Role of boron and its interaction with other elements in plants

Abstract

Boron (B) is an essential microelement for plants, and its deficiency can lead to impaired development and function. Around 50% of arable land in the world is acidic, and low pH in the soil solution decreases availability of several essential mineral elements, including B, magnesium (Mg), calcium (Ca), and potassium (K). Plants take up soil B in the form of boric acid (H₃BO₃) in acidic soil or tetrahydroxy borate [B(OH)₄]^- at neutral or alkaline pH. Boron can participate directly or indirectly in plant metabolism, including in the synthesis of the cell wall and plasma membrane, in carbohydrate and protein metabolism, and in the formation of ribonucleic acid (RNA). In addition, B interacts with other nutrients such as Ca, nitrogen (N), phosphorus (P), K, and zinc (Zn). In this review, we discuss the mechanisms of B uptake, absorption, and accumulation and its interactions with other elements, and how it contributes to the adaptation of plants to different environmental conditions. We also discuss potential B-mediated networks at the physiological and molecular levels involved in plant growth and development.

Keywords: boron; interaction; low pH; mineral elements; oxidative stress; protein transport.

Figure 1

Molecular interaction of B with other elements. (1). Boron interaction with Ca²⁺. Boron deficiency has been associated with changes in the expression of Ca²⁺ genes (ACA, CAX, CNCG) that are activated to restore Ca²⁺ homeostasis within the cytosol. (2) Boron interaction with N. Under B deficiency, nitrate transporters are downregulated affecting H⁺-ATPase transcripts and leading to ammonium accumulation along with elevated glutamine and asparagine production. (3) Boron interaction with K. AGP transcripts have been studied in the B x K relationship. Under B deficiency, these proteins are downregulated leading to changes in the membrane-cytoskeleton continuum in which an unknown cascade of signals is thought to be activated. (4) Boron interaction with Al. B has been studied as an alleviator of Al toxicity. Through different mechanisms and regulation of transport-related genes, B induces protein expression to reduce the deposition of Al in the cell wall and diminish its toxicity by importing it into vacuoles. (5) Boron interaction with Si. Si and B interact using the same NIP transporters, possibly allowing for B detoxification when found in high levels. (6) Boron interaction with Cd. Interestingly, B and Si when combined display an inhibitory activity over Cd transporters, accounting for the elimination of Cd toxicity. (7) Boron interaction with P. Under low B conditions, changes in BnaPT transporter expression regulates P content. Otherwise, under B toxicity and low P conditions, the transporters BnaC3 and SPX3 are upregulated to balance P content. (8) Boron interaction with Zn. Zinc finger proteins are upregulated in response to B toxicity. It is believed that these proteins regulate B content by stress signal transduction pathways to improve plant growth and development. These observations have been studied in different plant species and are not necessarily equivalent in all species. Created with Biorender.