Long distance transport of assimilates is shown to exist in soybean plants

Effect of source-sink distance on soybean yield was studied. Our hypothesis was that soybean can redistribute assimilates from lower leaves to young pods formed at youngest part of stems across the main stem to maintain yield. We artificially created two, four, six, eight, and ten-nodes of source-sink distances in soybean plant. A reduction in the seed yield of remained sink occurred with the increase in distance from the source. This was mostly due to a reduction of pod number caused by the increase of the distance from the source. No pod reduction was found at the 2-node distance compared with control plant. Reduction in seed size occurred for the 2- and10-node distance from the source. When source-sink distance was four, six, eight nodes, seed size was similar to control. Our findings suggest soybean plants are able to transport and use assimilates as far as 8 nodes distance. The successful translocation of assimilate from lower nodes is mainly used for pod formation and seed filling over a short distance, but can be translocated over a long distance and used for growth of remaining seed. This suggests the reproductive sink of soybean plants has an internal mechanism to off-set yield loss to ensure seed survival.