Chromium(VI) Toxicity and Active Tolerance Mechanisms of Wheat Plant Treated with Plant Growth-Promoting Actinobacteria and Olive Solid Waste

Abstract

The present study aimed to assess the potential of plant growth-promoting Actinobacteria and olive solid waste (OSW) in ameliorating some biochemical and molecular parameters of wheat (Triticum aestivum) plants under the toxicity of high chromium levels in the soil. With this aim, a pot experiment was conducted, where the wheat plants were treated with a consortium of four Actinobacterium sp. (Bf treatment) and/or OSW (4% w/w) under two levels of nonstress and chromium stress [400 mg Cr(VI) per kg of soil] to estimate the photosynthetic traits, antioxidant protection machine, and detoxification activity. Both Bf and OSW treatments improved the levels of chlorophyll a (+47−98%), carotenoid (+324−566%), stomatal conductance (+17−18%), chlorophyll fluorescence (+12− 28%), and photorespiratory metabolism (including +44−72% in glycolate oxidase activity, +6−72% in hydroxypyruvate reductase activity, and +5−44% in a glycine to serine ratio) in leaves of stressed plants as compared to those in the stressed control, which resulted in higher photosynthesis capacity (+18−40%) in chromium-stressed plants. These results were associated with an enhancement in the content of antioxidant metabolites (+10− 117%), of direct reactive oxygen species-detoxifying enzymes (+49−94%), and of enzymatic (+40−261%) and nonenzymatic (+17− 175%) components of the ascorbate−glutathione cycle in Bf-and OSW-treated plants under stress. Moreover, increments in the content of phytochelatins (+38−74%) and metallothioneins (+29−41%), as markers of detoxification activity, were recorded in the plants treated with Bf and OSW under chromium toxicity. In conclusion, this study revealed that the application of beneficial Actinobacteria and OSW as biofertilization/supplementation could represent a worthwhile consequence in improving dry matter production and enhancing plant tolerance and adaptability to chromium toxicity.

Improving plant adaptation to soil antimony contamination: the synergistic contribution of arbuscular mycorrhizal fungus and olive mill waste

“…3). This result corroborates the results of a great deal of the previous research, in which the favourable effects of AMF and OMW treatments in declining the concentration of oxidative markers in stressed plants have been reported [5,7,19]. It seems possible that these results are due to the higher detoxification of ROS in AMF-and OMW-treated plants under stress, in which the antioxidant enzymes and molecules were more activated than those in stressed control plants.…”

“…The detoxification of overproduced ROS in plants has been reported to be attributed to the activation of the antioxidant defence strategies in response to OMW and AMF treatments [5,19]. Similar reports revealed higher levels of direct ROS-detoxifying enzymes (POX, SOD, and CAT) and antioxidant enzymes and metabolites involved in the ASC/GSH (ASC, GSH, APX, GR, MDHAR, DHAR, and GPX) can ameliorate the damaging effects of oxidative stress caused by heavy metals contamination [8,9,19].…”

“…The detoxification of overproduced ROS in plants has been reported to be attributed to the activation of the antioxidant defence strategies in response to OMW and AMF treatments [5,19]. Similar reports revealed higher levels of direct ROS-detoxifying enzymes (POX, SOD, and CAT) and antioxidant enzymes and metabolites involved in the ASC/GSH (ASC, GSH, APX, GR, MDHAR, DHAR, and GPX) can ameliorate the damaging effects of oxidative stress caused by heavy metals contamination [8,9,19]. In this regard, the response of ASC and GSH in both OMW-and AMF-treated plants under Sb contamination in the present research, as the non-enzymatic component of the ASC-GSH pathway, coordinated with the activation of involved enzymes, especially APX, which catalyze the reduction of H 2 O 2 into H 2 O [53].…”

“…The inoculation treatment was divided into two levels including (i) soil treatment with AMF inoculants and (ii) control treatment by adding the autoclaved inoculum in equal amounts to provide equivalent nutrients aside from mycorrhizal spores. To apply OMW treatment, soils were supplemented with 4% w/w of OMW after collecting from a traditional and air-drying for one month before use [19]. The physicochemical properties of OMW are presented in Table 1.…”

“…The topic of the organic amendments production for soil application from olive waste, containing an optimal level of nutritional values, received considerable critical attention within the scientific society [18]. One of those agricultural and food waste is olive waste which is generated by the olive oil manufacturing process and is known for its favourable impacts on plants, mainly under soil heavy metal contamination [9,19].…”