T. Shivanandappa

Botanicals as Grain Protectants

Prevention of food losses during postharvest storage is of paramount economic importance. Integrated pest management is now a widely accepted strategy in pest control including postharvest infestation control which involves the use of chemical (contact/residual) insecticides along with fumigants. The use of synthetic chemical insecticides is either not permitted or used restrictively because of the residue problem and health risks to consumers. In view of the above, there is a need for plants that may provide potential alternatives to the currently used insect control agents as they constitute a rich source of bioactive molecules. Available literature indicates that plant could be source for new insecticides. Therefore, there is a great potential for a plant-derived insecticidal compounds. This paper focuses on the current state of the botanical insecticides as grain protectants and its mode of action.

Brain aging, memory impairment and oxidative stress: A study in Drosophila melanogaster

Memory impairment during aging is believed to be a consequence of decline in neuronal function and increase in neurodegeneration. Accumulation of oxidative damage and reduction of antioxidant defense system play a key role in organismal aging and functional senescence. In our study, we examined the age-related memory impairment (AMI) in relation to oxidative stress using Drosophila model. We observed a decline in cognitive function in old flies with respect to both short-lived and consolidated forms of olfactory memory. Light and electron microscopy of mushroom bodies revealed a reduction in the number of synapses and discernible architectural defects in mitochondria. An increase in neuronal apoptosis in Kenyon cells was also evident in aged flies. Biochemical investigations revealed a comparable age-associated decrease in the activity of antioxidant enzymes such as catalase and superoxide dismutase as well as the GSH level, accompanied by an increase in the level of lipid peroxidation and generation of reactive oxygen species in the brain. There was no significant difference in the activity level of AChE and BChE enzymes between different age groups while immunohistochemical studies showed a significant decrease in the level of ChAT in 50-day-old flies. RNAi-mediated silencing of cat and sod1 genes caused severe memory impairment in 15-day-old flies, whereas, over-expression of cat gene could partially rescue the memory loss in the old flies. We demonstrated that a Drosophila long-lived strain, possessing enhanced activity of antioxidant enzymes and higher rate of resistance to oxidative stress, shows lower extent of AMI compared to normal lifespan strain. Present study provides evidence for involvement of oxidative stress in AMI in Drosophila.

ATTENUATION OF NEUROMOTOR DEFICITS BY NATURAL ANTIOXIDANTS OF DECALEPIS HAMILTONII IN TRANSGENIC DROSOPHILA MODEL OF PARKINSON'S DISEASE

Oxidative stress is believed to be a major factor for the onset of Parkinsons disease (PD). In this study, we have investigated oxidative status in transgenic Drosophila model of PD. Our results revealed elevated levels of reactive oxygen species (ROS) and lipid peroxidation (LPO) in A30P and A53T α-synuclein PD model flies compared to control. We have demonstrated for the first time the ameliorating potential of natural antioxidants characterized from the roots of Dh in A30P and A53T α-synuclein PD model flies. Feeding of transgenic flies with aqueous Dh root extract for 21 days significantly improved their climbing ability and circadian rhythm of locomotor activity which was associated with reduction in levels of ROS and LPO and enhancement in the activities of catalase (CAT) and superoxide dismutase (SOD). Dh protected against paraquat (PQ) sensitivity in α-synuclein transgenic flies and delayed the onset of PD-like symptoms which appears to be mediated by suppression of oxidative stress.

Decalepis hamiltonii root extract attenuates the age-related decline in the cognitive function in Drosophila melanogaster.

Age-associated accumulation of oxidative damage linked to decline of antioxidant defense mechanism, leads to impairment of cognitive function in many organisms. These damages can pass through generations and affect the cognitive quality of progenies. In Drosophila, classical olfactory conditioning results in the formation of different types of memory. Age-related memory impairment (AMI) causes reduction in middle term memory (MTM) and parental senescence causes decline in short-term memory (STM) of the offspring. We have further examined the neuromodulatory effect of Decalepis hamiltonii (Dh) root extract, which is a cocktail of novel antioxidant molecules, on the biochemical oxidative defenses in relation to cognitive ability of the aged flies and their offspring. There is a strong correlation between the age-related decline in the activity of the antioxidant enzymes and the lower cognitive ability of the aged flies and their offspring. Feeding of aged flies in the diet containing 0.1% Dh, markedly enhances the cognitive ability of both aged flies and their offspring which is associated with enhanced antioxidant defenses as evident for the activity of superoxide dismutase (SOD) and catalase. Our findings, for the first time, show that the antioxidant-rich Dh root extract attenuates the age-related decline in cognitive ability of Drosophila, and also shows ameliorative effect on the memory of the offspring.

