Upendra N. Dwivedi

Delayed ripening of banana fruit by salicylic acid

Salicylic acid treatment has been found to delay the ripening of banana fruits (Musa acuminata). Fruit softening, pulp:peel ratio, reducing sugar content, invertase and respiration rate have been found to decrease in salicylic acid treated fruits as compared with control ones. The activities of major cell wall degrading enzymes, viz. cellulase, polygalacturonase and xylanase were found to be decreased in presence of salicylic acid. The major enzymatic antioxidants namely, catalase and peroxidase, were also found to be decreased in presence of salicylic acid during banana fruit ripening.

Synthesis of phytochelatins and modulation of antioxidants in response to cadmium stress in Cuscuta reflexa--an angiospermic parasite.

Effect of cadmium on growth, antioxidative enzymes namely catalase, peroxidase, glutathione reductase, level of glutathione and phytochelatin synthesis was investigated in callus and seedlings of Cuscuta reflexa. A time, concentration and tissue dependent response of Cd was observed. Cd inhibited the growth of callus and seedlings by 50% at 300 and 500 micromol/L concentrations, respectively. Shorter exposure of low concentration of Cd led to augmentation of antioxidant activity, both in callus and seedlings, while longer exposure and high concentration of Cd led to a concentration dependent decrease in callus. Analysis of phytochelatin (PC) synthesis in callus and seedlings of C. reflexa revealed both quantitative and qualitative changes. Cd at low concentrations led to synthesis of predominantly PC4, while at higher concentrations, PC3 was the major form being synthesized. Amelioration of antioxidative systems of C. reflexa in response to Cd stress might be playing a protective role, alleviating the damaging effects of ROS, generated during Cd stress. Concomitantly, chelation and sequestering of toxic Cd ions in this parasite was mediated by synthesis of PC. The response to Cd stress shown by this holoparasitic plant was found to be similar to those of non-parasitic plants (hosts).

Salicylic acid modulates glutathione metabolism in pea seedlings

Summary Salicylic acid has been shown to play an important role in plant defence responses to pathogen attack. Earlier studies have demonstrated that one of the mechanisms of action of salicylic acid is the inhibition of catalase, resulting in elevated levels of H 2 O 2 , which activates defence related genes. In the present study, we investigated the effect of salicylic acid on some important enzymes associated with oxidative stress, namely catalase, peroxidase and glutathione reductase, along with the status of glutathione in pea seedlings. Salicylic acid treatment resulted, in a concentration-dependent manner, in decreased levels of catalase and peroxidase concomitant with an increase in the level of glutathione reductase. Investigation of the effect of salicylic acid on soluble protein profile revealed gradual depletion of polypeptides on SDS-PAGE corresponding to those of catalase and peroxidase in a concentration-dependent manner, suggesting that salicylic acid also affects expression and/or turnover of catalase and peroxidase. Measurement of glutathione levels in response to salicylic acid treatment revealed an increase in the reduced glutathione (GSH) content and a decrease in the oxidized glutathione (GSSG), along with an increased GSH: GSSG ratio. The data suggest that salicylic acid mediated inactivation of catalase and peroxidase results in a concomitant increase in glutathione reductase along with an increased GSH: GSSG ratio. This increase might protect the cell against oxidative damage by the increased H 2 O 2 level upon salicylic acid treatment.

