lAA OXIDASE INHIBITOR AND MORPHOGENESIS 



147 



Several experiments performed with excised leaflets revealed that 

 they are capable of manifesting these same variations in inhibitor con- 

 tent as a result of light-dark alterations. In Fig. 3 are presented data 

 from a typical experiment, showing a rise in inhibitor level in the first 



>- 



I 2 



HOURS OF 



3 4 



DARKNESS 



Fig. 3. The effect of incubation in darkness of leaflets excised from 

 pea plants previously grown in continuous light on their content of lAA 

 oxidase inhibitor. 



hour or two of darkness followed by a fall after 4 hr. It is also note- 

 worthy that the temporary rise is largely reversed by transferring the 

 dark-exposed leaf discs to light. 



Comparative Inhibitor Content of Tall and Dwarf Peas. The oc- 

 currence of a gradient of lAA oxidase inhibitor down the stem, to- 

 gether with variation in inhibitor content with light-dark alterations 

 (see also Hillman and Galston, 1957) suggested a possible role for 

 this substance in normal growth regulation. To test this possibility, 

 further comparisons were made of the inhibitor content of tall 

 (Alaska) and dwarf (Laurel) pea seedlings grown in the light. In both 

 instances, 14-day-old plants were used, all having been grown under 

 24-hr photoperiods and at 17°C. 



Individual leaflets of the youngest expanded leaf (fifth node) were 

 harvested, wrapped in filter paper, and placed in the bottom of an 18 



