Gibberellin-Auxin Interaction and Metabolic Basis 



613 



daily with a nutrient solution composed of 120 g. Hyponex (Hydro- 

 ponics Chemicals Co., Copley, Ohio) per 100 1. tap water. Subapical 

 5 mm. stem sections were obtained from 14- to 18-day-old plants with 

 a double-bladed cutting tool. Green sections were grown under high 

 intensity (ca. 1,200 foot candles) fluorescent light in a medium con- 

 taining sucrose and buffer as above, and GA and lAA, where indi- 

 cated, at 10-4 ][/[ These conditions have recently been determined in 

 our laboratories to be optimal for the growth of such sections, but 

 space limitations preclude detailed description of such experiments 

 here. Measurement of the growth of green sections was made by the 

 same methods as detailed above. 



Results 



Typical results with etiolated peas are shown in Table 1, which 

 gives the growth increments produced by lAA and GA alone, and the 

 two together, when supplied to (a) sections from completely etiolated 

 plants, (b) sections from etiolated plants exposed to weak red light 

 24 hrs. prior to harvest, (c) etiolated sections pretreated with GA or 

 control media for 30 min. and then transferred to growth solution 

 containing or lacking lAA, and (d) sections from 100 mm. long etio- 

 lated epicotyls treated basally for 30 min. with GA, then excised 

 and placed in growth solutions containing lAA. In the latter two se- 

 ries the pretreatment with GA followed previously published methods 

 (7) of immersion in 1 per cent sucrose and buffer -f 10 ^ M GA for 

 the indicated period. The completely etiolated sections show a large 

 response to GA, a larger response to lAA, and less than additive effects 

 of the two compounds together. Red light pretreatment reduces the 

 endogenous growth and response to auxin, as previously reported (4), 

 as well as the response to GA. GA pretreatment, either to sections or 



Table 1 . Absence of GA-IAA synergism in etiolated pea epicotyl sections derived 

 from plants treated in various ways. All sections initially 5 mm. long. All figures are 

 averages of two closely checking means, each derived from ten sections growing in a 

 single dish. Data in lower section of table represent a separate experiment. 



