Recently several new evidences have appeared on biological role of native short peptides. This is an overview on two of them occurring in plants: systemin and ENOD 40.
The presence and location of specific binding sites for progesterone and 17β-estradiol in cells of wheat were estimated using radioligand binding assay. Membrane and cytosolic fractions of non-vernalized and vernalized plants were tested using tritium-labelled ligands. Specific binding of [3H]progesterone and [3H]17β-estradiol occurs in wheat cells. The binding sites are located in membranes and in the cytosol. Specific binding of [3H]17β-estradiol is higher in the membranes than in the cytosol. Specific binding of both ligands in the cytosolic fraction is higher in vernalized plants than in non-vernalized ones. The possibility of the occurrence of steroid binding proteins specific for progesterone and 17β-estradiol, putative steroid receptors for these steroids in Triticum aestivum L., is discussed.
This short review emphasizes the importance of secreted molecules (peptides, proteins, arabinogalactan proteins, PR proteins, oligosaccharides) produced by cells and multicellular structures in culture media. Several of these molecules have also been identified in planta within the micro-environment in which the embryo and endosperm develop. Questions are raised about the parallel between in vitro systems (somatic and androgenetic) and in planta zygotic development. A view of exchanges between embryonic and nonembryonic multicellular structures in vitro is presented, and several facts about embryo and endosperm molecular interactions in planta are reported. Analysis of in vitro mechanisms may help in understanding what happens during zygotic embryogenesis.