Asok K. Biswas

Regulation of growth and metabolism in rice (Oryza sativa L.) by arsenic and its possible reversal by phosphate

Abstract The effect of arsenate with or without phosphate on the growth and metabolism in rice seedlings cv. MTU1010 was studied. In the test, cv. arsenic was more toxic for root growth, than for shoot growth, where root hairs were fewer and short, roots were characteristically stubby, brittle and root tips gradually turned brown. Arsenic caused damage to the root epidermal cells and aerenchymatous cortex. The level of total chlorophyll, chlorophyll-a, chlorophyll-b and fluorescence intensity were decreased in arsenic treated rice seedlings. Arsenic toxicity affected the activities of different antioxidant scavenging enzymes in the test seedlings. Activities of superoxide dismutase and ascorbic acid oxidase were increased, whereas catalase and catechol peroxidase activities were decreased by arsenic application. In these seedlings, the oxidative stress has been observed with arsenic treatments and the level of proline, H2O2 and malondialdehyde contents were increased. Joint application of phosphate with arsenic showed significant alterations on all parameters tested under the purview of arsenic treatment alone leading to better growth and metabolism in rice seedlings. Thus the use of phosphorus enriched fertilizers in arsenic contaminated soil may improve the production of healthy rice plants.

Regulation of sugar metabolism in rice (Oryza sativa L.) seedlings under arsenate toxicity and its improvement by phosphate.

The effect of arsenate with or without phosphate on the growth and sugar metabolism in rice seedlings cv. MTU 1010 was studied. Arsenate was found to be more toxic for root growth than shoot growth and water content of the seedlings gradually decreased with increasing concentrations. Arsenate exposure at 20 μM and 100 μM resulted in an increase in reducing sugar content and decrease in non-reducing sugar content. There was a small increase in starch content, the activity of starch phosphorylase was increased but α-amylase activity was found to be decreased. Arsenate toxicity also affected the activities of different carbohydrate metabolizing enzymes. The activities of sucrose degrading enzymes viz., acid invertase and sucrose synthase were increased whereas, the activity of sucrose synthesizing enzyme, viz. sucrose phosphate synthase declined. The combined application of arsenate with phosphate exhibited significant alterations of all the parameters tested under the purview of arsenate treatment alone which was congenial to better growth and efficient sugar metabolism in rice seedlings. Thus, the use of phosphorus enriched fertilizers may serve to ensure the production of healthy rice plants in arsenic contaminated soils.

Interactive influence of arsenate and selenate on growth and nitrogen metabolism in wheat (Triticum aestivum L.) seedlings

The effect of arsenate and selenate, either alone or in combination, on plant growth and nitrogen metabolism was studied in wheat seedlings. The root-shoot elongation and the biomass production were significantly decreased with increasing arsenate concentrations. Arsenate toxicity severely affected activities of different antioxidant scavenging enzymes and oxidative stress markers in the test seedlings. The activities of nitrate and nitrite reductase were also affected resulting in reduced nitrate and nitrite contents. Glutamine synthetase and glutamate synthase activities were also reduced, whereas the glutamate dehydrogenase activity was substantially increased resulting in an increased accumulation of ammonium contents in the test seedlings. Arsenate treatments also adversely affected the levels of total and soluble nitrogen contents and free amino acid contents. Combined application of arsenate with selenate in the test seedlings showed significant alterations in all parameters tested under the purview of arsenate treatment alone leading to better growth and nitrogen metabolism.

Arsenic-induced oxidative stress and thiol metabolism in two cultivars of rice and its possible reversal by phosphate

Groundwater arsenic contamination, a grave threat in Bangladesh and parts of West Bengal (India), causes biochemical and physiological disorders in plants. Arsenic and phosphorus (plant macronutrient) have similar electronic configurations, resulting in their competitive interaction for the same uptake system in plant roots. Arsenic exposure initiates production of reactive oxygen species. Hence, the contents of proline, hydrogen peroxide, glutathione, ascorbate, and activities of ascorbate peroxidase, catalase were investigated in 21-day-old rice seedlings (cv. Khitish and cv. Nayanmani). Additionally, impact of arsenate together with phosphate on growth, total glutathione contents and activity of its regulatory enzymes were altered in the test cultivars to varying extents. Inductively coupled plasma-optical emission spectroscopic study of arsenic content in the root and shoot also showed variable uptake of arsenic by the two cultivars. Arsenate reductase enzyme activity primarily observed in the root, also differed from one cultivar to the other. Different phytochelatin (PCs) levels were recorded in the shoot and root of the cultivars under arsenate and phosphate treatment by reverse phase-high performance liquid chromatography. PC content increased with increasing arsenate concentrations, whereas phosphate and arsenate co-application resulted in reduced PC levels. The degree of elevation in PC contents varied significantly in the cultivars. Based on the above-mentioned parameters, cv. Khitish appeared to be more susceptible to arsenic toxicity than cv. Nayanmani which showed selective tolerance to the said metal stress.

Metabolomics analysis of Cajanus cajan L. seedlings unravelled amelioration of stress induced responses to salinity after halopriming of seeds

ABSTRACT Soil salinity has become a major concern for agriculture. Such constraints not only reinforce the urgent need to understand the underlying mechanisms by which plants cope during salt stress but also to develop cost-effective and farmer friendly halopriming technique to alleviate the adverse effects of salinity to some extent. Metabolomics approach was used to explore different responses to physiological metabolites and pathway variations that occur during salt stress responses in Cajanus cajan L. var. Rabi and to understand the role of halopriming in ameliorating stress at the level of metabolite. Seedlings raised from non-primed and haloprimed seeds, grown in hydroponic solution, were subjected to different concentrations of NaCl. After 21 days, metabolites were extracted, derivatized and analyzed by GC-MS. The data were analysed by different multivariate analyses. Chemometric study of the identified metabolites indicated that the leaves responded most to NaCl induced stress than the stem and root with production of beta-cyano-L-alanine and also increased level of different compatible solutes. O-Acetylsalicylic was also found to increase in all the parts upon facing stress but, such upregulated metabolite production was downregulated in the leaves when the seeds were haloprimed before germination, although many of the metabolites, including beta-cyanoalanine, showed a trend of increase with increase in salt concentrations. Important metabolites produced by C. cajan seedlings in response to salinity were unravelled. Pre-germination haloprimimg of seeds resulted in amelioration of NaCl induced stress, as the levels of stress induced metabolites were lowered.