Abstract
Climate change exacerbates flooding problems due to hurricanes followed by heavy rains, particularly in sub-tropical regions. Consequently, submerged plants experience hypoxia stress which limits agronomic and horticultural crop growth and production. Hypoxia causes oxidative damage by accelerating the lipid peroxidation associated with O2- and H2O2 levels. Additionally, hypoxia increases the accumulation of organic osmoprotectants and antioxidant activity, whereas it decreases the macronutrient (N, P, K, and Zn) uptake. This study aimed at investigating the effects of flooding-induced hypoxia stress on the growth and the physiological, biochemical, and nutritional characteristics of the hydroponically grown southern highbush blueberry (cv. Jewel) plants. In addition, the hypoxia-mitigating effects of conventional silicon (Si-C) and silicon nanoparticles (SiNPs) and their application methods (foliar vs. foliar and rootzone application) were also appraised. Both the Si-C and the SiNPs efficiently alleviated hypoxia-induced oxidative and osmotic damage to cells by enhancing the activities of the enzymatic antioxidants (ascorbate peroxidase, catalase, dehydroascorbate reductase, superoxide dismutase, peroxidase, guaiacol peroxidase, monodehydroascorbate, reductase); the non-enzymatic antioxidants (ascorbic acid and glutathione contents); and the accumulation of compatible solutes (proline and glycinebetaine) in leaves and roots. However, the SiNPs were more effective than Si-C at improving antioxidant activities and osmolytes formation. A strong negative correlation between the antioxidant activities and the lipid peroxidation rate was observed in the SiNP-treated plants under hypoxia stress. The SiNPs also regulated nutrient uptake by increasing the K, N, P, and Zn concentrations while decreasing Fe and Mn concentrations to a less toxic level. Blueberry plants treated with SiNPs responded more effectively to hypoxia stress by maintaining higher antioxidant and osmoprotectant concentrations than blueberry plants treated with Si-C. Additionally, the foliar and rootzone applications yielded better results than the foliar applications only.
Highlights
Blueberries are referred to as a “super fruit” due to their high antioxidant capacity, their anthocyanin content, which contributes to the prevention of a variety of diseases, including cardiovascular disease, neurological disorders, and type 2 diabetes mellitus [1]
The plants grown under hypoxia stress with no supplemented Si had a significant reduction in leaf gas exchange traits, i.e., the net photosynthetic rate (Pn), the stomatal conductance, and the leaf greenness relative to the control plants
The current study significantly adds new information about the regulation of various physiological and biochemical characteristics in blueberry plants under hypoxia stress, and how the use of Si-C and silicon nanoparticles (SiNPs) helps the plants in mitigating hypoxia stress
Summary
Blueberries are referred to as a “super fruit” due to their high antioxidant capacity, their anthocyanin content, which contributes to the prevention of a variety of diseases, including cardiovascular disease, neurological disorders, and type 2 diabetes mellitus [1]. The consumption of blueberries (Vaccinium spp.) has attained particular interest due to their nutritious and health-beneficial features [1,2]. For these reasons, blueberry cultivation has been expanding rapidly from traditional cultivating areas to new production areas [3]. In the new and the conventional areas crop sustainability is reduced as there is a wider range of abiotic stresses, including high temperatures, salinity, drought, flooding, heavy metal toxicity, etc. Flooding causes a decrease in the leaf water potential, the net assimilation rate of CO2 , nutritional imbalances, hormonal alterations, and a higher accumulation of heavy metals and toxic substances, such as alcohols and aldehydes, as well as reactive oxygen species (ROS) [7,8]. Plants are equipped with an antioxidative defense system, which alleviates oxidative damage under stressed conditions, under more severe and prolonged stressed conditions, the antioxidant system does not remain strong enough to prevent the cell damage caused by lipid peroxidation and methyl-glyoxal accumulation [9]
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