BORON IN PLANT STRUCTURE AND FUNCTION

New and exciting developments in boron research in the past few years greatly contributed to better understanding of the role of boron in pl ants. Purification and identification of the first boron-polyol transp ort molecules resolved much of the controversy about boron phloem mobi lity. Isolation and characterization of the boron-polysaccharide compl ex from cell walls provided the first direct evidence for boron crossl inking of pectin polymers. Inhibition and recovery of proton release u pon boron withdrawal and restitution in plant culture medium demonstra ted boron involvement in membrane processes. Rapid boron-induced chang es in membrane function could be attributed to boron-complexing membra ne constituents. Boron may affect metabolic pathways by binding apopla stic proteins to cis-hydroxyl groups of cell walls and membranes, and by interfering with manganese-dependent enzymatic reactions. In additi on, boron has been implicated in counteracting toxic effects of alumin um on root growth of dicotyledonous plants. Molecular investigations o f boron nutrition have been initiated by the discovery of a novel muta nt of Arabidopsis thaliana with an altered requirement for boron.