Tapas Kumar Roy

Computational reverse chemical ecology: virtual screening and predicting behaviorally active semiochemicals for Bactrocera dorsalis.

BackgroundSemiochemical is a generic term used for a chemical substance that influences the behaviour of an organism. It is a common term used in the field of chemical ecology to encompass pheromones, allomones, kairomones, attractants and repellents. Insects have mastered the art of using semiochemicals as communication signals and rely on them to find mates, host or habitat. This dependency of insects on semiochemicals has allowed chemical ecologists to develop environment friendly pest management strategies. However, discovering semiochemicals is a laborious process that involves a plethora of behavioural and analytical techniques, making it expansively time consuming. Recently, reverse chemical ecology approach using odorant binding proteins (OBPs) as target for elucidating behaviourally active compounds is gaining eminence. In this scenario, we describe a “computational reverse chemical ecology” approach for rapid screening of potential semiochemicals.ResultsWe illustrate the high prediction accuracy of our computational method. We screened 25 semiochemicals for their binding potential to a GOBP of B. dorsalis using molecular docking (in silico) and molecular dynamics. Parallely, compounds were subjected to fluorescent quenching assays (Experimental). The correlation between in silico and experimental data were significant (r2 = 0.9408; P < 0.0001). Further, predicted compounds were subjected to behavioral bioassays and were found to be highly attractive to insects.ConclusionsThe present study provides a unique methodology for rapid screening and predicting behaviorally active semiochemicals. This methodology may be developed as a viable approach for prospecting active semiochemicals for pest control, which otherwise is a laborious process.

Role of oxidative stress and the activity of ethylene biosynthetic enzymes on the formation of spongy tissue in 'Alphonso' mango.

Spongy tissue formation in ‘Alphonso’ mangoes (Mangifera indica L) is a major national problem leading to loss for farmers and traders. Spongy tissue is whitish sponge like tissue formed near the seed with insipid taste and off odour. Lipid peroxidation of membranes as studied by malondialdehyde formation was significantly higher in spongy tissue. Activities of antioxidative enzymes like superoxide dismutase, catalase, peroxidase and polyphenol oxidase were lower in spongy tissue. Among the antioxidative enzymes, activities of catalase and peroxidases were severely reduced leading to membrane damage in spongy tissue. A significant reduction in 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase and accumulation of ACC was also observed in spongy tissue. However, ACC synthase activity in spongy tissue was more compared to healthy tissue. Results indicate that the membrane peroxidation leading to lower activity of ACC oxidase might lead to the formation of spongy tissue in ‘Alphonso’ mango.

Improvement in shelf life of minimally processed cilantro leaves through integration of kinetin pretreatment and packaging interventions: Studies on microbial population dynamics, biochemical characteristics and flavour retention

Effect of integrating optimized combination of pretreatment with packaging on shelf life of minimally processed cilantro leaves (MPCL) was appraised through analysis of their sensory attributes, biochemical characteristics, microbial population and flavour profile during storage. Minimally pretreated cilantro leaves pretreated with 50ppm kinetin and packed in 25μ polypropylene bags showed a shelf life of 21days. Optimized combination helped in efficiently maintaining sensory parameters, flavour profile, and retention of antioxidants in MPCL until 21days. Studies conducted on the effect of optimized combination on microbial population and flavour profile revealed that among different microorganisms, pectinolysers had a significant effect on spoilage of MPCL and their population of ⩽3.59logcfu/g was found to be acceptable. Principal component analysis of headspace volatiles revealed that (E)-2-undecenal, (E)-2-hexadecenal, (E)-2-tetradecenal & (E)-2-tetradecen-1-ol in stored samples clustered with fresh samples and therefore, could be considered as freshness indicators for MPCL.

Do seed VLCFAs trigger spongy tissue formation in Alphonso mango by inducing germination

Spongy tissue is a physiological disorder in Alphonso mango caused by the inception of germination-associated events during fruit maturation on the tree, rendering the fruit inedible. Inter-fruit competition during active fruit growth is a major contributing factor for the disorder which leads to reduced fat content in spongy tissue affected fruits. This study was, therefore, carried out to determine the possible association between seed fats and ST formation. The study of the fat content during fruit growth showed that it increased gradually from 40% fruit maturity. At 70% maturity, however, there was a sudden increase of fat content of whole fruit, leading to acute competition and resulting in differential allocation of resources among developing fruits. As a result, the seed in spongy-tissue-affected mature ripe fruit showed a marked drop in the levels of fats and the two very long chain fatty acids (VLCFAs), tetracosanoic acid and hexacosanoic acid together with an increase of linolenic acid and a fall in oleic acid contents, which are known to be key determinants for the initiation of pre-germination events in seed. Subsequently, a rise in the level of cytokinin and gibberellins in ST seed associated with a fall in abscisic acid level clearly signalled the onset of germination. Concurrently, a significant reduction in the ratio of linolenic acid/linoleic acid in pulp led to the loss of membrane integrity, cell death and the eventual formation of spongy tissue. Based on the above, it is concluded that a significant reduction in the biosynthesis of VLCFAs in seeds during fruit growth might trigger pre-germination events followed by a cascade of biochemical changes in the pulp, leading to lipid peroxidation and membrane injury in pulp culminating in ST development. Thus, this study presents crucial experimental evidence to highlight the critical role played by VLCFAs in inducing ST formation in Alphonso mango during the pre-harvest phase of fruit growth.

