Distribution of boron within barley genotypes with differing susceptibilities to boron toxicity 1

The B toxicity resistance mechanism was investigated by examining the distribution of B amongst and within plant parts of four barley genotypes transferred from normal to excessive B. After transfer, the B concentrations increased in all plant parts. In corresponding parts (roots and leaves) however, the B concentrations always reflected the relative susceptibility of each genotype to B toxicity, with susceptible genotypes having higher B concentrations than less susceptible genotypes. Despite large differences amongst genotypes in the B concentrations of corresponding leaf segments, the relative B concentrations along the leaves were similar for all genotypes.

Similarly, the amount of B in all parts increased after transfer, with B accumulation by leaves closely reflecting leaf size. Roots contained up to 10 percent of the total B accumulated at each harvest. This pattern was essentially the same for each genotype at each harvest, despite the large differences in total B accumulated. These results show that the pattern of B distribution was remarkably similar in the four genotypes examined despite great differences in the total amounts of B absorbed and the actual B concentrations of individual parts. Differences amongst barley genotypes in susceptibility to B toxicity do not result from an ability to control the internal distribution of the element, but rather are governed by the amount of B each accumulates.