Boron in plants: a biochemical role.

Boron, as borate, appears to have a role in partitioning metabolism between the glycolytic and pentose-shunt pathways. This effect results from the association of borate with 6-phosphogluconic acid, forming a virtual substrate that inhibits the action of 6-phosphogluconate dehydrogenase. In the absence of borate, the inhibition of the enzyme is released, and excess phenolic acids are formed. These acids also associate strongly with borate and thus develop an autocatalytic system for production of excess phenolic acids which cause necrosis of tissue and eventual death of the plant.