Anil Dahuja

In vitro kinetics of soybean lipoxygenase with combinatorial fatty substrates and its functional significance in off flavour development

Lipoxygenase (Lox) mediated oxidation of polyunsaturated fatty acids (PUFA) in mature soya seeds results in objectionable flavour. In the present study, Lox isozymes were purified to near homogeneity (107-fold). Lox-2 and 3 displayed remarkable kinetic preference (1.7 and 1.5-fold, respectively) for low PUFA ratios (LA/LeA) (PRs) among the selected PUFA combinations. Lox-1 displayed no specific preference. Pure Lox-1 displayed unbiased response towards substrates with marginal preference (1.2-fold) for linoleic acid at its optimum pH. Volatile compounds profiling showed a direct relationship between PRs and hexanal to trans-2-hexenal (1.47, 2.24 and 18.90 for 2, 7 and 15 PRs, respectively) ratio. The off-flavour determining parameters like TBA value, carbonyl value and lipid hydroperoxides (LHPODs) exhibited significant negative correlation (0.76, 0.74, 0.72; p<0.0001) in selected soya genotypes displaying varied PRs and significant positive correlation (0.89, 0.81. 0.89; p<0.0001) with ratio of PI (polyene index) to PRs - suggesting the plausible significance of PUFA ratios in biological lipid peroxidation.

Role of phytosterols in drought stress tolerance in rice

Phytosterols are integral components of the membrane lipid bilayer in plants. They regulate membrane fluidity to influence its properties, functions and structure. An increase in accumulation of phytosterols namely campesterol, stigmasterol and β-sitosterol was observed in rice as seedlings matured. The levels of the major phytosterol, β-sitosterol in N22 (drought tolerant) rice seedlings was found to increase proportionately with severity of drought stress. Its levels were 145, 216, 345 and 364 μg/g FW after subjecting to water stress for 3, 6, 9 and 12 days respectively, while for IR64 (drought susceptible), levels were 137, 198, 227 and 287 μg/g FW at the same stages. Phytosterols were also found to increase with maturity as observed at 30, 50 and 75 days after planting. The activity of HMG-CoA reductase (EC 1.1.1.34) which is considered to be a key limiting enzyme in the biosynthesis of phytosterols was 0.55, 0.56, 0.78 and 0.85 μmol/min/L at 3, 6, 9 and 12 days of water stress in N22 and 0.31, 0.50, 0.54 and 0.65 μmol/min/L in case of IR64 respectively. The elevation in the levels of phytosterols as well as the activity of HMG-CoA reductase during drought stress indicates the role of phytosterols in providing tolerance to stress.

Contemporary Understanding of miRNA-Based Regulation of Secondary Metabolites Biosynthesis in Plants

Plants secondary metabolites such as flavonoids, terpenoids, and alkaloids etc. are known for their role in the defense against various insects-pests of plants and for medicinal benefits in human. Due to the immense biological importance of these phytochemicals, understanding the regulation of their biosynthetic pathway is crucial. In the recent past, advancement in the molecular technologies has enabled us to better understand the proteins, enzymes, genes, etc. involved in the biosynthetic pathway of the secondary metabolites. miRNAs are magical, tiny, non-coding ribonucleotides that function as critical regulators of gene expression in eukaryotes. Despite the accumulated knowledge of the miRNA-mediated regulation of several processes, the involvement of miRNAs in regulating secondary plant product biosynthesis is still poorly understood. Here, we summarize the recent progress made in the area of identification and characterizations of miRNAs involved in regulating the biosynthesis of secondary metabolites in plants and discuss the future perspectives for designing the viable strategies for their targeted manipulation.

RNA Interference: A Novel Source of Resistance to Combat Plant Parasitic Nematodes

Plant parasitic nematodes cause severe damage and yield loss in major crops all over the world. Available control strategies include use of insecticides/nematicides but these have proved detrimental to the environment, while other strategies like crop rotation and resistant cultivars have serious limitations. This scenario provides an opportunity for the utilization of technological advances like RNA interference (RNAi) to engineer resistance against these devastating parasites. First demonstrated in the model free living nematode, Caenorhabtidis elegans; the phenomenon of RNAi has been successfully used to suppress essential genes of plant parasitic nematodes involved in parasitism, nematode development and mRNA metabolism. Synthetic neurotransmitants mixed with dsRNA solutions are used for in vitro RNAi in plant parasitic nematodes with significant success. However, host delivered in planta RNAi has proved to be a pioneering phenomenon to deliver dsRNAs to feeding nematodes and silence the target genes to achieve resistance. Highly enriched genomic databases are exploited to limit off target effects and ensure sequence specific silencing. Technological advances like gene stacking and use of nematode inducible and tissue specific promoters can further enhance the utility of RNAi based transgenics against plant parasitic nematodes.

