Michael Gabriel Paulraj

Mechanisms of plant defense against insect herbivores

Plants respond to herbivory through various morphological, biochemicals, and molecular mechanisms to counter/offset the effects of herbivore attack. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by induced responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be engineered genetically, so that the defensive compounds are constitutively produced in plants against are challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.

Insulin sensitization via partial agonism of PPARγ and glucose uptake through translocation and activation of GLUT4 in PI3K/p-Akt signaling pathway by embelin in type 2 diabetic rats.

BACKGROUND The present study was aimed at isolating an antidiabetic molecule from a herbal source and assessing its mechanism of action. METHODS Embelin, isolated from Embelia ribes Burm. (Myrsinaceae) fruit, was evaluated for its potential to regulate insulin resistance, alter β-cell dysfunction and modulate key markers involved in insulin sensitivity and glucose transport using high-fat diet (HFD) fed-streptozotocin (STZ) (40mg/kg)-induced type 2 diabetic rats. Molecular-dockings were performed to investigate the binding modes of embelin into PPARγ, PI3K, p-Akt and GLUT4 active sites. RESULTS Embelin (50mg/kg b wt.) reduced body weight gain, blood glucose and plasma insulin in treated diabetic rats. It further modulated the altered lipid profiles and antioxidant enzymes with cytoprotective action on β-cell. Embelin significantly increased the PPARγ expression in epididymal adipose tissue compared to diabetic control group; it also inhibited adipogenic activity; it mildly activated PPARγ levels in the liver and skeletal muscle. It also regulated insulin mediated glucose uptake in epididymal adipose tissue through translocation and activation of GLUT4 in PI3K/p-Akt signaling cascade. Embelin bound to PPARγ; it disclosed stable binding affinities to the active sites of PI3K, p-Akt and GLUT4. CONCLUSIONS These findings show that embelin could improve adipose tissue insulin sensitivity without increasing weight gain, enhance glycemic control, protect β-cell from damage and maintain glucose homeostasis in adipose tissue. GENERAL SIGNIFICANCE Embelin can be used in the prevention and treatment of type 2 diabetes mellitus caused due to obesity.

Solanum torvum Swartz. fruit containing phenolic compounds shows antidiabetic and antioxidant effects in streptozotocin induced diabetic rats

In this study, quantification of phenolic compounds and the investigation of antidiabetic and antioxidant activities of the fruit of Solanum torvum Swartz. are described. S. torvum fruit methanol extract (STMe) was administered orally at a dose of 200 and 400mg/kg/day to streptozotocin induced diabetic rats for 30days. The levels of glucose, insulin, total protein, hemoglobin, glycated hemoglobin, liver glycogen and marker enzymes of carbohydrate metabolism, hepatic function and antioxidants were analyzed. High-performance liquid chromatography (HPLC) analysis revealed that STMe contained high levels of phenolic compounds, mainly rutin (1.36%w/w), caffeic acid (12.03%w/w), gallic acid (4.78%w/w) and catechin (0.46%w/w). STMe at 200 and 400mg/kg reduced blood glucose level by 17.04% and 42.10%, respectively in diabetic rats. The levels and/or activities of other biochemical parameters were restored significantly compared to diabetic control rats due to treatment with fruit extract. Histology of liver and pancreas in STMe treated groups substantiated the cytoprotective action of the drug. Immunohistochemical observation of islets in extract treated diabetic rats showed apparent β-cells regeneration. These findings suggest that S. torvum fruit containing phenolic compounds has great potential as a natural source of antidiabetic and antioxidant drug.

Hypoglycemic and β-cells regenerative effects of Aegle marmelos (L.) Corr. bark extract in streptozotocin-induced diabetic rats

