Evaluation of changes in lipid peroxidation, ROS production, surface structures, secondary metabolites and yield of linseed (Linum usitatissimum L.) under individual and combined stress of ultraviolet-B and ozone using open top chambers.

The individual and interactive effects of supplemental UV-B (sUV-B) (ambient + 7.2 kJ m-2 d-1) and elevated O3 (ambient + 10 ppb) were evaluated under field conditions using open top chambers on two cultivars, Padmini and T-397 of linseed (Linum usitatissimum L.). Mean monthly surface level of O3 concentrations varied from 27.7 ppb to 59.0 ppb during the experimental period. Both UV-B and O3 induced the production of ROS (H2O2 and O2.-), resulting in significant damage of membranes due to lipid peroxidation and electrolyte leakage. Synthesis of secondary metabolites (flavonoids, anthocyanin, lignin and wax) was also enhanced in all the treatments, whereas biomass and yield were reduced. Alterations in frequency of stomata and wax distribution were also observed through scanning electron microscopy (SEM). Cultivar Padmini was found to be more sensitive because of higher damage of membrane vis-a-vis reduction in biomass and seed yield. However, concentrations of flavonoids, anthocyanin, lignin and wax were higher in T-397, suggesting its relative resistance against applied stress. Combined exposure of sUV-B and O3 was less harmful, as compared to their individual treatment. Among the three treatments, O3 was found to be more detrimental for overall growth and sUV-B for economic yield.

Assessment of litter degradation in medicinal plants subjected to ultraviolet-B radiation.

Litter decomposition is an important component of global carbon budget. Elevated influx of ultraviolet-B radiation (UV-B) as a consequence of depletion of stratospheric ozone (O3) layer may affect litter decomposition directly or/ modifying the plant tissue quality. Chemical composition of plant can affect litter decomposition. In the present study, three important medicinal plant species i.e. Acorus calamus, Ocimum sanctum and Cymbopogon citratus were exposed to two levels of supplemental UV-B (sUV1 and sUV2) during the growth period and examined the changes in leaf quality and degradation of leaf litters. The sUV2 treatment (+3.6 kJ m-2 d-1) increased the rate of decomposition by 45% and 31% respectively; in leaf litters from O. sanctum and C. citratus, while no significant effect was noticed in A. calamus leaf litter. Higher accumulation of sclerenchymatous tissue around vascular bundles and increased concentrations of total phenols by 39 mg g-1 probably lowered the decomposition rate; finding k value: 0.0049 g g-1 d-1 in leaf litters of A. calamus. The C/ N ratio was increased by 14% at sUV2 in C. citratus, whereas in O. sanctum it decreased by 13.6% after treatment. Results of the present experiment illustrates that firstly UV-B can modify the decomposition rate of leaf litter of test plant species, secondly it can alter the tissue chemistry particularly leaf phenolics, N and P concentrations strongly and thus affecting the decay rate and thirdly UV-B effects on decay rate and leaf chemistry is species specific.

Individual and interactive effects of elevated carbon dioxide and ozone on tropical wheat (Triticum aestivum L.) cultivars with special emphasis on ROS generation and activation of antioxidant defence system.

The effects of elevated CO2 and O3, singly and in combination were investigated on various physiological, biochemical and yield parameters of two locally grown wheat (Triticum aestivum L.) cultivars (HUW-37 and K-9107) in open top chambers (OTCs). Elevated CO2 stimulated photosynthetic rate (Ps) and Fv/Fm ratio and reduced the stomatal conductance (gs). Reactive oxygen species, lipid peroxidation, anti-oxidative enzymes, ascorbic acid and total phenolics were higher, whereas Ps, gs, Fv/Fm, protein and photosynthetic pigments were reduced in elevated O3 exposure, as compared to their controls. Under elevated CO2 + O3, elevated levels of CO2 modified the plant performance against O3 in both the cultivars. Elevated CO2 caused significant increase in economic yield. Exposure to elevated O3 caused significant reduction in yield and the effect was cultivar-specific. The study concluded that elevated CO2 ameliorated the negative impact of elevated O3 and cultivar HUW-37 was more sensitive to elevated O3 than K-9107.

Supplemental UV-B radiation induced changes in growth, pigments and antioxidant pool of bean (Dolichos lablab) under field conditions.

