32 Colchicine 



In animal cells the prophase stages were thought to be non- 

 susceptible to colchicine because the drug did not penetrate the 

 nuclear membrane.*'- Theretore chromosomes remained as usual until 

 the membrane disappeared. Then the chromosomes came in contact 

 with the drug present in the cytoplasm. Alter this period, contraction 

 might take place.'^- '• "^' ^^' ^^ 



From plant tissues, fixed and stained, three important changes 

 were compared at prophase. ^^ First, chromatin threads developed 

 the minor spiral in both instances. Second, the major spiralization 

 proceeded along usual patterns. Third, chromosomes condensed into 

 proportioned prophasic structures as this stage ended. The two dis- 

 tinct chromatids were strongly cleaved, appearing as longitudinal 

 pairs twisted about each other in a relational coil (Fig. 2.1{)A) . On 

 these three points no noticeable differences among fixed and stained 

 cells, treated and luitreated, were observed.''^ But such opinions 

 about the action of colchicine at prophase required modification as 

 new techniques'-^' ^^- ■^'* replaced traditional cytological methods, and 

 a wide range of concentrations was included. 



Living cells were observed continuously from prophase through 

 all mitotic stages in Tradescantia staminal hair cells. '-^ By this method 

 colchicine could be applied at any stage chosen by the investigator, 

 who then followed the effects from that particular stage on through 

 sidDsequent ones. 



Strong concentrations (2 per cent) admitted dining mid-prophase 

 at the stage when chromosomes were condensing, caused the process 

 to revert back to an interphasic dispersion of chromatin.''-^ The time 

 schedule tor this reversion showed that a metaphasic arrest had not 

 been reached, but the restitution nucleus w^as formed from a mid- 

 prophase stage. In some cases the rcstitiuion nucleus appeared to be 

 doubled for chromosomal number. Similar cases were reported for 

 Siredou (Fig. 2.9A-D) .-^- "^^ This is one type of transformation Irom 

 prophase to interphase. 



Time schedules for the formation of chromosomes in projjhase 

 have been made with Tradescantia. This phase is called the anachro- 

 tnasis^'^ period of chromosomes. Untreated cells require 97 minutes 

 from early prophase to the polar cap stage. Longer time is taken in 

 the presence of 0.05 per cent (121 min.) , biu a mininunn time in 0.1 

 per cent (84 min.) is less than control. These concentrations permit 

 the chromosomes to move into the arrested metaphase, whereas a 

 stronger solution induces interphase. Colchicine slows down the pro- 

 cess of anachromasis as it occurs in prophase. To contrast these de- 

 velopmental processes, new methods had to be developed. 



The neuroblastic cells of grasshopper are used in another tech- 

 nique'^" with unusual possibilities for a different inspection of c- 



