LIBRARY 



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COMPARATIVE STUDIES ON THE GROWTH AND LIGH 

 SENSITIVITY OF GREEN AND ETIOLATED 

 PEA STEM SECTIONSi 



A. W. Galston and Ravindar Kaur 



Department of Botany 



Josiah Willard Gibbs Research Laboratory 



Yale University 



New Haven, Connecticut 



In recent years, the stem of the common garden pea (Pisum sativum 

 L.) has become one of the most frequently used objects in the study 

 of plant cell growth. Both the intact stem and small excised stem 

 sections of this plant show rapid and marked growth responses to 

 such environmental factors as light intensity, light quality, photo- 

 period, and temperature, and to such chemical influences as auxins, 

 gibberellins, cobaltous ion, and adenine. Originally (8, 18), stem 

 sections of the etiolated pea (3rd internode of 7 to 8-day-old plants) 

 were used exclusively in such studies, since their growth responses 

 to auxin paralleled in many respects those of the classical Avetia 

 coleoptile. More recently (2, 7, 10) , stem sections from light-grown 

 peas (the fifth internode of 14-day old plants) have been introduced 

 into plant physiological reasearch. Systematic investigation of the 

 biological and chemical properties of these two forms of the same 

 genetic material have revealed the existence of remarkable differences 

 in behavior which bear on our attempts to understand the nature of 

 growth hormone action and of the morphogenetic action of light. 

 For convenience in our later discussion, we have summarized the 

 major points of gross morphological and physiological difference be- 

 tween the light-grown and etiolated pea plants in Fig. 1 and in 

 Table 1. 



Numerous questions arise from this comparison which may be of 

 particular interest to the student of plant growth. These questions 

 include the following: (i) Why is the auxin optimum for growth 



' Aided bv giants from the National Science Foundation and the U.S. Public 

 Health Service. Miss Mary Lyons rendered expert technical assistance with som^ 

 of the section growth experiments. 



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