Correction to: Sodium nitroprusside enhances biomass and gymnemic acids production in cell suspension of Gymnema sylvestre (Retz.) R.Br. ex. Sm.

Plant Cell, Tissue and Organ Culture (PCTOC) -     

Biological nitrification inhibition (BNI) activity in sorghum and its characterization

Aims

The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that includes inhibitor production, their chemical identity, functionality and factors regulating their release.

Methods

Sorghum was grown in solution culture and root exudate was collected using aerated NH₄Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided chromatographic fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release.

Results

Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATU?g^?1 root dwt. d^?1. Addition of hydrophilic BNIs (10 ATU?g^?1 soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated are: sakuranetin (ED₈₀ 0.6 μM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED₈₀ 13.0 μM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH ₄ ⁺ in the root environment and the stimulatory effect of NH ₄ ⁺ lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED₅₀ 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED₅₀ 100 μM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay.

Conclusions

There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.     

Modifying bio-catalytic properties of enzymes for efficient biocatalysis: a review from immobilization strategies viewpoint

Enzyme-based catalysis has become one of the most important disciplines in organic synthesis and plays a noteworthy role in the establishment of many chemical industries, e.g. fine chemicals, food or energy, textiles, agricultural, cosmeceutical, medicinal and pharmaceutical industries. However, pristine enzymes fail to demonstrate requisite functionalities for an industrial setting where extremely specific and stable catalysts are required. Immobilization enhances the catalytic stability and activity of enzymes and trims the overall cost burden of the enzyme. Therefore, it widely endeavours for proficient, sustainable, and environmentally responsive catalytic processes. Amongst several immobilization strategies, e.g. (1) supports-assisted, i.e. physical or covalent coupling and (2) supports-free techniques, i.e. cross-linked enzyme crystals (CLECs) or aggregates are the most promising ones and widely pursued for enzyme immobilization purposes. This perspective review focuses on up-to-date developments in the area of enzyme immobilization and presents their potentialities to upgrade and/or modify enzyme properties. Both types of immobilization strategies, i.e. supports-assisted and supports-free techniques are discussed with particular reference to CLECs or aggregates and protein-coated microcrystals. Also, several useful traits achieved after immobilization are also discussed in the second half of the review.     

RhoGDI facilitates geranylgeranyltransferase-I-mediated RhoA prenylation

Protein prenylation is a post-translational modification where farnesyl or geranylgeranyl groups are enzymatically attached to a C-terminal cysteine residue. This modification is essential for the activity of small cellular GTPases, as it allows them to associate with intracellular membranes. Dissociated from membranes, prenylated proteins need to be transported through the aqueous cytoplasm by protein carriers that shield the hydrophobic anchor from the solvent. One such carrier is Rho GDP dissociation inhibitor (RhoGDI). Recently, it was shown that prenylated Rho proteins that are not associated with RhoGDI are subjected to proteolysis in the cell. We hypothesized that the role of RhoGDI might be not only to associate with prenylated proteins but also to regulate the prenylation process in the cell. This idea is supported by the fact that RhoGDI binds both unprenylated and prenylated Rho proteins with high affinity in vitro, and hence, these interactions may affect the kinetics of prenylation. We addressed this question experimentally and found that RhoGDI increased the catalytic efficiency of geranylgeranyl transferase-I in RhoA prenylation. Nevertheless, we did not observe formation of a ternary RhoGDI∗RhoA∗GGTase-I complex, indicating sequential operation of geranylgeranyltransferase-I and RhoGDI. Our results suggest that RhoGDI accelerates Rho prenylation by kinetically trapping the reaction product, thereby increasing the rate of product release.     

Growth inhibition and induction of differentiation and apoptosis mediated by sodium butyrate in caco-2 cells with algal glycolipids

Summary Glycolipids should have potential effects as antitumor agents. However, very few studies have examined this property of digalactosyl diacylglycerol (DGDG) and sulfoquinovosyl diacylglycerol (SQDG) on colon cancer cells. Cell viability was determined every 24 h with sodium 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2, 4-disulfophenyl)-2H-tetrazolium dye reduction assay up to 72 h. Alkaline phosphatase activity was measured for assessing cell differentiation. Apoptosis was tested with enzyme-linked immunosorbent assay analysis. Growth of Caco-2 cells was inhibited apparently at 48 h after addition of SQDG and at 72 h with DGDG. Alkaline phosphatase activity of Caco-2 cells obviously increased in combination with DGDG or SQDG and sodium butyrate (NaBT) at 72 h, indicating that DGDG and SQDG enhanced cell differentiation induced with NaBT. An increased enrichment factor was found when the cell was treated in combination with DGDG or SQDG and NaBT. These results strongly suggest that DGDG and SQDG should be considered as the leading compounds of potentially useful colon cancer chemotherapy agents when NaBT is combined.     