Barrier against water loss: relationship between epicuticular wax composition, gene expression and leaf water retention capacity in banana

In the present study we examined 13 banana (Musa spp.) genotypes belonging to different genomic groups with respect to total leaf cuticular wax concentration, chemical composition, carbon chain length and their relationship with leaf water retention capacity (LWRC). A positive correlation between epicuticular wax content and LWRC clearly indicated that the cuticular wax plays an important role in maintaining banana leaf water content. The classification of hexane soluble cuticular wax components into different classes based on functional group and their association with LWRC showed that alcohol and ester compounds have a positive correlation. Further, the compounds with >C28 carbon chain length had a positive correlation with LWRC, indicating the role of longer carbon chain length in maintaining the water status of banana leaves. Also, the gene expression analysis showed higher expression of the wax biosynthetic genes FATB and KCS11 in higher wax load genotypes whereas lower expression was seen in low wax banana genotypes. Here, we report for the first time the compositional variations of cuticular wax in different banana genotypes, followed by their association with leaf water retention capacity. The results were also supported by variation in gene expression analysis of cuticular wax biosynthetic genes - FATB and KCS11.

Salicylic Acid Induces Changes in Mango Fruit that Affect Oviposition Behavior and Development of the Oriental Fruit Fly, Bactrocera dorsalis.

The Oriental fruit fly, Bactrocera dorsalis (Hendel) is an important quarantine pest around the globe. Although measures for its control are implemented worldwide through IPM and male annihilation, there is little effect on their population. Hence, there is a need for new strategies to control this minacious pest. A strategy that has received negligible attention is the induction of ‘natural plant defenses’ by phytohormones. In this study, we investigated the effect of salicylic acid (SA) treatment of mango fruit (cv. Totapuri) on oviposition and larval development of B. dorsalis. In oviposition choice assays, gravid females laid significantly less eggs in SA treated compared to untreated fruit. Headspace volatiles collected from SA treated fruit were less attractive to gravid females compared to volatiles from untreated fruit. GC-MS analysis of the headspace volatiles from SA treated and untreated fruit showed noticeable changes in their chemical compositions. Cis-ocimene and 3-carene (attractants to B. dorsalis) were reduced in the headspace volatiles of treated fruit. Further, reduced pupae formation and adult emergence was observed in treated fruit compared to control. Increased phenol and flavonoid content was recorded in treated fruit. We also observed differential expression of anti-oxidative enzymes namely catalase (CAT), polyphenoloxidase (PPO) and peroxidase (POD). In summary, the results indicate that SA treatment reduced oviposition, larval development and adult emergence of B. dorsalis and suggest a role of SA in enhancing mango tolerance to B. dorsalis.

Profiling of anthocyanins and carotenoids in fruit peel of different colored mango cultivars

Mango cultivars are broadly categorized into green, yellow, and red types based on their peel colors. Anthocyanins and carotenoids are the most important pigments responsible for the color of fruits. The information available on the composition of pigments on mango peel was scanty, and the exact role of anthocyanins and carotenoids in imparting peel color was not clear. The present study was aimed at profiling anthocyanin and carotenoid pigments in the peels of green (‘Langra’, ‘Amrapali’, ‘Hamlet’ and ‘Bombay No. 1’), yellow (‘Arka Anmol’, ‘Lazzat Baksh’, ‘Peach’ and ‘Banganapalli’) and red (‘Tommy Atkins’, ‘Lalmuni’, ‘Gulabi’ and ‘Janardhan Pasand’) colored mango cultivars through liquid chromatography and mass spectrometry at different stages of ripening. The analysis helped in the identification of eight carotenoids and 24 anthocyanins in mango peel. Higher levels of carotenoids were observed in yellow colored cultivars, and major compounds were β-carotene and violaxanthin. Further, the red colored types were found to possess the higher anthocyanin content than green and yellow types. The major groups of anthocyanin compounds include cyanidin, peonidin, petunidin, delphinidin and pelargonidin. During fruit ripening, a significant increase in carotenoids content, and no or marginal rise in anthocyanin content was observed in mango peels. The results, show the status of carotenoids and anthocyanins in mango peel of different colored cultivars and their developmental pattern during ripening.

Morphological diversity of trichomes and phytochemicals in wild and cultivated eggplant species

An attempt was made to understand the diversity of trichomes both at morphological and chemical levels in wild (Solanum viarum, S. mammosum, S. indicum, S. gilo, S. torvum) and cultivated eggplant (S. melongena) species. Cultivated and wild eggplant species have morphologically and chemically diverse trichomes. The presence of specific type of trichomes, their densities and chemical composition varied across species. The wild species viz., S. viarum and S. mammosum have seven (Type II to VIII) morphologically distinguishable types of trichomes including two types of glandular trichomes (Type VI, VII) as against uniform occurrence of branched stellate trichomes (Type VIII) alone in cultivated species. Differences among the phytochemicals viz., phenols and flavonoid levels were also observed across the eggplant species and type of trichomes.