This study was conducted to examine the extent of oxidative stress and the role of antioxidant enzymes on hypoxia tolerance in highly tolerant wild species Vigna luteola, and mung bean (Vigna radiata) cvs. T 44 (tolerant) and Pusa Baisakhi (susceptible). contents. Hypoxia induced increase in superoxide dismutase, ascorbate peroxidase, and glutathione reductase activities were higher in T 44 and V. luteola compared with Pusa Baisakhi; and the increases in T 44 and V. luteola continued up to 8th day of water-logging, while in case of Pusa Baisakhi, the maximum increase was observed only on the 2nd day of water-logging. Gene expression studies showed enhanced expression of cytosolic-Cu/Zn-superoxide dismutase (SOD) and cytosolic-ascorbate peroxidase (APX) in the roots of waterlogged V. luteola and T 44, while little expression was observed in control or treated

Wheat (Triticum aestivum L.) cv PBW 343 was grown in Hoagland solution devoid of nitrogen (-N) under two CO 2 levels viz. ambient (380 lL L -1 , AC) and elevated (600 ± 50 lL L -1 , EC) for 20 days in growth chambers. The rate of uptake, assimilation and accumulation of nitrate was compared. At lows nitrate concentration up to 0.5 mM, rate of nitrate uptake was higher in EC grown seedlings as compared to AC. Under non-limiting supply of external nitrate, the rate of uptake declined in EC grown seedlings. Nitrate reductase (NR) activity increased in EC grown seedlings at low external concentrations of nitrate. However, AC grown plants showed higher NR activity, but at very high concentrations of nitrate. EC grown plants showed low level of accumulation of nitrate in shoots under limited nitrate availability, indicating lower influx towards storage pool and more availability of nitrate in metabolic pool. Increasing nitrogen (N) fertilization therefore may not compensate for slower NO À 3 assimilation rates under EC, as uptake and assimilation both decline under nitrate sufficient conditions. Effective management practices and changes in the pattern of fertigation may be required in response to rising atmospheric CO 2 levels for wheat production.

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Flooding is a crucial factor affecting crop growth and yield in low-lying rainfed areas. Systematic investigation of fl ooding survival mechanisms in tolerant species has deciphered molecular, physiological, and developmental basis of soil fl ooding (waterlogging) and submergence survival. Flood escape and quiescence strategies of deepwater and submergence-tolerant rice ( Oryza sativa ) plants are regulated by ethylene-responsive factor (ERF) transcriptional activators. Ethylene induces genes of enzymes associated with aerenchyma formation, glycolysis, and fermentation pathway. Nonsymbiotic hemoglobin (NSHb) and nitric oxide (NO) have also been suggested as an alternative to fermentation to maintain lower redox potential (low NADH/ NAD ratio). In rice ( Oryza sativa L.), a calcineurin B-like interacting binding kinase (CIPK; OsCIPK15) is also involved in hypoxia tolerance. Detailed investigation revealed that ERFs are targets of a highly conserved O 2 -sensing protein turnover mechanism in Arabidopsis thaliana . Transcriptome and metabolome profi ling of waterlogging-tolerant plant species reveals survival strategies that may be utilized through crop molecular breeding to develop tolerant cultivars. Keywords IntroductionExcess of water in the form of waterlogging (soil fl ooding) or complete submergence is lethal to majority of the terrestrial plants. Flooding events represent huge variation in duration and extent of inundation resulting in suboptimal levels of oxygen (hypoxia) or complete absence of oxygen (anoxia) affecting plant survival.

The objective of this study was to examine the role of nitrate reductase, nitric oxide and non-symbiotic hemoglobin in imparting waterlogging tolerance in mung bean genotypes. Experiment was conducted with two cultivated mung bean [Vigna radiata (L.) Wilczek] genotypes T 44 (tolerant) and Pusa Baisakhi (susceptible) and a highly tolerant wild species Vigna luteola (Jacq.) Benth. The content of nitric oxide increased up to 6 d of waterlogging in Vigna luteola and T 44, and up to 4 d of treatment in Pusa Baisakhi. Increase in nitrate reductase (NR) activity was observed only up to 4 d of waterlogging in Vigna luteola and T 44, and up to 2 d of treatment in Pusa Baisakhi, and thereafter the activity decreased in all the genotypes. The increase in NO content and NR activity was greater in Vigna luteola and T 44 than in Pusa Baisakhi. Non-symbiotic hemoglobin (NSHb) and cNR mRNA expressions were observed only in waterlogging treated roots of Vigna luteola and T 44, while very little expression was observed in control plants of Vigna luteola and T 44, and in control and waterlogged plants of Pusa Baisakhi. PCR bands of Hb and cNR were cloned, and nucleotide and deduced amino acid sequences were obtained and conserved regions and domains were identified using database.