GROWTH SUBSTANCES-RED LIGHT INTERACTIONS 



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Fig. 5. Elongation of 8-mm sections cut 4 mm from apex of red-grown 

 plants as affected by red light (R) treatment or 3 X IQ-^M kinetin (K) 

 in the presence or absence of IQ-^M lAA (I). (A, exp. 5-17-57; B. exp. 

 6-26-57.) 



No red light inhibition was observed in sections from red-grown 

 plants at any concentration of lAA (cf. Fig. 5A). 



While relatively low lAA levels do not affect the red light inhibition, 

 the data in Fig. 6 show that sufficiently high concentrations prevent 

 both red and FR effects. The lower pair of lines represents the elonga- 

 tion of sections from dark-grown plants, with or without red treatment. 

 While a significant red inhibition was present at 10 -'M lAA, none 

 was observed at the higher levels. Similarly, the upper pair of lines 

 indicates that FR promotion of elongation is still in evidence at \0~''M 

 lAA, but not at 10"^. 



Comparison of Effects of Kinetin and of Red Treatment 



Several reports have appeared (Miller, 1956; Scott and Liverman, 

 1956; Hillman. 1957) showing that the effects of kinetin (6-furfuryl- 

 aminopurine) frequently resemble those of red light. It was thus of 

 interest to compare kinetin and red light effects on internode sections. 

 Kinetin inhibited elongation at concentrations as low as 10~''M. 

 When tested against endogenous growth, no difference was apparent 

 between its effects on sections from dark-grown plants and sections 

 from red-grown plants. Figure 5B shows that kinetin, unlike red light, 

 strongly inhibited lAA-induced elongation in sections from red-grown 

 plants, although the concentration used (3 X 10"^M), like the red 

 light (cf. Fig. 5A) hardly affected endogenous growth. 



