CELL DIVISION 



773 



The latter is apparently active only in the glycosidic form. These last two have 

 been evaluated on carrot tissue fragments (Steward and Shantz, 1956) using a 

 medium in which ions, sugar and casein hydrolysate are supplied. They give rise 

 to large numbers of small cells, some of which remain attached while others float 

 off into the solution and grow into new tissue masses. When synthetic auxins are 



GOGH 

 I 



CH 

 II 

 CH 



(CHsJg 



GOGH 



"Traumatic acid" 

 XXVI 



GgH^NH^ 



C=0 



/ 



CfeHsNH 



I, 3-Diphenylurea 



XXVII 



o ^e^iiOs 



Leucocyanidin monoglucoside 

 XXVIII ' 



added, the cells enlarge. Without casein hydrolysate, the effects are much smaller. 



While the material in coconut milk is present at all stages of the fruit's develop- 

 ment, the corresponding material in ^ea mays decreases rapidly 2 weeks after 

 pollination (Steward and Caplin, 1952). As far as its chemistry has been studied 

 the active fraction appears to be nitrogenous and closely associated with the amino 

 acids (GyorfFy et al., 1955) ; its action is complicated by the large amount of auxin 

 present {cf. Fig. 12, p. 809). 



A curious observation is that the synthetic auxin, benzothiazole oxyacetic acid, 

 XXIX, has a very powerful effect on cell division in artichoke, even exceeding 

 that of coconut milk (Steward and Shantz, 1956). It is much less effective on 

 carrot tissue. 



Probably the most powerful individual substance causing cell division so far 

 isolated is kinetin, or 6-furfurylamino purine, XXX. This compound is formed by 



CH 



■CH 



NH— GH, — C. X 



I ^ ^o-^ 



C— OCHjCGGH 



Benzothiazole oxyacetic acid 

 XXIX 



GH 



II 



N- 



C N 



^_ 



G-Furfurylamino purine (Kinetin) 

 XXX 



heating or autoclaving yeast nucleic acid (Miller ('Z (3/., 1955a, b, 1956; Strong, 1958) 

 and it (or a related compound) may be naturally present in traces in some samples 

 of nucleic acids. So far it has not been demonstrated in plant tissues, though its 

 occurrence there seems very probable. Its action on tobacco pith tissue cultures is 

 very powerful {cf. section IIIc, p. 759). On carrot tissue, in presence of lAA, 

 it is about 20% as effective as whole coconut milk, but on artichoke tissue its 

 activity is rather weak (Steward and Shantz, 1956). 



As in the above cases, its action is interrelated with that of auxin, and the effect 

 depends on the balance between the concentrations of the two substances (see 

 Fig. 2). Auxin alone causes root initiation in these cultures, kinetin added alone 



Literature p. 8t6 



