Nayan Sahu

Searching for common responsive parameters for ozone tolerance in 18 rice cultivars in India: Results from ethylenediurea studies

Eighteen rice (Oryza sativa) cultivars were screened for ozone (O3) tolerance and for the most responsive parameters with ethylenediurea (EDU) treatments at two experimental sites experiencing high ambient O3 conditions in the Indo-Gangetic Plains (IGP) of India. EDU was applied at 15 day intervals until the final harvest phase as a foliar spray at 300 ppm in order to protect the plants from the adverse effects of O3. Antioxidant activity, malondialdehyde content (MDA), chlorophyll content, gas exchange, and chlorophyll fluorescence (Fv/Fm) at the vegetative and flowering phases and harvest-related parameters were studied, for a total of 24 parameters. Seven of the studied cultivars had higher than average grainweightplant(-1) in all site and treatment combinations and can be recommended for cultivation in areas suffering from high O3 concentrations. The most responsive parameters with EDU treatment in high O3 across all cultivars were superoxide dismutase (SOD) and catalase (CAT) activities, the contents of oxidised (GSSG) and reduced (GSH) glutathione and MDA, and shoot weight plant(-1). These results indicated that the O3 scavenging activity of EDU is mediated through an antioxidant defence system rather than a direct effect on physiological parameters, such as photosynthesis and stomatal conductance.

Response of two rice cultivars differing in their sensitivity towards arsenic, differs in their expression of glutaredoxin and glutathione S transferase genes and antioxidant usage.

Embodied study investigates the role of GRX and associated antioxidant enzymes in the detoxification mechanism between arsenic (As) sensitive (Usar-3) and tolerant cultivar (Pant Dhan 11) of Oryza sativa against As(III) and As(V), under GSH enriched, and GSH deprived conditions. The overall growth and physiological parameters in sensitive cultivar were lower than the tolerant cultivar, against various treatments of As(III) and As(V). The As accumulation in sensitive cv. against both As(III) and As(V) was lower than the corresponding treatments in tolerant cv. However, the As translocation against As(V) was lower (35% and 64%, resp.) than that of As(III), in both the cultivars. In sensitive cv. translocation of Zn and Cu was influenced by both As(V) and As(III) whereas, in tolerant cv. the translocation of Cu, Mn and Zn was influenced only by As(III). Translocation of Fe was negatively influenced by translocation of As in sensitive cv. and positively in tolerant cv. Strong correlation between H2O2, SOD, GRX, GR, GST and GSH/GSSG in sensitive cv. and between DHAR, APX, MDHAR and AsA in tolerant cv. demonstrates the underlying preference of GSH as electron donor for detoxification of H2O2 in sensitive cv. and AsA in tolerant cv. Higher expression of the four GRX and two GST genes in the sensitive cv. than tolerant cv, suggests that under As stress, GRX are synthesized more in the sensitive cv. than tolerant cv. Also, the expression of four GRX genes were higher against As(V) than As(III). The higher As accumulation in the tolerant cv. is due to lower GST expression, is attributed to the absence of thiolation and sequestration of As in roots, the translocation of As to shoots is higher.

Selenite supplementation reduces arsenate uptake greater than phosphate but compromises the phosphate level and physiological performance in hydroponically grown Oryza sativa L.

The present study evaluates the reduction of arsenate (As[V]) uptake in rice seedlings through individual and combined supplementation of phosphate (PO4(3-)) and selenite (Se[IV]) in a hydroponic condition. The toxic response in seedlings receiving As(V) manifested as inhibition in physiological parameters such as water use efficiency, stomatal conductance, photosynthetic assimilation rate, transpiration rate, photochemical quenching, and electron transport rate, along with growth. Arsenic accumulation significantly decreased with Se(IV) treatment (0.5 μg mL(-1), 1 μg mL(-1), and 2 μg mL(-1)) in a dose-dependent manner (20%, 35%, and 53%, respectively); however, it compromised the PO4(3-) level and physiological performance. The lower level of Se(IV), (0.5 μg mL(-1)), was relatively beneficial in terms of reduction in As accumulation than the higher level of Se(IV), (2 μg mL(-1)), which was rather toxic. Further, decrease in As uptake, replenished the level of PO4(3-) and physiological performance in seedlings treated with As+Se+P compared with those treated with As+Se. However, supplementation with only PO4(3-) (10 μg mL(-1) and 20 μg mL(-1)) along with As(V) was less effective in reducing As accumulation compared with As+Se. Seedlings receiving As+Se+P also exhibited lower thiobarbituric acid-reactive substances (TBARS) and electrical conductivity levels compared with both As+Se and As+P. Among all the treatments, the activity of antioxidant enzymes was highest in plants treated with As+Se+P. Hence, the higher antioxidant enzyme activity in As+Se+P along with lower levels of TBARS, H2 O2 , and As accumulation are attributed to the competitive reduction in As uptake in the presence of Se(IV) and PO4(3-).

GABA accretion reduces Lsi-1 and Lsi-2 gene expressions and modulates physiological responses in Oryza sativa to provide tolerance towards arsenic

GABA counteracts wide range of stresses through regulation of GABA shunt pathway in plants. Although, GABA assisted tolerance against As toxicity in plants is still unexplored. We have examined GABA induced tolerance in rice seedlings with two exposure periods of GABA i.e., short term and long term. Results showed that accumulation of GABA reduced the expressions of Lsi-1 and Lsi-2 transporter genes, which ultimately decreased the accumulation of As in rice seedlings. The accumulation of GABA also modulated the gene expression of GABA shunt pathway and activity of antioxidant enzymes, which strongly induced the tolerance in plants. Antioxidant enzymes such as CAT, POD, GPX and SOD showed maximum alteration in activity with GABA accretion. In both exposure periods, long term accumulation of GABA was highly efficient to provide tolerance to plants against As(III), while higher level of GABA at short term was toxic. Tolerance responses of GABA towards As(III) was reflected by minimal changes in various physiological (WUE, A, gs, PhiPS2, qp, NPQ, ETR and Trmmol) and growth parameters with concomitant accumulation. Oxidative stress marker such as TBARS and H2O2 contents were reduced with GABA accumulation. These results suggested that GABA sturdily inhibits As accumulation and provides tolerance towards As(III).

Relation of Forest Structure and Soil Properties in Natural, Rehabilitated and Degraded Forest

Relation of Forest Structure and Soil Properties in Natural, Rehabilitated and Degraded Forest Plant community structure, species diversity and soil properties of natural, rehabilitated and degraded forests were studied in order to assess relationship of different forests structure and soil properties in upper Indo-Gangetic plain of Uttar Pradesh state of India. The composition of species, population bundance and importance value of the woody species were investigated in each forest; the representative soil samples from 30 cm depth of each forest were also analyzed for the soil properties. Dominant families at the natural forest are Moraceae (21.9%) and Rubiaceae (15.6%) while at the rehabilitated forest are Moraceae (53.8%) and Fabaceae (23%). In the degraded forest, the Moraceae and Fabaceae are dominant families occupy 33% each. These among forest community structure indicate that degraded forests are less complex ecosystems than natural forest stands.