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A OOLCRIOLER SUSCEPTLBLUTY GRADIENT 18 OMLUM Hix B-Tr PBs
By Jouhua Lederberg?
Department of coolegy, und Department of Botuny
Columbia University.

Xt waa regognised by Levant in 1928 that the realte of the action
of coighigine on meristematio,aomatic tissues are not necesrerily a wnt
torm polyploidy. He states that after the treatment, on onion root-tips,
there ‘is “a deaided correlation between the chromosome number of a cell
and the position of the gell in the rout." The celle of higher ploiay
were found. in the proximal parts of the mer#atem. Thereafter, the aist-1
meristem was progressively reconstituted to the d&ploid number, possibly
by a dirierential division rate which favored the proliferation of dip-
icid celis. Such a phenomenon might account in part for some of the
vecnnieal ditiioul ties whieh are encountered in the use of coichicine
in the artificial prodnetion of polyploid plants,

Gn the basie of chunce observations on the ocuurrence of normul
mitoses in colohicine treated material,an investigation was undertaken
to determine whether or not there was an orderly,regulur differential
reaotion of dixsierent paxsts of the onion root to the netion ef aolonhi-
oine. ,

Colahicine efieats polyploidy through an inhibition of tne action
af the mitotia spindle. Although the centromere split is relutivedy
delayed, the chromosomal proceexes go shead as far as en initial, appar-
ently autonomous separation of the chromatids. Tne centromere does
finally eplit but there is no anaphase movement and the doubled nun-
ber of chromosomes i8 included ina uing.e ceetitution nugieus. The
name o-mitosia has been adopted for this prose: s.1t im ensily charac-

terizea by the failure of goorientation and congression, the absence
of spiile fibere in fixed material, and the ap earanve of separated
chromatids joined at a conspicuous centronere.?, 4.

Bulbs of the yellow onion,(Allium oepa).were germinated in &.p
water. After roots one to two centimeters long had appenred, the
water Was replaced with an aqueoue solution of colehicine (Colchicine
Alkaloid, amorphous, Mallinexrodt) at concentrations of £605 - ,058 4,
After a givan time of immersion in this solution the root tips were
fixed in Karpachenko or Bouin, dehydrated through dioxan, mounted in
pare, fin, and cut longitidinaliy at 8 micrones The sections were then
stained with Iron Haematoxylin, Newton's Violet, or Feulgen.

It soon appeared that mitoser and o-mitoser can exist in the same
Foot tip, but their relative distriltion is not Fandom. Invariatly,
mitoses were found in the distal,c-mitosees in the proximal portion
of the root. The sones of mitosis and of e-mitosis are go alstinet as
te leave no doutt as to the realit; of this phenomenon ,which was noted
in each of almmat a hundred roots. In transitional zones, tripalar
mistonea were very Occasionarly seen. In general, the effect of the
higher conoeniration of ecszaenicine ie to produce a relitively priguer
propertion of cemitoses, ana of the volume occupied by them in tne
Foot. The plane of demarcation betwee. ui6 two Zones does not xvremain
Btation-ry, tut moves distai.y,renohéng ite pesk,at whieh almost aal
division figures are c-mitotie, at about 11 hours of urea trent.

Considering the Ovaurrence of coms tosis as the Gytological inatoator
of tie celifs susceptibility to colchicine, these resul«: can be inter-
Pre teu u@ & graded susceptibility ,along the rovt's dongituainsl axis,
of the cells to colchicine. That diiierenitial permeablility,or tranc-
port mechanians,or intrinsic diitferences in the celi's phyeirlogy along
the line of this gradient may be diivelved, de :eaornized but the data
do not yet permit any decision among the various alternative hyfpotheces,
A macrorcopie result of the exrfrets of oolohioitne ie the induction
of a bulbous swelling, or ‘tumour, in the a:teoted root-vip, the mechan-
ims or the produe tion of which is stili oon wovexaiala»¥> ° A® thage
tnreshola concentrations, tue continued mitotio,ana oeli-proliferatory
activity of pari of tie meristem permits the formation of very elongate

tumours, some ane to tro ventimeters in Length,over a period of dare,

i. The author iv particularly indebged tu Dr. W.G. Vhaley, Depactuent
of Aotany,Colwibis University, for Pending toe mauugeript, ead providing
many OL vue fagiiitie: Lor bis work, Me ie alvo inaeberd to many rene
bers oF che “ooLogy Department for their srasious afsistance, und dip-
ouerion of the problem,

&. Sdillian Rayden emorial Bekdlw, Columbin Coliege.

5. “evan,\ibert, Hereditas,24, 471-466 (1936).

4. O''ara,J.G., Jour, Hered., 30, 38-87 (1939).

5. Huwrkes,7.G., Jour Genet.,4¢, lleze (1942).