutamine or glutamate increases glutamine concentration within root tissue about 3- to 4-fold. However, concentration of glutamate is not significantly increased. The KO mutant on each of the Gln1_1, Gln1_2, or Glu2 gene was little effective on the root growth. These results indicate that high concentration of endogenous glutamine observed in root tissue does not affect root growth.     

Allantoic Acid Synthesis in Soybean Root Nodule Cytosol via Xanthine Dehydrogenase

Allantoin and allantoic acid are the major forms of nitrogen transported from soybean nodules to other parts of the plant. Neither the pathway or the site of ureide synthesis has been demonstrated in root nodules.     

Root and Shoot Growth of Plants Treated with Abscisic Acid

Young seedlings of Capsicum annum L., Commelina communis L.and maize (Zea mays L.) were subjected to a mild water-stressingtreatment and/or treated with abscisic acid (ABA). Plants rootedin soil received a soil-drying treatment and their leaves weresprayed with a 10–⁴ M solution of ABA. Plants grown insolution culture were stressed by the addition of polyethyleneglycol (PEG) to the rooting medium and ABA was also added tothe rooting medium, either with or without PEG. The effectsof both treatments on the growth of roots and shoots and theultimate root: shoot dry weight ratio were very similar. Shootgrowth was limited both by water stress and by ABA application;while there was some evidence that mild water stress and/orABA application may have resulted in a stimulation of root growth.More severe water stress reduced the growth of roots but theoverall effect of stress was to increase the ratio of rootsto shoots. Capsicum annum L., Commelina communis L., Zea mays L., water stress, abscisic acid     

Water Deficit and Abscisic Acid Cause Differential Inhibition of Shoot versus Root Growth in Soybean Seedlings : Analysis of Growth, Sugar Accumulation, and Gene Expression

Roots often continue to elongate while shoot growth is inhibited in plants subjected to low-water potentials. The cause of this differential response to water deficit was investigated. We examined hypocotyl and root growth, polysome status and mRNA populations, and abscisic acid (ABA) content in etiolated soybean (Glycine max [L.] Merr. cv Williams) seedlings whose growth was inhibited by transfer to low-water potential vermiculite or exogenous ABA. Both treatments affected growth and dry weight in a similar fashion. Maximum inhibition of hypocotyl growth occurred when internal ABA levels (modulated by ABA application) reached the endogenous level found in the elongating zone of seedlings grown in water-deficient vermiculite. Conversely, root growth was affected to only a slight extent in low-water potential seedlings and by most ABA treatments (in some, growth was promoted). In every seedling section examined, transfer of seedlings into low-water potential vermiculite caused ABA levels to increase approximately 5- to 10-fold over that found in well-watered seedlings. Changes in soluble sugar content, polysome status, and polysome mRNA translation products seen in low-water potential seedlings did not occur with ABA treatments sufficient to cause significant inhibition of hypocotyl elongation. These data suggest that both variation in endogenous ABA levels, and differing sensitivity to ABA in hypocotyls and roots can modulate root/shoot growth ratios. However, exogenous ABA did not induce changes in sugar accumulation, polysome status, and mRNA populations seen after transfer into low-water potential vermiculite.     

Fine Root Growth Increases in Response to Nitrogen Addition in Phosphorus-limited Northern Hardwood Forests

Ecosystems - Resource allocation theory posits that increased soil nutrient availability results in decreased plant investment in nutrient acquisition. We evaluated this theory by quantifying fine...     

Acid Protease Production by Fungi Used in Soybean Food Fermentation

Growth conditions for maximum protease production by Rhizopus oligosporus, Mucor dispersus, and Actinomucor elegans, used in Oriental food fermentations, were investigated. Enzyme yields by all three fungi were higher in solid substrate fermentations than in submerged culture. The level of moisture in solid substrate must be at about 50 to 60%. Very little growth of these fungi was noted when the moisture of substrate was below 35%, whereas many fungi including most storage fungi generally grow well on solid substrate with that level of moisture. Among the three substrates tested—wheat bran, wheat, and soybeans—wheat bran was the most satisfactory one for enzyme production. The optimal conditions for maximum enzyme production of the three fungi grown on wheat bran were: R. oligosporus, 50% moisture at 25 C for 3 to 4 days; M. dispersus, 50 to 63% moisture at 25 C for 3 to 4 days; A. elegans, 50 to 63% moisture at 20 C for 3 days. Because these fungi are fast growing and require high moisture for growth and for enzyme synthesis, the danger of contamination by toxin-producing fungi would be minimal.     

