572 



R. M. Sachs and A. Lans: 



AMO-1618-INDUCED INHIBITION OF STEM ELONGATION 



IN CAULESCENT PLANTS 



Extensive work in the U. S. Department of Agriculture on qua- 

 ternary ammonium carbamates (5, 14, 16, 24) has shown that these 

 substances, the most readily available of which is Amo-1618 [(5-hy- 

 droxycarvacryl) trimethylammonium chloride, 1-piperidinecarboxyl- 

 ate], cause a striking inhibition of stem elongation in many plants. In 

 connection with our studies, it was of particular interest that GA re- 

 versed the inhibition induced by Amo-1618 in Chrysanthemum (6). 



Microscopic examination of several caulescent plants (i.e., plants 

 possessing elongate stems throughout their life), including Chrysan- 

 themum, Xanthium, and tomato, revealed a subapical zone of cell 

 division comparable in length to that of GA-treated rosette plants. 

 The relatively great number of mitotic figures observed in the sub- 

 apical regions suggested that in caulescent plants, too, the sub- 

 apical meristem plays an important role in shoot development (18). 

 Thus, it seemed a logical step to observe the action of Amo-1618 (and 

 GA) on subapical cell division in Chrysanthemum. 



U s 10* 



Fig. 5. Number and position of mitotic figures in the pith tissue of Chiysanthemum 

 per 60 /x median longitudinal section. Rooted cuttings were immersed for 24 hrs. 

 (continuous light) at 26° C. in one of the following solutions: A, water; B, G.\ 

 (100 mg/1); C, Am()-1618 (5-hydroxycarvacr\i)tiinict]iylannnonium chloride, 1- 

 piperidinecarboxylate, 100 mg/1); D, mixture of Amo-1618 and GA (both at 100 

 mg/1). The plants were transferred to soil and placed in long-day greenhouse con- 

 ditions, and 4 days later they were collected and examined. The plants of groups 

 E and F were immersed in Amo-1618 (same as C) and transferred to long-day 

 greenhouse conditions; 14 days later 200 ml. of water (E) or of GA (100 mg/1) (F) 

 were added to the soil in two doses of 100 ml. each on two successive days. Four 

 days after addition of water or GA to the soil, the plants were collected and exam- 

 ined. Each group contained four plants, and the diagrams are composites of six 

 median longitudinal sections (10 yx per section) taken from one of the treated plants. 

 Each dot represents a transverse mitotic figure. The boundaries of the vascu- 

 lai tissue and the lower limit of the apical meristem are indicated by solid lines. 



