THE MOBILITY OF BORON IN PLANTS

In order to investigate a possible remobilization of boron, tomato plants were first exposed to excessive supplies of B and thereafter transferred to B-free nutrient solutions. Almost all the gain of top biomass after this transfer consisted of the growth of pre-existing immature leaves. Little new growth occurred before severe B deficiency became apparent. Boron was moved out of stems, but there was no evidence for a transfer of B from leaf blades into new tissues at the top. Although the B concentration in roots was low after the transfer to the B-free solution, there was a manyfold increase in root biomass. Consequently, the B content of the entire root system increased. It is concluded that little B was remobilized and transported into plant tops, whereas a small but adequate amount was remobilized and transported to the roots.