Paclobutrazol minimises the effects of salt stress in mango (Mangifera indica L.)

Summary We investigated the effects of paclobutrazol (PBZ) on 1-year-old plants of ‘Olour’ mango subjected to NaCl stress under polythene tunnel conditions. Plants were treated with two levels of salt [0.0 g NaCl kg−1 soil (control) or 1 g NaCl kg−1 soil] and three concentrations of paclobutrazol [PBZ; 0.0 mg l−1 (control), 750 mg l−1 or 1,500 mg l−1] after 30 d of establishment. Mortality in saline-treated mango plants was reduced significantly (LSD = 8.55; P ≤ 0.05) following the application of PBZ. NaCl-stress reduced the survival of plants without PBZ treatment by 89%, but only by 28.4% for 1,500 mg l−1 PBZ-treated plants. PBZ-treated plants also showed less defoliation, and fewer leaves per plant exhibited salt stress symptoms. It was also evident that treatment with PBZ increased the relative water and chlorophyll contents of mango seedlings, and reduced membrane injury, under salt stress. Furthermore, saline treatment without PBZ increased the Na+ and Cl− ion contents of leaves and roots; however, application of PBZ consistently and significantly lowered these ion contents (P ≤ 0.05). The Na+ content of leaves on saline-treated plants was reduced by 1.96- to 2.12-fold, whereas Cl− ion contents were reduced by 22 – 39% by PBZ treatment compared to salt-treated seedlings without PBZ. Our results suggest a role for PBZ in promoting the avoidance of salt stress in mango by increasing the levels of photosynthetic pigments, water content, K+ uptake and accumulation, and by reducing defoliation, the membrane injury index, and the uptake and accumulation of harmful Na+ and Cl− ions. These findings may be used to improve the yields and quality of mango trees grown in salt-affected areas.

Biochemical and salt ion uptake responses of seven mango (Mangifera indica L.) rootstocks to NaCl stress

Summary Uniform-sized, 6-month-old seedlings of seven mango (Mangifera indica L.) rootstocks (‘Moovandan’, ‘Bappakai’, ‘Nekkare’, ‘Kurukkan’, ‘Olour’, ‘Terpentine’, and ‘Chandrakaran’) were irrigated with tap water containing 0, 50, 100, or 150 mM NaCl at 4 d intervals for 40 d. NaCl stress increased the activities of peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD), and the concentrations of malondialdehyde (MDA), proline, and trehalose. The highest anti-oxidant enzyme activities were observed in the rootstocks ‘Olour’, ‘Bappakai’ and ‘Terpentine’ at the highest level of salinity (150 mM NaCl). Leaf proline concentrations increased most in ‘Olour’, ‘Kurukkan’, and ‘Terpentine’ with increasing levels of salinity. The concentration of Na+ ions in leaf tissues increased to a maximum (123.5%) of the respective (0 mM NaCl) control in ‘Chandrakaran’, while ‘Bappakai’ had the highest Na+ ion concentration in root tissues at the highest level of salinity (77.3%) compared to the respective control. Compared to the respective controls, the maximum increase (109.1%) in leaf Cl– ion concentration was recorded in ‘Moovandan’, while ‘Chandrakaran’ had the highest concentration of Cl– ions (139.3%) in its root tissues when irrigated with water containing 150 mM NaCl. Our results suggest that the salt-tolerant behaviour of the mango rootstocks ‘Olour’ and ‘Terpentine’ may be due to their ability to inhibit the uptake of Cl– and Na+ ions, combined with higher accumulations of proline.These two rootstocks may therefore be used to improve the yield and quality of commercial mango cultivars grown in salt-affected areas.

EFFECT OF PACLOBUTRAZOL AND PUTRESCINE ON ANTIOXIDANT ENZYMES ACTIVITY AND NUTRIENTS CONTENT IN SALT TOLERANT CITRUS ROOTSTOCK SOUR ORANGE UNDER SODIUM CHLORIDE STRESS

The effects of paclobutrazol (PBZ) and putrescine (Put) on antioxidant enzymes activity, proline contents and nutrients uptake were studied on salt tolerant citrus rootstock sour orange. Six-month-old nucellar seedlings grown in pots and subjected to three levels of PBZ and two levels each of salinity and Put for 90 days. Seedlings treated with PBZ or Put alone or in combination had higher anti-oxidant enzymes activities, accumulation of proline and nutrients contents like potassium (K+) and calcium (Ca2+) under both saline and non-saline conditions. Further, application of PBZ or Put alone or in combination also reduced the accumulation of both Na+ and Cl− ions in leaves and roots in NaCl stressed seedlings. A combined application of 250 mg L−1 PBZ and 50 mg L−1 Put proved to be more effective in improving proline and Ca2+ content and restricting accumulation of Na+ ions in leaf tissues.

