Boron mobility in plants

Abstract

In the majority of plant species, B distribution between plant organs and the symptoms of B deficiency and toxicity indicate that B has restricted mobility. Nevertheless, B is present in phloem and is retranslocated in phloem, often in sufficient amounts to satisfy the demands of developing sink regions that do not readily transpire. In species that produce significant amounts of polyols in source leaves, boron is readily translocated as a consequence of the formation of B-polyol complexes. Boron is thus unique among the essential plant nutrients in that it has restricted mobility in many plant species and is freely mobile in others. No other element is known to vary so greatly in mobility. The retranslocation of B has a profound effect on the expression of B deficiency and toxicity symptoms, and the approaches needed to diagnose and correct B imbalances. Examples of the impact of B mobility on B uptake, B diagnosis, B toxicity and the breeding of species for B tolerance, are discussed here and in the relevant chapters of this volume. In the following we provide a summary of current information on the mobility of B in plants and provide insights into the physiological and agronomic consequences of these findings.