Alzheimer's disease: An overview of amyloid beta dependent pathogenesis and its therapeutic implications along with in silico approaches emphasizing the role of natural products

Alzheimers disease (AD) is a progressive and irreversible neurodegenerative disorder characterized by amyloid beta (Aβ) deposition in brain with subsequent formation of neuritic plaques leading to dementia. A number of therapeutic strategies targeted against Aβ depositions have been rigorously explored which provided successful results corresponding to the existing symptomatic treatments. However, at the same time, several failures corresponding to the disease altering therapies and drugs have also been observed due to potential drawbacks in understanding of the pathogenesis of the disease, development of drug candidates and subsequent designing of clinical trials. Preclinical research, along with experimental and clinical studies, is continuously providing novel information which may reveal multi-target directed ligands and combination therapies for targeting Aβ. Thus, in view of the estimated increase in the number of AD patients globally, the present review attempts to summarize the available evidence dealing with various therapeutic approaches targeting Aβ, focusing specifically on pharmaceutical compounds under various stages of clinical trials. Furthermore, in view of a number of computational advances having significant impact in the field of computer aided drug design, we have also presented results of analysis of natural compounds as potential therapeutic molecules in preventing Aβ plaque formation using in silico approaches.

Nitrogen Assimilation in Germinating Phaseolus aureus Seeds Under Saline Stress

Summary The developmental patterns of nitrate reductase, glutamate dehydrogenase, glutamate synthase, glutamine synthetase and soluble protein were investigated and compared in root and shoot portions of germinating green gram seeds both in the absence and presence of different concentrations of sodium chloride. The activity of all these enzymes initially increased gradually until day 4 of germination and thereafter declined under all conditions in both root and shoot tissues. In the presence of NaCl the activity levels each of nitrate reductase, glutamine synthetase and glutamate synthase were found to increase over that of the control (in absence of NaCl). Increasing the concentration of NaCl caused a further increase in the levels of these enzymes throughout the germination period in a concentration-dependent manner. On the other hand, glutamate dehydrogenase activity decreased in the presence of NaCl, and increasing concentrations of NaCl caused a further decline in the level of enzyme throughout. Saline treatment inhibited the rate of protein depletion in both shoot and root tissues throughout germination. The results indicate that the glutamine synthetase/glutamate synthase pathway of ammonia assimilation becomes operative under conditions of saline stress.

Down-regulation of lignin biosynthesis in transgenic Leucaena leucocephala harboring O-methyltransferase gene.

In the present study, a 0.47 kb OMT gene construct from aspen, encoding for an enzyme O-methyltransferase (OMT, EC 2.1.1.6), in antisense orientation was used to down-regulate lignin biosynthesis in Leucaena leucocephala. The plants were transformed with Agrobacterium tumefaciens strain harboring the antisense gene, and the transformation was confirmed by PCR amplification of the npt II gene. The integration of a heterologous antisense OMT gene construct in transformed plants led to a maximum of 60% reduction in OMT activity relative to control. The evaluation of total lignin content by the Klason method revealed a maximum of 28% reduction. Histochemical analyses of stem sections depicted a reduction in lignin content and normal xylem development. The results also suggested a probable increase in aldehyde levels and a decrease in syringyl units. Lignin down-regulation was accompanied by an increase in methanol soluble phenolics to an extent that had no impact on wood discoloration, and the plants displayed a normal phenotype. Concomitantly, an increase of up to 9% in cellulose content was also observed. Upon alkali extraction, modified lignin was more extractable as evident from reduced Klason lignin in saponified residue and increased alkali soluble phenolics. The results together suggested that the extent of down-regulation of OMT activity achieved may lead to quality amelioration of Leucaena with respect to its applicability in pulp and paper manufacture as well as nutritive and easily digestible forage production.

SlERF36, an EAR-motif-containing ERF gene from tomato, alters stomatal density and modulates photosynthesis and growth

The AP2 domain class of transcription factors is a large family of genes with various roles in plant development and adaptation but with very little functional information in plants other than Arabidopsis. Here, the characterization of an EAR motif-containing transcription factor, SlERF36, from tomato that affects stomatal density, conductance, and photosynthesis is described. Heterologous expression of SlERF36 under the CaMV35S promoter in tobacco leads to a 25–35% reduction in stomatal density but without any effect on stomatal size or sensitivity. Reduction in stomatal density leads to a marked reduction in stomatal conductance (42–56%) as well as transpiration and is associated with reduced CO2 assimilation rates, reduction in growth, early flowering, and senescence. A prominent adaptive response of SlERF36 overexpressors is development of constitutively high non-photochemical quenching (NPQ) that might function as a protective measure to prevent damage from high excitation pressure. The high NPQ leads to markedly reduced light utilization and low electron transport rates even at low light intensities. Taken together, these data suggest that SlERF36 exerts a negative control over stomatal density and modulates photosynthesis and plant development through its direct or indirect effects.

