Silicon Differently Affects Apoplastic Binding of Excess Boron in Wheat and Sunflower Leaves

Abstract

Monocots and dicots differ in their boron (B) requirement, but also in their capacity to accumulate silicon (Si). Although an ameliorative effect of Si on B toxicity has been reported in various crops, differences among monocots and dicots are not clear, in particular in light of their ability to retain B in the leaf apoplast. In hydroponic experiments under controlled conditions, we studied the role of Si in the compartmentation of B within the leaves of wheat (Triticum vulgare L.) as a model of a high-Si monocot and sunflower (Helianthus annuus L.) as a model of a low-Si dicot, with the focus on the leaf apoplast. The stable isotopes 10B and 11B were used to investigate the dynamics of cell wall B binding capacity. In both crops, the application of Si did not affect B concentration in the root, but significantly decreased the B concentration in the leaves. However, the application of Si differently influenced the binding capacity of the leaf apoplast for excess B in wheat and sunflower. In wheat, whose capacity to retain B in the leaf cell walls is lower than in sunflower, the continuous supply of Si is crucial for an enhancement of high B tolerance in the shoot. On the other hand, the supply of Si did not contribute significantly in the extension of the B binding sites in sunflower leaves.

Molecular, Metabolic and Physiological Responses to Boron Stress in Higher Plants

“…Sunflower Leaves [21] B toxicity problems often occur in crops of arid/semiarid regions with low rainfall and high water evaporation where B accumulates in the uppermost layers of the soil, reaching toxic levels for plants. Alleviating the symptoms of B toxicity in crop plants can be achieved by applying elements that have a positive impact on the physiological tolerance of plants (i.e., those preventing oxidative stress).…”

“…Alleviating the symptoms of B toxicity in crop plants can be achieved by applying elements that have a positive impact on the physiological tolerance of plants (i.e., those preventing oxidative stress). For instance, Savic et al [21] demonstrated that Si fertilization significantly decreased B concentration in wheat (Triticum vulgare L.) and sunflower (Helianthus annuus L.) leaves when growing under high-B conditions, leading to a recovery of plant growth, especially in wheat. Interestingly, Si application increased the B-binding capacity of the leaf apoplast in wheat but not in sunflower.…”

Silicon Enhances Brassica napus Tolerance to Boron Deficiency by the Remobilisation of Boron and by Changing the Expression of Boron Transporters

“…Nevertheless, in a recent study, no clear positive influence of Si could be observed in rapeseed plants under S deficiency: Si supply did not increase the biomass or S content in these conditions [39]. Regarding B and Si interaction, most of the work has been focused on the effect of Si in alleviating B toxicity [40][41][42][43][44][45]. For instance, the work done by Inal et al (2009) demonstrated that the application of Si increased the level of non-enzymatic antioxidant activity and the activities of major antioxidant enzymes like superoxide dismutase, catalase and ascorbate peroxidase in barley plants under B toxicity [41].…”

Analogy of silicon and boron in plant nutrition

“…It has been reported that a supply of Si can alleviate the symptoms induced by B disorder in plants ( Pavlovic et al., 2021 ). Indeed, Si alleviation of B toxicity was reported in many plants, including rice, cotton, wheat, barley and others ( Gunes et al., 2007a ; Gunes et al., 2007b ; Inal et al., 2009 ; Chen et al., 2019 ; de Souza Junior et al., 2019 ; Savic et al., 2023 ). The formerly suggested common mechanism is that silicic acid interacts with the boron acid in soil solution and inside the plant roots to form Si-B complexes, leading to the B immobilization and reduced uptake of B ( Inal et al., 2009 ).…”

“…Moreover, Si raises the level of BOR2 gene expression, whose protein product serves as an efflux transporter for B extrusion, thereby contributing to B detoxification in the apoplast (Akcay and Erkan, 2016). Very recently, Savic et al (2023) found that Si can enhance the tolerance of B toxicity by the extension of the cell wall binding sites for B in the Si-accumulating species of wheat, but not in the Si-non-accumulating plant of sunflower. These findings imply the complicated roles of Si in B toxicity responses in different plants.…”