Further evidence of apoplastic unloading into the stem of bean: identification of the phloem buffering pool

Further evidence that sucrose is passively leaked from the sieve tubes directly into the apoplast of bean stems and actively reloaded is reported. The stem apoplast is identified as the pool of sucrose outside the sieve tubes which buffers against sudden changes in sieve tube sucrose concentration, caused by sudden changes in sink demand or source supply.