C-Phycocyanin: An effective protective agent against thymic atrophy by tributyltin

Spirulina platensis, used worldwide as a food supplement, is a natural source of protein, vitamins, carbohydrates and polyunsaturated fatty acids. C-Phycocyanin (C-Pc), its major biliprotein, is known to possess anti-oxidant, anti-inflammatory and radical scavenging properties. Our present study showed that treatment with C-Pc protects the rats from Tributyltin (TBT) induced thymic atrophy. The results reveal TBT-induced oxidative stress mediated apoptosis in rat thymocytes in vivo and its attenuation by C-Pc. This ameliorative effect could be attributed to antioxidant activity of the biliprotein. C-Pc also increased TBTC reduced thymic weight and cellularity as well. TBTC-induced ROS generation and lowered GSH levels were restored by C-Pc, suggesting its radical scavenging properties. The various apoptotic determinants such as mitochondrial membrane potential, Bax/Bcl-2 ratio, caspase-3 activity and apoptotic cell population were effectively modulated by C-Pc treatment. We make this first observation to illustrate the effectiveness of C-Pc in reducing TBTC-induced thymic atrophy. The morphology of thymic tissue was restored to near normal by this biliprotein. The present study, therefore, suggests that C-Pc could serve as an effective natural antioxidant for efficient management of TBTC induced oxidative damage.

Immobilization of papaya laccase in chitosan led to improved multipronged stability and dye discoloration

A purified papaya laccase was immobilized in chitosan beads using entrapment approach and its physico-chemical properties were investigated and compared with that of free enzyme. Increase in properties of the laccase such as optimum temperature (by 10 °C), thermostability (by 3-folds) and optimum pH (from 8.0 to 10.0) was observed after immobilization. Immobilization led to increased tolerance of enzyme to a number of metal ions (including heavy metals) and organic solvents namely, ethanol, isopropanol, methanol, benzene and DMF. The catalytic efficiency (Kcat/Km) of the immobilized enzyme was found to increase more than ten folds, in comparison to that of the free enzyme, with hydroquinone as substrate. Immobilization of laccase also led to improvement in dye decolorization such that the synthetic dye indigo carmine (50 μg/ml) was completely decolorized within 8h of incubation as compared to that of the free laccase which decolorized the same dye to only 56% under similar conditions. Thus, immobilization of laccase into chitosan beads led to tremendous improvement in various useful attributes of this enzyme thereby making it more versatile for its industrial exploitation.

Modulation of mango ripening by chemicals: physiological and biochemical aspects

During ripening, fleshy fruits undergo textural changes that lead to loss of tissue firmness and consequent softening due to cell wall dismantling carried out by different and specifically expressed enzymes. The effect of various chemical treatments on the ripening of mango fruit (Mangifera indica) was investigated at physiological and biochemical level. Based on changes in respiration, firmness, pH, total soluble sugar and a cell wall degrading enzyme pectate lyase (PEL) activity, treatment with 1-methylcyclopropene (1-MCP), silver nitrate (AgNO3), gibberlic acid (GA3), sodium metabisulphite (SMS) and ascorbic acid led to delaying of ripening process while those of ethrel and calcium chloride (CaCl2) enhanced the process. PEL of mango was found to be inhibited by certain metabolites present in dialysed ammonium sulphate enzyme extract as well as EDTA. Mango PEL activity exhibited an absolute requirement for Ca2+ and an optimum pH of 8.5.