Modulatory effect of Decalepis hamiltonii on ethanol-induced toxicity in transgenic Drosophila model of Parkinson's disease

Overexpression of human α-synuclein gene in Drosophila can reduce lifespan, and we have performed lifespan assay for A30P and A53Tα-synuclein transgenic and control (elav-GAL4, UAS-A30P, UAS-A53T) flies. Our results showed reduced lifespan of transgenic flies compared to controls. We have also investigated behavioral responses, levels of reactive oxygen species (ROS) and lipid peroxidation (LPO) and activities of catalase (CAT) and superoxide dismutase (SOD) in a combined genetic-toxin model (Ethanol-A30P or A53Tα-synuclein models) and controls. Our results showed that sedation time (ST50) of A30P or A53Tα-synuclein PD model flies was significantly lower while recovery time (RC50) of them was remarkably higher compared to control flies. The levels of oxidative markers (ROS and LPO) were significantly higher and the activities of CAT and SOD were lower in transgenic flies that underwent ethanol exposure compared to control. Based on our earlier studies on antioxidant properties of isolated and characterized molecules from Decalepis hamiltonii (Dh) root extract, its protective effect in this combined toxicity model has been investigated. Surprisingly, Dh treatment increased ST50 and decreased RC50 values of transgenic flies. Moreover, we showed that Dh pre-treatment could decrease the levels of ROS and LPO and increase the activities of CAT and SOD in the ethanol-α-synuclein model. This is the first report on protective effects of natural antioxidants in A30P or A53Tα-synuclein PD model flies against oxidative stress induced by ethanol.

Mode of Action of Plant-Derived Natural Insecticides

Most of the chemical insecticides are neurotoxic, acting on targets in the central nervous system such as the membrane ion channels (DDT, pyrethroids), the enzyme acetylcholinesterase (organophosphate, carbamate), and the receptors of neurotransmitters (avermectins, neonicotinoids). The recently introduced diamide group of insecticides target the novel ryanodine receptor in the nervous system. Since pests continue to evolve resistance to compounds currently in use, new compounds with new modes of action are needed. Natural products could be a promising source for novel pest control agents. The origin of many of the important insecticide classes is traceable to a natural source as in the case of pyrethroids, avermectins, spinosads, and neonicotinoids. Although insect control agents acting on targets other than the nervous system such as insect growth regulators (e.g., azadirachtin, JH analogues, ecdysone antagonists) have been developed, due to their lack of contact toxicity, they are not quite successful, but find a place in the integrated pest management. Recent progress in understanding the biology of insect olfaction and taste offers new strategies for developing selective pest control agents. Decalesides, recently discovered natural insecticides, represent a new class of plant-derived insecticides targeting the tarsal gustatory receptors. In this chapter, we focus on the toxicity and mode of action of natural insecticides.

Sex differences in oxidative stress resistance in relation to longevity in Drosophila melanogaster

Gender differences in lifespan and aging are known across species. Sex differences in longevity within a species can be useful to understand sex-specific aging. Drosophila melanogaster is a good model to study the problem of sex differences in longevity since females are longer lived than males. There is evidence that stress resistance influences longevity. The objective of this study was to investigate if there is a relationship between sex differences in longevity and oxidative stress resistance in D. melanogaster. We observed a progressive age-dependent decrease in the activity of SOD and catalase, major antioxidant enzymes involved in defense mechanisms against oxidative stress in parallel to the increased ROS levels over time. Longer-lived females showed lower ROS levels and higher antioxidant enzymes than males as a function of age. Using ethanol as a stressor, we have shown differential susceptibility of the sexes to ethanol wherein females exhibited higher resistance to ethanol-induced mortality and locomotor behavior compared to males. Our results show strong correlation between sex differences in oxidative stress resistance, antioxidant defenses and longevity. The study suggests that higher antioxidant defenses in females may confer resistance to oxidative stress, which could be a factor that influences sex-specific aging in D. melanogaster.

