Role of Boron in Vascular Plants and Response Mechanisms to Boron Stresses

To date, the primordial function of boron is its structural role in the cell wall through stabilization of molecules containing cis-diol groups (borate esters with apiose residues of rhamnogalacturonan II). Nonetheless, boron is a micronutrient also involved in a great variety of physiological processes in vascular plants. However the mechanisms underlying the various metabolic disorders caused by boron deficiency are indeed unknown. Recently it has been reported that boron deficiency and toxicity induce stress-responsive genes. In this contribution we review the mechanisms involved in boron uptake and distribution, the role of boron in vascular plants, the effects of boron deficiency and toxicity on them, as well as the interaction boron toxicity and salt stress. In addition, we discuss the most recent hypotheses proposed to explain how boron could exert its function in vascular plants from a mechanistic point of view. The importance of understanding the role of boron in plants as well as the response mechanisms to its deficiency and toxicity will allow us to improve the tolerance of crops to boron stresses. _____________________________________________________________________________________________________________