Alleviation of Cadminum Stress in Wheat by Exogenous Application of Moringa Leaf Extract and Ascorbic Acid

Abstract

Presence of hazardous heavy metals particularly cadmium (Cd) in agricultural soil of Faisalabad city is becoming a serious health hazard as well as loss in valuable nutritionous crops like wheat. To address such concerns, contemporary research was designed to investigate response of wheat at two morpho-physiological stages of wheat (Tillering & Boot) against cadmium. The mitigation of cadmium stress with economically and environmentally friendly osmoprotectant moringa leaf extract (3% aqueous) was addressed along with synthetic osmoprotectant ascorbic acid. Ascorbic acid is well known compound for its antioxidant properties. Moringa leaf extract also consist of many important micro and macronutrients which may be helpful for plant to recover from abiotic stresses. This diversified plant extract can be used as potential osmoprotectant against cadmium stress. To understand special effects of moringa leaf extract and ascorbic acid against cadmium stress in wheat, a pot experiment was designed in two consecutive years 2014-15 and 2015-16. The results presented in the form of graphs and tables are taken as average of two-year trial on wheat with proposed treatments. Growth attributes showed deleterious effect of cadmium alone but combine effect of cadmium with MLE resulted in enhanced growth, though it was slightly less than non-stresses (control) plants, but still effect of MLE followed by AsA was appreciatable on growth at 500µM Cd than other level of cadmium tested during current study. Inhibitory effect of cadmium was also observed in case of reduced photosynthetic activity, water related attributes and gas exchange attributes. This showed an overall effect of photosynthetic machinery and water balance of wheat cultivars under stress. Reduction in growth may be related to reduce photosynthetic activity and can be referred to as stress avoidance by plant to utilize its energy for developmental process at later stages. This may be the result of high photosynthetic rate at booting stage than tillering stage as data recorded in current experiment. MLE and AsA positively correlated with cadmium. Biochemical attributes also showed a negative response with both levels of cadmium. At the onset of cadmium stress, wheat cultivars start producing reactive oxygen species which effect wheat physiology. Lipid peroxidation was also enhanced with cadmium. But combined effect of cadmium and MLE caused mitigation of stress by decreasing lipid peroxidation and H2O2 activity. Ascorbic acid was also good enough to mitigate cadmium stress. Enzymatic and non-enzymatic antioxidants were also showed differential behavior with different treatments with and without cadmium at both stages of wheat. Cadmium (1000µM) treatment adversely affects plant by reducing SOD, POX, CAT and total soluble protein activity. This showed sensitivity for wheat cultivars at this level of cadmium stress while 500µM level of cadmium stress can be overcome by foliar treatment of MLE and AsA by producing enough antioxidants to manifest tolerance in wheat plant. For most of the enzymatic antioxidants, booting stage showed enhanced activity under stress to create tolerance in both cultivars. Galaxy-13 is more tolerant variety than Faisalabad-08 for enzymatic antioxidants. Non-enzymatic antioxidants also played potential role to combate cadmium with foliar application of MLE and AsA to enhance survival rate of wheat. A few of non-enzymatic antioxidanted like ascorbic acid, glycine betaine, proline, total soluble sugar, total soluble phenolics, alpha tocopherol, total free amino acid was tested to check their role as asmoprotectant and non-enzymatic antioxidant. Ascorbic acid activity was enhanced with cadmium stress which was further enhanced by MLE and AsA. Cadmium stimulated the innate mechanism of wheat by increasing ascorbate contents. All other osmoprotectants enhanced slightly with 500µM cadmium but adversely decreased with 1000µM cadmium. Potential phenolics like quercetin, gallic acid, ferulic acid, m-coumeric acid and chlorogenic acid accumulated in wheat with MLE at both stages. Data for yield attributes were collected only at boot stage. Yield of wheat attributes were judged for reduced number of fertile tillers, spikes and spikelets per plant and spike respectively and 1000 grain weight (g). MLE improved all above-mentioned parameters better than AsA by mitigating advere effects of cadmium stress in wheat.