Depicting the physiological and ultrastructural responses of soybean plants to Al stress conditions

Abstract

Aluminium (Al) is a toxic element for plants living in soils with acidic pH values, and it causes reductions in the roots and shoots development. High Al concentrations can cause physiological and structural changes, leading to symptoms of toxicity in plant tissue. The aim of this study was to describe the Al toxicity in soybean plants through physiological, nutritional, and ultrastructure analyses. Plants were grown in nutrient solution containing increasing Al concentrations (0; 0.05; 0.1; 1.0, 2.0 and 4.0 mmol L). The Al toxicity in the soybean plants was characterized by nutritional, anatomical, physiological, and biochemical analyses. The carbon dioxide assimilation rates and stomatal conductance were not affected by the Al. However, the capacity for internal carbon use decreased, and the transpiration rate increased, resulting in increased root biomass at the lowest Al concentration in the nutrient solution. The soybean plants exposed to the highest Al concentration exhibited lower root and shoot biomass. The nitrate reductase and urease activities decreased with the increasing Al concentration, indicating that nitrogen metabolism was halted. The superoxide dismutase and peroxidase activities increased with the increasing Al availability in the nutrient solution, and they were higher in the roots, showing their role in Al detoxification. Despite presenting external lesions characterized by a damaged root cap, the root xylem and phloem diameters were not affected by the Al. However, the leaf xylem diameter showed ultrastructural alterations under higher Al concentrations in nutrient solution. These results have contributed to our understanding of several physiological, biochemical and histological mechanisms of Al toxicity in soybean plants.

24-Epibrassinolide Improves Root Anatomy and Antioxidant Enzymes in Soybean Plants Subjected to Zinc Stress

“…Its world production reached 338 million tons in the 2017/2018 harvest, with the United States, Brazil and Argentina being the main producers (FAO 2018). In field conditions, it has been frequently observed that the growth and development of this species can be affected by abiotic stresses induced by nutritional imbalances (Wang et al 2015;Santos et al 2017), metal toxicity (Balasaraswathi et al 2017;Reis et al 2018), water deficiency (Kunert et al 2016;Wijewardana et al 2019), salinity (Shu et al 2017) and high temperatures (Allen Jr. et al 2018).…”

Physiological Parameters of Soybean Under Different Intensities of Artificial Light

“…The opening of stomata cleft can be proved with the values found in stomata conductance (gs), as Figure 3 shows, in which the light intensity acts in stomatas. Other factors also are linked to opening and closure of stomatal clefts such as nutritional stress and herbivory (Reis et al, 2018;Reis et al, 2017;Meza-Canales et al, 2017;Shrestha et al, 2018), H 2 O availability in the system soil-plant-atmosphere (Bellasio et al, 2017;Li et al, 2017) and inner morphology of plants (Stewart et al, 2017;Feldman et al, 2017;Xiong et al, 2017;Rockwell & Holbrook, 2017). These factors influences in leaves transpiration (Figure 3), that shows similar and linear responses between these two parameters, presenting a positive correlation between them.…”

“…It is worth noting that when the soybean is undergoing nutritional stress, the reactions processes in the photosynthesis and diffusion of CO 2 through the stomata and mesophyll act as co-regulators at the point of light compensation, while an increase occurs in the rate of breathing as reported by Singh and Reddy (2018). In this way, it is important to know the response mechanisms that leguminous plants act when they are exposed to quality and light intensities, as they can also suffer from competition with weeds for light, nutrients and water (Lisboa et al 2018). With an exposure that leads to overlapping, an action of Gibberellins (GAs) and auxin [indole-3-acetic acid (IAA)] play important roles in mediating adaptive responses to plant shading (Yang et al, 2018).…”

Differential accumulation of aluminum in root tips of soybean seedlings

“…Although the cell wall has been recognized as the main target of Al toxicity (Horst et al 2010;Yang et al 2011a, b;Gao et al 2014;Sun et al 2016;Safari et al 2018), it is proposed that the Al immobilization in the cell wall can play an important role as an Al tolerance mechanism (Yang et al 2008;Kochian et al 2015). Since Al is in the root cell wall, it can be complexed with organic acids (Kopittke et al 2017) or Al can bind to phosphorus (Al-P) (Yang et al 2011a, b;dos Reis et al 2018;Lu et al 2020), preventing its entry in internal tissues.…”

“…The phytotoxicity caused by Al negatively affects the productivity mainly of grain crops (Kochian et al 2004;Ryan et al 2011). Soybean, for example, is a relatively more acidsoil-sensitive plant in the presence of Al than other crops (Yang et al 2011a, b;dos Reis et al 2018). The sensitivity of soybean to Al is primarily due to its direct effect in the root system by binding to sites in the apoplast (Kopittke et al 2015).…”