Changes in Intracellular Distribution of Thiol Groups During the Development of Acetabularia mediterranea

A cytochemical study of intracellular thiol distribution in Acetabularia mediterranea intact cells was performed using the fluorescent thiol-labelling agent monobromobimane (mBBr). Different developmental stages were examined during the vegetative phase and generative phase of the algal life cycle up to cyst maturation. Important changes in thiol localization have been found to coincide with turning-points ofAcetabularia development.During the rapid growth phase, overall thiol content steadily increased along the stalk, being maximal shortly before cap differentiation. At this stage, the thiol distribution pattern paralleled that of cap morphogenesis essential processes: thiols being accumulated at the apex where morphogenesis is going to be expressed.High thiol contents were also present in the rhizoidal part of the alga throughout the vegetative phase. At the onset of the generative phase, important alterations in rhizoid thiol distribution coincided with the presumptive time of nuclear division. Overall thiol content strongly decreased and thiols became highly concentrated in definite zones localized in the central area of the rhizoid.Later on, during the sequence of morphogenetic events leading to cyst differentiation, changes in thiol localization and relative content were observed in the cap rays. Positioning of secondary nuclei into the cap coincided with a high increase in thiol content in the entire cap. During the process of cyst formation, thiol content slightly decreased and thiols were localized in cyst domains.Thiol distribution was also studied during regenerative processes after merotomy. A spatio-temporal coincidence was shown with cell wall regeneration. © 1992 Oxford University Press.