Morphological and ultrastructural aspects of regeneration following wounding in the Udotea petiolata thallus.

Regeneration occurs in the Udotea petiolata thallus several weeks after wounding, the regenerative morphogenesis being similar to normal morphogenesis. Blade-like structures and rhizoids regrow with polarity. All tested regions of the thallus are able to regenerate, rhizoid production usually preceding blade-like structure growth, and cut stalks showing a faster and greater regenerative ability than cut blades. The first regeneration event is a branching bud in wounded siphons. Cytological changes during regeneration mainly involve assembly of several nucleic first in the subwound region and then in the branch tip. The ultrastructure of branch tip cytoplasm is compared with the cytoplasmic organization of the growing tip in the fringe of healthy thallus.