Physiological and Molecular Analyses of Drought Tolerance Responses in Amaranthus ( Amaranthus tricolor L . ) under Elevated Carbon Dioxide Environments

The level of CO2 in the atmosphere is rising at an unprecedented rate. According to NOAA, 2014 global concentration of CO2 has reached 400 ppm for the first time in recorded history [1]. This rise, along with other trace gases in the atmosphere is widely thought to be a primary factor driving global climate change. Moreover the report of IPCC, 2012 [2] has reconfirmed the increasingly strong evidence of global climate change and projected that the globally averaged temperature of the air would rise by 1.8–6.4°C by the end of the century. Increase in global average temperatures would further result in drastic shifts in the annual precipitation with a 20% reduction per year and about 20% loss in soil moisture [3] and can increase potential evapotranspiration, leading to a more severe water deficit in arid and semiarid areas. Carbon dioxide is the key substrate for plant growth as it represents the sole source for carbon (C), which is limited by present-day CO2 concentrations [4]. Increased CO2 concentration has been found to ameliorate water stress in the majority of species studied. Under elevated CO2 conditions, plants adopt many mechanisms to maintain high water potential and to resist water scarcity. Different experimental techniques led to the conclusion that plants grown under elevated CO2 possessed increased root surface and root volume due to increased allocation of carbon to root growth [5]. Such increase in the surface area of roots enables the plants grown under elevated CO2 to exploit more water even from deep soil layers. However, the decrease in stomatal conductance may also be offset by increased leaf area in plants grown under elevated CO2 and thus water use by the whole plant may not be proportional to stomatal conductance. CO2 enrichment causes Abstract The level of CO2 in the atmosphere is rising at an unprecedented rate. According to NOAA, 2014 global concentration of CO2 has reached 400 ppm for the first time in recorded history and its concentration is expected to increase about 550 ppm within next 50-100 years. Carbon dioxide is the key substrate for plant growth as it represents the sole source for carbon (C), which is limited by present-day CO2 concentrations (Webber et al., 1994). Increased CO2 concentration has been found to increase water use efficiency in the majority of species studied. To understand the physiological and biochemical basis of varietal responses of amaranthus to water stress conditions and to study their modifications under CO2 enriched environment, a pot culture experiment was conducted with three varieties of amaranthus i.e, Arun (V1), CO -1 (V2) and Renusree (V3) in the Open Top Chambers (OTC) system. Plants were subjected to water stress during their critical stages of development and then were allowed to recover. Various biochemical and growth parameters like free amino acids, reducing sugar content, total dry matter content and antioxidants like ascorbic acid content were analysed to understand the effect of CO2 enrichment on drought tolerance. Electrophoresis analysis of proteins was analysed using SDS PAGE. Elevated CO2 was found to increase total dry matter production (0.99 g), reducing sugars (15.98 mg/g), free amino acids (1.19 mg/g) and ascorbic acid (116.31 mg/100g) content. Agriculture and allied sectors being the most vulnerable to climate change; it is an urgent imperative that adaptive strategies need to be developed for sustaining an enhancing agricultural production for achieving food security to an ever increasing population and to design improved production technologies with suitable varieties for a changing climatic scenario.