Development and distribution of laticifers in plants

Abstract

Distribution, cytological organization and development of laticifers In some latex bearing plants were studied by the use of optical and electron microscopy. Seven species from five different families were used In a comparative study, which were Meconopsis cambrica & Papaver rhoeas (Papaveraceae), Hevea brasiliensis & Euphorbia wulfenii (Euphorbiaceae), Musa acuminata (Musaceae), Mandevilla splendens (Apocyanaceae) & Taraxacum officinale (Compositae/Asteraceae). Several preparation procedures have been compared and optimised for the structural preservation of the laticifers and for examination of their distribution in these taxa. Methods of fixation have been studied. Fresh unfixed samples showed good structural information and laticifer distribution in the tissue. This technique was also very fast and convenient to use. In practice this protocol can be applied in monitoring and screening bulk samples in a breeding program, where speed and convenience are very important. Samples fixed with aldehyde fixative gave reasonably good results for histology study but not at the electron microscope level. The samples fixed with this fixative however, were highly suited to Immunohistochemical work. This information is invaluable and will be used and adapted for Hevea study in Malaysia. Both osmium and a combination of osmium tetroxide and zinc iodide were superior in term of ultrastructural preservation. Embedding media for laticifers were compared. For histological and immunohistochemical studies, Paraplast wax was used. The preparation procedure was easy and convenient, and overall structural information of laticifers was good. Spurr resin and araldite are both epoxy resins, but samples embedded in araldite gave better, more acceptable results. The carcinogenic nature of Spun- resin means that it must be handled with extreme caution, making it a less convenient embedding medium. The only acrylic resin was LR White, which was initially Intended for an immunocytochemistry study where the priority was to retain antigenic sites. Samples embedded with this resin did not show good structural information. The final set of procedures evaluated was staining methods. The staining procedure has to be fast, must differentially stain laticifers and must be reliable. These stains can be grouped into two categories; standard histological stains such as Toluidine Blue and Safranin O with Astra Blue, and fluorescent stains such as Calcofluor, ANS and Acridine Orange. However almost all stains tested failed to differentially stain latex or laticifers. They however did assist in clarifying for identification the location and distribution of laticifers in the tissues. Using Toluidine Blue was very fast and easy, but all the fluorescent stains are faster and easier to use. Laticifers in all species examined, exhibited a similar pattern of distribution. They were located in the cambial regions of stems, petioles, leaves and roots, or closely located within the vascular bundle.