The aim of this study was to examine the antidiabetic potential of Aegle marmelos (L.) Corr. (Rutaceae) bark in a diabetic rat model. Dose dependent effects of methanol extract of Aegle marmelos bark (AM) (200 and 400 mg/kg) on blood glucose, plasma insulin, glycated haemoglobin (HbA1c), total protein, hepatic glycogen, marker enzymes of hepatic function and carbohydrate metabolism were evaluated in (streptozotocin) STZ-induced diabetic rats by oral administration for 30 days. Structural integrity of pancreatic islets was assessed by routine histology while, their functional status was assessed by immunolocalization for insulin. High-performance liquid chromatography (HPLC) study established that AM contained antihyperglycemic constituents, aegelin (1.27% w/w) and lupeol (0.29% w/w). AM at 200 and 400 mg/kg showed significant reduction in blood glucose level by 19.14% and 47.32%, respectively in diabetic rats. AM treatment significantly increased insulin level, and produced similar effects on other biochemical parameters. Histological studies showed the regenerative effect of AM on the β-cells of diabetic rats. Immunohistochemical observations in the extract treated diabetic rats showed increased insulin-immunoreactive β-cells. These findings suggest that A. marmelos bark extract has the therapeutic potential in STZ-induced hyperglycemia; hence it can be used in the treatment of diabetes mellitus.

Role of salicylic acid in induction of plant defense system in chickpea (Cicer arietinum L.)

Salicylic acid (SA), a plant hormone plays an important role in induction of plant defense against a variety of biotic and abiotic stresses through morphological, physiological and biochemical mechanisms. A series of experiments were carried out to evaluate the biochemical response of the chickpea (Cicer arietinum L.) plants to a range of SA concentrations (1, 1.5, and 2 mM). Water treated plants were maintained as control. Activities of peroxidase (POD) and polyphenol oxidase (PPO) were evaluated and amounts of total phenols, hydrogen peroxide (H2O2), and proteins were calculated after 96 h of treatment. Plants responded very quickly to SA at 1.5 mM and showed higher induction of POD and PPO activities, besides the higher accumulation of phenols, H2O2 and proteins. Plants treated with SA at 2 mM showed phytotoxic symptoms. These results suggest that SA at 1.5 mM is safe to these plants and could be utilized for the induction of plant defense.

Herbivore induced plant volatiles: Their role in plant defense for pest management

Plants respond to herbivory through different defensive mechanisms. The induction of volatile emission is one of the important and immediate response of plants to herbivory. Herbivore-induced plant volatiles (HIPVs) are involved in plant communication with natural enemies of the insect herbivores, neighboring plants, and different parts of the damaged plant. Release of a wide variety of HIPVs in response to herbivore damage and their role in plant-plant, plant-carnivore and intraplant communications represents a new facet of the complex interactions among different trophic levels. HIPVs are released from leaves, flowers, and fruits into the atmosphere or into the soil from roots in response to herbivore attack. Moreover, HIPVs act as feeding and/or oviposition deterrents to insect pests. HIPVs also mediate the interactions between the plants and the microorganisms. This review presents an overview of HIPVs emitted by plants, their role in plant defense against herbivores and their implications for pest management.

Antihyperglycemic activity and antidiabetic effect of methyl caffeate isolated from Solanum torvum Swartz. fruit in streptozotocin induced diabetic rats

Natural remedies from medicinal plants are considered to be effective and safe alternatives to treat diabetes mellitus. Solanum torvum Swartz. fruit is widely used in the traditional system of medicine to treat diabetes. In the present study methyl caffeate, isolated from S. torvum fruit, was screened for its efficacy in controlling diabetes in animal models. Antihyperglycemic effect of methyl caffeate was studied in normal glucose-fed rats. The effects of oral administration of methyl caffeate (10, 20 and 40 mg/kg) for 28 days on body weight, fasting blood glucose, plasma insulin, hemoglobin, glycated hemoglobin, total protein, hepatic glycogen and carbohydrate metabolism enzymes in streptozotocin induced diabetic rats were investigated. Histological observations in the pancreas and GLUT4 expression in skeletal muscles were also studied. Methyl caffeate at 40 mg/kg significantly prevented the increase in blood glucose level after glucose administration at 60 min in comparison to the hyperglycemic control group. In streptozotocin induced diabetic rats, methyl caffeate produced significant reduction in blood glucose and increased body weight. The levels and/or activities of other biochemical parameters were near normal due to treatment with methyl caffeate. Methyl caffeate treated diabetic rats showed upregulation of GLUT4 and regeneration of β-cells in the pancreas. These results substantiated that methyl caffeate possessed hypoglycemic effect, and it could be developed into a potent oral antidiabetic drug.

