Localisation of adenosine triphosphatase activity in mature sieve elements of Tetragonia.

In the mature phloem of Tetragonia expansa strong ATPase activity is present on the plasmalemma of the companion cells and sieve tubes, and probably on the ER of the latter. The sieve tube wall sometimes shows a lead deposit. When the tissues is pre-treated with DNP there is often a diffuse deposit also on the P-protein and on the fibrillar protein from ruptured plastids. This is believed to be a diffusion artefact, and not to represent genuine P-protein activity.