Tuber Vegetative Stages and Cell Cycle in Helianthus tuberosus: Protein Pattern and their Modification by Spermidine

This paper reports the protein amount and composition of tuber during its phases of formation, dormancy and sprouting. Parallely, the break of dormancy has been induced by excising slices of tuber parenchyma and treating them with 2,4-dichlorophenoxy acetic acid (2,4-D) to induce a new cell cycle; the protein composition, neosynthesis and post-translational modification by spermidine are reported during the phases of the cell cycle. From tuber formation to sprouting, protein content follows a bimodal trend. The protein bands were separated on sodium dodecyl sulfate polyacrylamide gel electrophoresis and two main bands (38 and 55 kDa) were detected. Many bands, especially of high molecular mass, changed their amount during all phases of tuber vegetative period. With the progression of the cell cycle very high molecular mass proteins increased; neosynthesis and modification by polyamines could account for this increase. Parallelly, the amount of lower molecular mass bands decreased. Many proteins are differently synthesized in the various cell cycle phases. Modification by spermidine occurred post-translationally, evident by an 18 kDa band (which in fact does not incorporate methionine), whose possible identification is discussed. A role for newly synthesized transglutaminases in the protein modification by polyamines is evaluated in the light of the immunodetection of 58 and 90 kDa bands by polyclonal anti-transglutaminase antibody.