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.

The effect of protease digestion (in situ) on the slime substance of mature sieve tubes.

The sieve tube slime of Tetragonia and Lycopersicum petiolar phloem was subjected to proteolytic enzymes both before and after embedding and sectioning. Subsequent electron microscopical examination confirmed that the fibrillar material is protein in nature, and provided evidence that the protein is acidic rather than basic.