Al Inhibits Both Shoot Development and Root Growth in als3, an Al-Sensitive Arabidopsis Mutant

In als3, an Al-sensitive Arabidopsis mutant, shoot development and root growth are sensitive to Al. Mutant als3 seedlings grown in an Al-containing medium exhibit severely inhibited leaf expansion and root growth. In the presence of Al, unexpanded leaves accumulate callose, an indicator of Al damage in roots. The possibility that the inhibition of shoot development in als3 is due to the hyperaccumulation of Al in this tissue was examined. However, it was found that the levels of Al that accumulated in shoots of als3 are not different from the wild type. The inhibition of shoot development in als3 is not a consequence of nonspecific damage to roots, because other metals (e.g. LaCl3 or CuSO4) that strongly inhibit root growth did not block shoot development in als3 seedlings. Al did not block leaf development in excised als3 shoots grown in an Al-containing medium, demonstrating that the Al-induced damage in als3 shoots was dependent on the presence of roots. This suggests that Al inhibition of als3 shoot development may be a delocalized response to Al-induced stresses in roots following Al exposure.     

The Weak Acid Preservative Sorbic Acid Inhibits Conidial Germination and Mycelial Growth of Aspergillus niger through Intracellular Acidification

The growth of the filamentous fungus Aspergillus niger, a common food spoilage organism, is inhibited by the weak acid preservative sorbic acid (trans-trans-2,4-hexadienoic acid). Conidia inoculated at 10⁵/ml of medium showed a sorbic acid MIC of 4.5 mM at pH 4.0, whereas the MIC for the amount of mycelia at 24 h developed from the same spore inoculum was threefold lower. The MIC for conidia and, to a lesser extent, mycelia was shown to be dependent on the inoculum size. A. niger is capable of degrading sorbic acid, and this ability has consequences for food preservation strategies. The mechanism of action of sorbic acid was investigated using ³¹P nuclear magnetic resonance (NMR) spectroscopy. We show that a rapid decline in cytosolic pH (pH_cyt) by more than 1 pH unit and a depression of vacuolar pH (pH_vac) in A. niger occurs in the presence of sorbic acid. The pH gradient over the vacuole completely collapsed as a result of the decline in pH_cyt. NMR spectra also revealed that sorbic acid (3.0 mM at pH 4.0) caused intracellular ATP pools and levels of sugar-phosphomonoesters and -phosphodiesters of A. niger mycelia to decrease dramatically, and they did not recover. The disruption of pH homeostasis by sorbic acid at concentrations below the MIC could account for the delay in spore germination and retardation of the onset of subsequent mycelial growth.     

Effect of Increases in Oxygen Concentration during the Argon-Induced Decline in Nitrogenase Activity in Root Nodules of Soybean

When intact nodulated roots of soybean (Glycine max L. Merr. nodulated with Bradyrhizobium japonicum strain USDA 16) were exposed to an atmosphere lacking N₂ gas (Ar:O₂ 80:20), total nitrogenase activity (measured as H₂ evolution) and respiration (CO₂ evolution) declined with time of exposure. In Ar-inhibited nodules, when the O₂ concentration in the rhizosphere was increased in a linear `ramp' of 2.7% per minute, 93% of the original H₂ evolution and 99% of the CO₂ evolution could be recovered. The internal nodule O₂ concentration (estimated from leghemoglobin oxygenation) declined to 56% of its initial value after 60 minutes of Ar:O₂ exposure and could be partially recovered by the linear increases in O₂ concentration. Nodule gas permeability, as estimated from the lag in ethylene production following exposure of nodules to acetylene, decreased to 26% of its initial value during the Ar-induced decline. Collectively, the results provide direct evidence that the Ar-induced decline results from decreased nodule gas permeability and indicate that the decline in permeability, rather than being immediate, occurs gradually over the period of Ar:O₂ exposure.     

Production of Siderophores Increases Resistance to Fusaric Acid in Pseudomonas protegens Pf-5

Fusaric acid is produced by pathogenic fungi of the genus Fusarium, and is toxic to plants and rhizobacteria. Many fluorescent pseudomonads can prevent wilt diseases caused by these fungi. This study was undertaken to evaluate the effect of fusaric acid on P. protegens Pf-5 and elucidate the mechanisms that enable the bacterium to survive in the presence of the mycotoxin. The results confirm that fusaric acid negatively affects growth and motility of P. protegens. Moreover, a notable increase in secretion of the siderophore pyoverdine was observed when P. protegens was grown in the presence of fusaric acid. Concomitantly, levels of enzymes involved in the biosynthesis of pyoverdine and enantio-pyochelin, the second siderophore encoded by P. protegens, increased markedly. Moreover, while similar levels of resistance to fusaric acid were observed for P. protegens mutants unable to synthesize either pyoverdine or enanto-pyochelin and the wild type strain, a double mutant unable to synthesize both kinds of siderophores showed a dramatically reduced resistance to this compound. This reduced resistance was not observed when this mutant was grown under conditions of iron excess. Spectrophotometric titrations revealed that fusaric acid binds not only Fe²⁺ and Fe³⁺, but also Zn²⁺, Mn²⁺ and Cu²⁺, with high affinity. Our results demonstrate that iron sequestration accounts at least in part for the deleterious effect of the mycotoxin on P. protegens.