Enhanced nutraceutical potential of gamma irradiated black soybean extracts.

Radiation processing of soybean, varying in seed coat colour, was carried out at dose levels of 0.25, 0.5 and 1 kGy to evaluate their potential anti-proliferative and cytoprotective effects in an in vitro cell culture system. Irradiated and control black (Kalitur) and yellow (DS9712) soybean extracts were characterized in terms of total phenolics, flavonoids and anthocyanins, especially cyanidin-3-glucoside (C3G). Using an epithelial cell line, BEAS-2B the potential cytoprotective effects of soybean extracts were evaluated in terms of intracellular ROS levels and cell viability. The most relevant scavenging effect was found in Kalitur, with 78% decrease in ROS, which well correlated with a 33% increase in C3G after a 1 kGy dose. Results evidenced a correspondence between in vitro antioxidant activity and a potential health property of black soybean extracts, exemplifying the nutraceutical role of C3G. To our knowledge this study is the first report validating the cytoprotective effects of irradiated black soybean extracts.

Effect of NaCl in the irrigation water on growth, anti-oxidant enzyme activities, and nutrient uptake in five citrus rootstocks

Summary Seven–month-old, uniform-sized seedlings of five citrus rootstocks [sour orange (Citrus aurantiam), Attani-2 (C. rugulosa), Troyer citrange (C. sinensis × Poncirus trifoliata), billikhichlli (C. reshni), and RLC-6 (C. jambhiri)] were irrigated to 70% of field capacity with water containing 0, 50, 100, or 200 mM NaCl for 180 d. Growth, in terms of plant heights and the numbers of leaves, decreased with increasing levels of salinity in all five rootstocks. The decrease in plant height was greatest in the salt-susceptible Troyer citrange and billikhichlli at higher levels of salinity. However, in the salt-tolerant sour orange and Attani-2, NaCl caused only a slight decrease in plant height. Defoliation was maximum in the salt-susceptible Troyer citrange and billikhichlli. The maximum increases in superoxide dismutase (SOD) and peroxidase (POD) activities were found in the salt-susceptible Troyer citrange at higher levels of salinity. Leaf proline contents increased most in Attani-2, sour orange, and RLC-6 at higher levels of salinity.The concentration of Na+ ions in leaf tissues increased to a maximum in Attani-2; while, in root tissues, RLC-6 and Troyer had the highest Na+ ion contents. The maximum increase in leaf Cl– ion levels occurred in Troyer citrange, and the minimum was in RLC-6, at 200 mM NaCl. These data suggest that higher levels of proline accumulation and leaf abscission could be used as indicators for screening citrus rootstocks for resistance to NaCl stress. Sour orange and Attani-2 were able to exclude Cl– ions, whereas Troyer citrange appeared to exclude Na+ ions at lower levels of NaCl. Further studies are required to observe the translocation of harmful and beneficial mineral elements to scion cultivars grafted onto sour orange and Attani-2 and grown under NaCl stress. Overall, salt-tolerance increased in the following order: Troyer ì billikhichlli ì RLC-6 ì Attani-2 ì sour orange.

Salinity induced changes in the chloroplast proteome of the aquatic pteridophyte Azolla microphylla

The growth of the nitrogen fixing aquatic pteridophyte Azolla microphylla is severely affected by salinity. Salinity exposure (0.5%) resulted in significant reduction in chlorophyll a and b content, altered chl a/b ratio and photosynthetic efficiency (Fv/Fm). Chloroplasts maintain photosynthesis but are highly sensitive to salinity stress. Chloroplast proteins extracted from A. microphylla was separated by two-dimensional electrophoresis (2DE) and approximately 200 proteins were observed on each gel. Forty two differentially expressed protein spots were detected and out of this 17 could be identified through MALDI-TOF-MS/MS analysis. Out of the 17 identified proteins, 15 were found to be down regulated and 2 proteins were up regulated. Most of the down regulated proteins were associated with Calvin cycle, ATP synthesis, oxygen evolution, photosystem I and ROS scavenging. The results show changes in proteome dynamics of the chloroplasts of A. microphylla and such changes may lead to reduction in growth and metabolism. The primary target of salinity in A. microphylla is photosynthesis and the changes in the proteome dynamics of the chloroplasts lead to reduced growth.