Categories of Phloem Transport

Essentially, the phloem transport can be subdivided into the following:

1. The "loading" of the organic nutrients from the mesophyll cell into the phloem of the leaves,
2. Its translocation over long distances to the tissues awaiting supply,
3. The "unloading" of the nutrients from the phloem into the cells of the sink.

All these three processes are interlinked. The rate of transport is not constant but depends on the metabolic needs of the sinks on one hand and on the rate of photosynthesis in the leaves - the sources on the other. Phloem transport is a very complex phenomenon and we may indicate, at the beginning itself, that in spite of intensive research, it is not fully understood even today. As such this field offers a very challenging subject for future research in plant anatomy and physiology.