Is Longevity a Heritable Trait? Evidence for Non-genomic Influence from an Extended Longevity Phenotype of Drosophila melanogaster

BACKGROUND Although genetic variations are heritable, some quantitative traits like longevity may have non-genomic influence on heritability. Laboratory-selected inbred strains of extended longevity phenotype of Drosophila offer an opportunity to study the inheritance of longevity. OBJECTIVE The aim of the study was to examine the heritability of longevity in an extended longevity phenotype of Drosophila melanogaster using reciprocal cross effects in F1 and F2 generations. METHODS Lifespan variations of virgin and mated flies in parent, F1 and F2 generations were investigated using reciprocal crosses between normal and long lifespan lines of inbred population of D. melanogaster. Heterosis, narrow-sense heritability, recombination loss, maternal effect and overdominance with respect to survivorship in virgin and mated flies were analyzed. RESULTS Virgin flies lived longer than mated flies. There was no significant effect of mid-parent heterosis, recombination loss and overdominance on variations in longevity, whereas, significant maternal effect and narrow-sense heritability were observed in mated and virgin flies, respectively. CONCLUSION Absence of heterosis in our study population of Drosophila phenotypes could be due to the lack of genetic heterogeneity. The heritability of the longevity trait in an inbred extended longevity phenotype depends on the variations in genetic and environmental factors.

Life history traits of an extended longevity phenotype of Drosophila melanogaster

BACKGROUND Aging or senescence is a complex biological phenomenon. Artificially selected Drosophila for extended longevity is one of the experimental models used to understand the mechanisms involved in aging and to test various theories. OBJECTIVE To examine the life history traits and biochemical defenses in relation to aging in an extended longevity phenotype of Drosophila melanogaster. METHODS Life history traits viz., survivability, fecundity, development time, dry weight, wing size, lipid content, starvation, desiccation and cold resistances, locomotory ability, antioxidant enzyme activities and reactive oxygen species level between control and selected lines of D. melanogaster were investigated. RESULTS In our model of Drosophila, extended longevity is associated with no trade-off in fecundity and shows variable resistance to environmental stress such as starvation, cold and desiccation. Enhanced biochemical defense involving the antioxidant enzymes was positively correlated with longevity. CONCLUSION Extended longevity phenotypes of Drosophila represent genomic plasticity associated with variable life history traits attributed to the genetic background of the progenitor population and the environment of selection. Oxidative stress resistance seems to be a significant factor in longevity.

Radioprotective potential of Decalepis hamiltonii: A study on gamma radiation-induced oxidative stress and toxicity in Drosophila melanogaster

Radiation-induced damage to normal tissues restricts the therapeutic use of radiation in clinical application for cancer treatment and thereby limits the efficacy of the treatment. The use of chemical compounds as radioprotectors is a desirable strategy to improve the therapeutic index of radiotherapy. However, most of the synthetic radioprotective compounds studied have shown to have undesirable properties of toxicity. There is a need for safer, natural radioprotective agents without compromising efficacy of the treatment. We have investigated the radioprotective potential of Decalepis hamiltonii (Dh) root extract which is rich in natural antioxidants by employing Drosophila melanogaster as a model. Irradiation of Drosophila with 100, 200, and 400 Gy of gamma radiation induced dose-dependent mortality. Elevation in the levels of thiobarbituric acid reactive substances (TBARS), the activities of catalase (CAT) and superoxide dismutase (SOD), and depletion of glutathione (GSH) content suggested radiation-induced oxidative stress. Pretreatment of flies with Dh root extract protected them from radiation-induced mortality and oxidative stress as evidenced by reduction in TBARS and restoration of the antioxidant enzymes, SOD and CAT, and GSH to control levels. This is the first report of radioprotective action of Dh root extract in D. melanogaster.