Gallic acid attenuates high-fat diet fed-streptozotocin-induced insulin resistance via partial agonism of PPARγ in experimental type 2 diabetic rats and enhances glucose uptake through translocation and activation of GLUT4 in PI3K/p-Akt signaling pathway

In this study, the therapeutic efficacy of gallic acid from Cyamopsis tetragonoloba (L.) Taub. (Fabaceae) beans was examined against high-fat diet fed-streptozotocin-induced experimental type 2 diabetic rats. Molecular-dockings were done to determine the putative binding modes of gallic acid into the active sites of key insulin-signaling markers. Gallic acid (20 mg/kg) given to high-fat diet fed-streptozotocin-induced rats lowered body weight gain, fasting blood glucose and plasma insulin in diabetic rats. It further restored the alterations of biochemical parameters to near normal levels in diabetic treated rats along with cytoprotective action on pancreatic β-cell. Histology of liver and adipose tissues supported the biochemical findings. Gallic acid significantly enhanced the level of peroxisome proliferator-activated receptor γ (PPARγ) expression in the adipose tissue of treated rat compared to untreated diabetic rat; it also slightly activated PPARγ expressions in the liver and skeletal muscle. Consequently, it improved insulin-dependent glucose transport in adipose tissue through translocation and activation of glucose transporter protein 4 (GLUT4) in phosphatidylinositol 3-kinase (PI3K)/phosphorylated protein kinase B (p-Akt) dependent pathway. Gallic acid docked with PPARγ; it exhibited promising interactions with the GLUT4, glucose transporter protein 1 (GLUT1), PI3K and p-Akt. These findings provided evidence to show that gallic acid could improve adipose tissue insulin sensitivity, modulate adipogenesis, increase adipose glucose uptake and protect β-cells from impairment. Hence it can be used in the management of obesity-associated type 2 diabetes mellitus.

Larvicidal, Ovicidal, and Repellent Activities of Marine Sponge Cliona celata (Grant) Extracts against Culex quinquefasciatus Say and Aedes aegypti L. (Diptera: Culicidae)

Solvent extracts of marine sponge Cliona celata (Grant) were screened for larvicidal, ovicidal, and repellent properties against the filarial vector Culex quinquefasciatus Say and dengue vector Aedes aegypti L. Larvicidal and ovicidal activities of hexane, ethyl acetate, and methanol extracts were tested in four different concentrations ranging as 62.5, 125, 250, and 500 ppm. Among the three solvent extracts of C. celata, methanol extract showed the highest larvicidal activity at 500 ppm against both mosquito species. The LC50 and LC90 values of C. celata methanol extract were recorded as 95.63 and 242.16 ppm against C. quinquefasciatus larvae and 158.40 and 780.16 ppm against A. aegypti larvae, respectively. Ovicidal activity was high in methanol extract, in which 100% ovicidal activity was recorded in C. quinquefasciatus, and 72% ovicidal activity was recorded in A. aegypti at 500 ppm. The hexane extract was found to be the most effective protectant against the adult mosquitoes of both species. The mean protection time recorded in hexane extract was up to 273 and 165 min at 5 mg/cm2 dosage against C. quinquefasciatus and A. aegypti, respectively. Considering these bioactivities, C. celata could be used to obtain some novel pesticidal molecules.

Differential defensive response of groundnut germplasms to Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)

Host plant resistance is one of the most economic and environment friendly method for pest management and, therefore, the present study was undertaken on induction of resistance against Helicoverpa armigera in three groundnut genotypes (ICGV 86699-resistant, NCAc 343-resistant, and TMV 2-susceptible). Observations were recorded on oxidative enzymes [peroxidase (POD) and polyphenol oxidase (PPO)], and on the amounts of other defensive components such as total phenols, hydrogen peroxide (H2O2), malondialdehyde (MDA), and proteins after 24, 48, 72, and 96 h following H. armigera infestation to understand the induced defense to H. armigera. Data were also recorded on leaf damage, larval survival, and larval weights. Increase in activities of POD and PPO and in the amounts of total phenols, H2O2, MDA, and proteins were observed in insect damaged plants as compared to uninfested control plants. In general, the induction was greater in the insect resistant genotypes than in the susceptible one. Leaf damage, larval survival, and larval weight were lower in resistant genotypes as compared to susceptible genotype. Therefore, induced resistance could be exploited in plant defense against insect pests for integrated pest management.