THE ROLE OF RIBONUCLEIC ACID AND SULFHYDRIL GROUPS 



265 



with dithiodiglycol by intense mitotic activity, overdevelopment of the 

 head, reduction of the body, and lordosis. Dithiodiglycol has no par- 

 ticular e£Fect, in contrast to mercaptoethanol, on pigment formation. 

 Obviously many biological activities in amphibian embryos, at the 

 cellular as well as at the organismal level, are controlled by the 

 sulfhydril-disulfide equilibrium. 



Let us now examine an entirely different biological material, the 

 alga Acetabuloria mediterranea. As already mentioned, mercaptoetha- 

 nol (M/lOO) exerts a striking inhibitory effect on cap formation in 

 Acetahularia, especially in anucleate fragments ( Brachet, 1958b, 1959, 

 1960 ) . The algae, whether they are nucleate or anucleate, grow steadily 

 in the presence of M/300 mercaptoethanol, but they never form caps 

 (Figure 17). If small caps are present at the time of the section, they 

 never grow to an appreciable extent in anucleate fragments. On the 

 other hand, the production of the sterile whorls, which should normally 

 give rise to caps, proceeds almost unhampered. 



Since mercaptoethanol so strongly inhibits morphogenesis ( i.e., 

 cap formation) in Acetohularia as well as in amphibian embryos, it be- 

 comes of interest to study the effects of dithiodiglycol on this alga. The 

 results of these experiments were fairly clear: while mercaptoethanol 

 inhibited cap formation without exerting ill effects on the production 

 of whorls, dithiodiglycol (M/10,000) had exactly the opposite effect of 



Figure 17. Anucleate fragments of Acetahularia have formed only sterile 

 whorls after a 4-week treatment with M/300 mercaptoethanol. 



