688 



LIGHT AND LIFE 



Fig. 1. Morphological differences betwen etiolated (left) and light-grown 



(right) pea plants. 



of the green tissue a thousandfold higher than that for the etiolated 

 tissue? (ii) Why is the gibberellin effect on growth indejoendent of 

 auxin in etiolated tissue and auxin-dependent in green tissue? (iii) 

 Is there any physiological significance to the indole acetic acid (lAA) 

 oxidase inhibitor whose level in tissue is determined by the red 

 far-red photomorphogenic system? (12) (iv) Why are green stem 

 sections not inhibited in their growth by the red radiations which 

 are so effective on intact green plants and on etiolated sections? An- 

 swers to these and lelated questions can be obtained only Avhen 



TABLE 1 



,\ SlJMMAR^ OF Some Gross Morphological and Physiological Differknces 



Between Dark-grown and Light-grown Pea Stems 



Color 



Internode length 

 Internode width 

 Internode cross section 

 Nutritional habit 

 Sucrose optimum 

 Auxin (LA.A) optinnnn 

 Response to gibbcrellins 



Response to white light 

 Response to weak red light 

 lAA oxidase activity 

 lAA oxidase inhibitor 



Etiolated 

 white 

 very long 

 narrow 

 circular 

 heterotrophic 

 ca. 2% 

 ca. 10-" M 

 relatively large 

 independent of 

 inhibition 

 inhibition 

 high 

 absent or low 



aiixiii 



Light-grown 

 green 

 shorter 

 thicker 

 rectangular 



autotrophic or heterotrophic 

 ca. 1%; ca. 3% 

 > 10-* M 

 relatively small 

 dependent on auxin 

 |)r(>nu)tion 

 none 

 low 

 high 



