Non-budding Hydra: Form Regulation and Bud Induction

Form regulation and bud induction were studied in a non-budding strain of Chlorohydra viridissima. Regeneration at a cut surface in a column piece with an existing hydranth was observed and found to be dependent on the column length Another aspect of form regulation, formation and control of supernumerary tentacles, was investigated by grafting. Supernumerary tentacle formation in long polyps can be suppressed by implants of hypostomal or subhypostomal tissue. Non-budding hydra can be induced to bud by implanting small pieces of normal tissue into their columns. The cellular basis of this process was investigated by means of grafting, radioautography, and histological methods. No differences in the proportions or appearances of the cell types were observed between non-budding and normal animals. However, induced buds have higher proportions of interstitial cells and their derivatives (nerves and nematoblasts) than do normal buds. Many of these interstitial cells and derivatives originate from cells in the grafted implant. Normal tissue from which interstitial cells have been previously removed will not induce buds in non-budding hydra. The non-budding syndrome is probably related to a deficiency in interstitial cell differentiation. If nerve cells are involved in bud initiation and form regulation, these results suggest interstitial cells of non-budding hydra are unable to transform into sufficiently active and/or numerous nerve cells to control those processes.