studies of Nasatir and Stern (1959) on the activities of the glycolytic 

 enzymes, aldolase and triosephosphate dehydrogenase, during different 

 stages of the mitotic cycle of lily microspores have shown that the activi- 

 ties of these two enzymes are low during active mitosis. On the other 

 hand, the level of soluble — SH is high during this same period 

 (Figure 6-7). 



30 40 50 60 70 80 90 100 110 120 



Figure 6-7. Comparison of Variations in Soluble Sulfhydryl Concentra- 

 tion (solid circles) in Lily Anther Tissues, and Dehydrogenase Activities 

 (open circles) of Isolated Lily Microspores. (From Nasatir, M. and Stern, 

 H., 1959. "Changes in the Activities of Aldolase and of D-Glyceraldehyde-3- 

 Phosphate Dehydrogenase During the Mitotic Cycle in Microspores of 

 Liliiim longiflorum," J. Biophys. Biochem. Cytol., 6, Fig. 2, p. 191.) 



The metabolic processes which might.be operating to control the 

 redox cycle proposed by Mazia remain to be determined. While the 

 several schemes outlined by Mazia for the gelation of spindle protein 

 do not take into consideration the possible changes involved in dissolu- 

 tion of the spindle during anaphase-telophase, they do, however, suggest 

 ways in which such a breakdown could occur. The progressive dissolu- 

 tion of the spindle following metaphase would appear to involve, in part 

 at least, the cleavage of — SS — bonds. Because the covalent — SS — 

 linkage is relatively stable and not broken under the usual conditions of 



MECHANICS AND PHYSIOLOGY OF CELL DIVISION / 149 