Present study is conducted to evaluate the response of bean (Dolichos lablab cv . pusa early prolific) plants to supplemental UV-B (sUV-B: 280-315 nm: 7.2 kJ m-2 d-1) radiation. UV-B caused alteration in biomass translocation pattern with more retention of biomass in below ground parts leading to an increment in root shoot ratio. Specific leaf area (SLA) which is the measure of leaf thinness, increased in plants under sUV-B exposure by 95.7 and 82.3% after 15 and 30 days after germination. Photosynthetic machinery of bean plants was the potential target of UV-B as photosynthetic rate was decreased by 88.6 % at 30 days after germination. sUV-B lead to the formation of reactive oxygen species thus generating oxidative stress. Stimulation of antioxidant defense system (enzymatic and non-enzymatic) was observed due to sUV-B radiation. Phenolic content decreased (34.7 and 18.6%) but protein showed varied response, increased initially (34%) thereafter declined (10.2%) under sUV-B radiation.

Response of ultraviolet-B induced antioxidant defense system in a medicinal plant, Acorus calamus.

Ultraviolet-B (UV-B) radiation generates an oxidative stress in plant cells due to excessive generation of reactive oxygen species (ROS). ROS can denature enzymes and damage important cellular components. In the present study, an important medicinal plant Acorus calamus (Sweet flag) was subjected to two doses of supplemental UV-B radiation (sUV-B): sUV1 (+1.8 kJ m-2 d-1) and sUV2 (+3.6 kJ m–2 d–1) to evaluate the relative response of antioxidant defense potential. Stimulation of activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) was observed at initial growth period while the activities of CAT and SOD decreased at later age of sampling. sUV-B induced lipid peroxidation (LPO) was observed showing alteration of membrane properties. No definite trend of change was observed for ascorbic acid (AsA), while increaments in thiol, proline, phenol and protein contents were observed due to sUV-B. Results suggested that sUV-B radiation may stimulate the enzymatic and non-enzymatic defense system of Acorus plants, showing its better adaptation at lower dose of sUV-B.

Response of ultraviolet-B and nickel on pigments, metabolites and antioxidants of Pisum sativum L.

Ultraviolet radiation (UV) though harmful but is an important and unavoidable component of terrestrial ecosystem to which plants have been exposed since their migration from aquatic to land habitat. Incoming UV-B radiation and heavy metals abundance in contaminated soils are significant environmental threat affecting metabolic functions of plants through generation of reactive oxygen species. Plants have evolved mechanisms to counteract these reactive radicals and to repair the damage caused by UV-B and heavy metals. This study describes the impact of supplemental UV-B (sUV-B) and nickel (Ni) singly and in combination on photosynthetic pigments, flavonoids, enzymatic and non-enzymatic antioxidants, metabolites and lipid peroxidation of Pisum sativum L. (pea) plants. Compared to the controls, both the stresses individually and in combination led to reductions in photosynthetic pigments, ascorbic acid, protein and catalase (CAT) activity, whereas a reverse trend was observed for flavonoids, phenol, proline and thiol contents, superoxide dismutase (SOD) and peroxidase (POX) activities and lipid peroxidation (LPO). However, flavonoids increased significantly under individual exposure of sUV-B as compared to other treatments. An increase of LPO by 81% indicated the generation of reactive oxygen species under both the stress conditions. sUV-B and Ni in combination acted synergistically with stimulation of CAT activity by 51.6% , additively on SOD activity with increase of 16.4%, while other parameters showed antagonistic action of both the stresses.

Combined effects of enhanced ultraviolet-B radiation and mineral nutrients on growth, biomass accumulation and yield characteristics of two cultivars of Vigna radiata L.

In a field experiment, the effect of enhanced UV-B radiation (simulating 20% ozone depletion at Allahabad, 20 degrees 47' N latitude) was studied on two cultivars of Vigna radiata L. with various levels of mineral nutrients (N and P). Study showed decrease in total biomass accumulation, harvest index, RSR and yield after exposure with enhanced level of UV-B. RGR and CGR also showed decline after exposure with UV-B. Application of recommended dose of mineral nutrients alleviated the deleterious effect of UV-B and increased plant dry matter vis a vis yield. Both cultivars showed sensitivity to UV-B but cultivar Malviya Janpriya was more responsive to UV-B than Malviya Jyoti.

Assessment of the pulp and paper mill effluent on growth, yield and nutrient quality of wheat (Triticum aestivum L.).

Assessment of agropotentiality of the effluent coming out from century pulp and paper mill, Ghanshyamdham, Lalkua (Uttaranchal) has been made on wheat (Triticum aestivum var. UP-2329) crop grown in two soils differing in texture with different effluent concentrations. Diluted effluent increased the chlorophyll content, plant height, shoot and root biomass, grain yield, protein, carbohydrate and lipid contents in wheat grains, while undiluted effluent caused inhibition in plant growth resulting in a sharp decline of yield. Pure soil provided better growth and yield results than those soil mixed with sand.