386 Colchicine 



16B.5: Chromosome Studies 



The pollen mother cells stained by acetocarmine are universally 

 a most important sovnxe for studying chromosomes in plants. The 

 procedure for determining the number of chromosomes is rapid. 

 More important than deciding what the number might be, are the 

 pairing characteristics at meiotic metaphase, chiasmatal frequencies, 

 lagging of chromosomes at meiotic anaphase, configurations due to 

 translocations, and the irregularities of meiotic jMocesses generally. 

 These are the problems associated with polyploidy that must be 

 studied at the pollen mother cell stage. 



Root tips are used for a check of the somatic numbers of chromo- 

 somes. Pretreatment of roots before fixation with chemicals that 

 arrest mitosis at metaphase facilitates the study.- Distributions of 

 chromosomes in an arrested metaphase are easier to count and com- 

 pare for size and morphology. i^- '*■ ^^- - 



Leaf cells in division combined with acetocarmine and Feulgen 

 technics are another source for counting chromosomes in polyploids 

 and related diploids. The longer period of time during which leaf 

 cells provide material and the abundance and availability of ma- 

 terial are favored in this test. 



Pollen tube cells that undergo mitosis in the tube rather than 

 inside the pollen grain can be treated with colchicine in sucrose-agar 

 media. Scattered chromosomes are easily counted, and the morphology 

 of somatic chromosomes in haploid sets can be measured. ^^ 



Causes of sterility in pollen and pollen mother cells may not be 

 the same when viewed in the embryo-sac stages, or among megaspore 

 mother cells. Frequently the polyploid may be pollen-sterile and 

 female-fertile, or vice versa. Transmission of certain extra chromo- 

 somes occurs only through the female and not through the male 

 gametophyte. Cytological methods to measure chromosomal varia- 

 tions in the female gametophyte are long and difficult procedures, 

 but they are important to a full knowledge of why some strains are 

 lower in fertility than others. 



REFERENCES — SECTION A 



1. Ashley, J. X., and Harris. J. O. Purification of colchicine by chromatogra- 

 phy. Jour. Chem. Soc. P. 677. 1944. 



2. AsTALDi, G., AND Mauri. C. La valutazione deH'attivita proliferativa delle 

 cellule miodlari. Studio di un "test stathmocinetico." Haematologica. 33:1-46. 

 1949. New criteria for the evaluation of the bone-marrow cells mitotic acti\ity. 

 LeSang. 21:378-82. 1950. 



3. , Bernardelli. E., and Rondanelli, E. La colchicine dans letude de la 



proliferation des cellides hemopoicticjues de I'embrvon. Rev. Beige Path. 

 21:406-13. 1952. 



4. Beams, H. W., and Evans, T. C. Some effects of colchicine upon the first cleav- 

 age in Arbacia punctulata. Biol. Bull. 79:188-98. 1940. 



