Phytohormones in plant responses to boron deficiency and toxicity

Abstract

Summary Boron (B) is an essential element for plant growth. Many agricultural soils around the globe have either insufficient or excessive amounts of available B, with major implications for crop production. Understanding major limitations imposed by B nutritional disorders may allow breeding crops for improved B use efficiency as well as make them more resilient to excessive B, thus reducing yield penalties. It has become apparent that B-related physiological disorders are mediated in large part by their impact on plant hormonal production and signaling. The aim of this review is to summarize the current knowledge of the roles of hormones in plant responses to B and their impact on plant growth and development. The most significant effect of B deficiency is the inhibition of root elongation. B deficiency promotes the redistribution of auxin in the root elongation zone. Together with cytokinin signals and ethylene, this redistribution and modulation of auxin content triggers inhibition of the root cell elongation. Under B deficiency, root development is also regulated by brassinosteroids and jasmonic acid. Excess B can induce the production of reactive oxygen species (ROS). Abscisic acid and salicylic acid are both produced in response to B toxicity, and both can induce the antioxidant defense system to detoxify ROS. Another adaptation to B toxicity involves changes in the expression levels and activity of aquaporins in roots, thus reducing the uptake of water and delivery of B into the transpiration stream. In addition, abscisic acid mediates stomatal closure to further limit transpiration and the consequent accumulation of B in leaves.

The Brassica napus boron deficient inflorescence transcriptome resembles a wounding and infection response

“…Jasmonic acid is a positive regulator of immunity against necrotrophic pathogens and herbivory (Berens et al, 2017). It has also recently been implicated in negatively regulating growth in response to B‐deficiency in A. thaliana seedlings (Huang et al, 2021a,b) and increased jasmonic acid biosynthesis under B‐limitation has been reported in B. napus (Zhou et al, 2016) and other species (Chen et al, 2022). WRKY transcription factors have also been shown to play diverse roles in plant defence, involved in both detection and the response to pathogens and other biotic stresses (Sarris et al, 2015; Jiang et al, 2017).…”

Synthesis and import of GDP‐l‐fucose into the Golgi affect plant–water relations

“…Importantly, the same structural defects were recently identified also in boron uptake mutant (Panter et al ., 2023) which implies a link between uptake of boron and morphology of OCLs. However, it cannot be excluded that the cuticle composition changes are a secondary effect of stress signaling (Voxeur et al ., 2017; Chen et al ., 2022). The precise function of OCLs is still poorly characterized (Hunt & Gray, 2020); however, changes in OCL structure provide little explanation for additive water loss observed in double mutants of mur1 and guard cell signaling components (Fig.…”

Linking the key physiological functions of essential micronutrients to their deficiency symptoms in plants

“…When reaching this zone, the local increase in auxin concentration, in combination with ROS accumulation, inhibits root elongation (Martín‐Rejano et al ., 2011; K. Li et al ., 2015). Furthermore, auxin stimulates the synthesis of ethylene (ET) precursors, which is a stress hormone that further promotes ROS accumulation, inhibits cell elongation in the root tips, and induces root hair formation (Martín‐Rejano et al ., 2011; Chen et al ., 2023b).…”