PHYSIOLOGICAL AND MORPHOLOGICAL EFFECTS 



OF GIBBERELLIC ACID ON EPICOTYL 



DORMANCY OF TREE PEONY ^ 



LELA V. BARTON and CLYDE CHANDLER 



Boyce Thompson Institute for Plant Research, Inc., Yonkers, 



New York 



Gibberellic acid has been found to promote the growth of dormant 

 epicotyls of tree peony replacing the need for low-temperature pre- 

 treatment for the production of green shoots in the greenhouse. Appli- 

 cation of 1, 10, or 100 ixo to the hypocotyl of the germinated seed be- 

 fore planting in soil caused the emergence of green shoots above 

 ground in 3 weeks or less. Most rapid development of the epicotyl fol- 

 Towed treatment with 100 /^g gibberellic acid, but more normal growth 

 resulted from the lower dosages. This is the only chemical which has 

 been found to break epicotyl dormancy of tree peony. 



Morphological studies have shown that differentiation of epicotyl- 

 edonary tissues and elongation of the epicotyl axis proceeds slowly in 

 untreated seedlings in soil in the greenhouse. After application of 

 gibberellic acid, however, both differentiation and elongation were 

 rapid, as shown by microscopic examination of sectioned material. 

 Elongation of the epicotyl induced by gibberellic acid or by a period 

 of 8 weeks at 5°C was characteristic of seedlings which were capable 

 of green-shoot production in soil in the greenhouse. Such elongation 

 did not occur in untreated seedlings that failed to produce green shoots. 

 Elongation of the epicotyl axis is due to an increase in cell size and 

 cell number. 



1 Complete paper published in Contrihs. Boyce Thompson Inst., 19, 201-14 

 (1957). 



223 