Effect of polyunsaturated fatty acid-enriched phosphatidylcholine and phosphatidylserine on butyrate-induced growth inhibition, differentiation and apoptosis in Caco-2 cells

Phospholipids are fascinating in terms of important bio-functional compounds. The present work investigated the effect of polyunsaturated phosphatidylcholine (PC) and phosphatidylserine (PS) on butyrate-induced growth inhibition, differentiation and apoptosis using Caco-2 cells. Growth inhibition of Caco-2 cells became apparent 24 h after addition of PC while it took 48 h with PS. Alkaline phosphatase activity of Caco-2 cells increased with combined PC or PS and sodium butyrate (NaBT) at 72 h, indicating that PC and PS enhanced cell differentiation in the presence of NaBT. An increased enrichment factor was also found when cells were treated with combinations of PC or PS and NaBT. These results suggest that marine PC and PS can be considered to be potentially useful colon cancer chemotherapy agents with high bio-availability.     

DIMINUTO 1 affects the lignin profile and secondary cell wall formation in Arabidopsis

Brassinosteroids (BRs) play a crucial role in plant growth and development and DIMINUTO 1 (DIM1), a protein involved in BR biosynthesis, was previously identified as a cell elongation factor in Arabidopsis thaliana. Through promoter expression analysis, we showed that DIM1 was expressed in most of the tissue types in seedlings and sectioning of the inflorescence stem revealed that DIM1 predominantly localizes to the xylem vessels and in the interfascicular cambium. To investigate the role of DIM1 in cell wall formation, we generated loss-of-function and gain-of-function mutants. Disruption of the gene function caused a dwarf phenotype with up to 38 and 23% reductions in total lignin and cellulose, respectively. Metabolite analysis revealed a significant reduction in the levels of fructose, glucose and sucrose in the loss-of-function mutant compared to the wild type control. The loss-of-function mutant also had a lower S/G lignin monomer ratio relative to wild type, but no changes were detected in the gain-of-function mutant. Phloroglucinol and toluidine blue staining showed a size reduction of the vascular apparatus with smaller and disintegrated xylem vessels in the inflorescence stem of the loss-of-function mutant. Taken together, these data indicate a role for DIM1 in secondary cell wall formation. Moreover, this study demonstrated the potential role of BR hormones in modulating cell wall structure and composition.     

Cannabinoids Facilitate the Swallowing Reflex Elicited by the Superior Laryngeal Nerve Stimulation in Rats

Cannabinoids have been reported to be involved in affecting various biological functions through binding with cannabinoid receptors type 1 (CB1) and 2 (CB2). The present study was designed to investigate whether swallowing, an essential component of feeding behavior, is modulated after the administration of cannabinoid. The swallowing reflex evoked by the repetitive electrical stimulation of the superior laryngeal nerve in rats was recorded before and after the administration of the cannabinoid receptor agonist, WIN 55-212-2 (WIN), with or without CB1 or CB2 antagonist. The onset latency of the first swallow and the time intervals between swallows were analyzed. The onset latency and the intervals between swallows were shorter after the intravenous administration of WIN, and the strength of effect of WIN was dose-dependent. Although the intravenous administration of CB1 antagonist prior to intravenous administration of WIN blocked the effect of WIN, the administration of CB2 antagonist did not block the effect of WIN. The microinjection of the CB1 receptor antagonist directly into the nucleus tractus solitarius (NTS) prior to intravenous administration of WIN also blocked the effect of WIN. Immunofluorescence histochemistry was conducted to assess the co-localization of CB1 receptor immunoreactivity to glutamic acid decarboxylase 67 (GAD67) or glutamate in the NTS. CB1 receptor was co-localized more with GAD67 than glutamate in the NTS. These findings suggest that cannabinoids facilitate the swallowing reflex via CB1 receptors. Cannabinoids may attenuate the tonic inhibitory effect of GABA (gamma-aminobuteric acid) neurons in the central pattern generator for swallowing.     

FTIR study of the photoinduced processes of plant phytochrome phyA using isotope-labeled bilins and density functional theory calculations

Fourier transform infrared spectroscopy was used to analyze the chromophore structure in the parent states Pr and Pfr of plant phytochrome phyA and the respective photoproducts lumi-R and lumi-F. The spectra were obtained from phyA adducts assembled with either uniformly or selectively isotope-labeled phytochromobilin and phycocyanobilin. The interpretation of the experimental spectra is based on the spectra of chromophore models calculated by density functional theory. Global ¹³C-labeling of the tetrapyrrole allows for the discrimination between chromophore and protein bands in the Fourier transform infrared difference spectra. All infrared difference spectra display a prominent difference band attributable to a stretching mode with large contributions from the methine bridge between the inner pyrrole rings (B-C stretching). Due to mode coupling, frequencies and isotopic shifts of this mode suggest that the Pr chromophore may adopt a distorted ZZZssa or ZZZasa geometry with a twisted A-B methine bridge. The transition to lumi-R is associated with only minor changes of the amide I bands indicating limited protein structural changes during the isomerization site of the C-D methine bridge. Major protein structural changes occur upon the transition to Pfr in which the chromophore adopts a ZZEssa or ZZEasa-like state. In addition, specific interactions with the protein alter the structure of the B-C methine bridge as concluded from the substantial downshift of the respective stretching mode. These interactions are removed during the photoreaction to lumi-F (ZZE→ZZZ), which involves only small protein structural changes.