P-proteins are group of proteins that express specifically in the sieve elements or parenchymatous cell of phloem tissues. They are filamentous, spherical, tubular, crystalline and amorphous in shape and their ontogenesis varied from species to species. Some of them are plant lectins and their coding genes have been sequenced. In the previous study, a 24 kDa phloem protein was obtained from phloem exudate of Luffa cylindrica fruits and it was immunofluoresciently located in the bicollateral phloem tissues of vascular bundles. In the present study, the intracellular localization of 24 kDa p-protein was examined with colloidal-gold immunolabelling.

Fruits of L. cylindrica were harvested for study. The outer parts of fruits containing exocarp and mesocarp were firstly cut into small cubes in dimensions of 2 x 2 x 6 mm, prefixed in 0.1 M phosphate buffer containing 4 % aldehyde mixture of paraformaldehyde and glutaraldehyde (3:1) for 4 h and washed with distilled water. The washed cubes were then trimmed into 1 mm cubes and postfixed in OSO4 for 2 h, dehydrated in a graded ethanol series and embedded in Spurr's resin.