TAKESHI HAYASHI 



National Institute of Agricultural Sciences 

 Tokyo, Japan 



The Effect of GibbereULn Treatment on the 

 Photosynthetlc Activity of Plants 



It has been generally known that plants increase their height, leaf 

 area, and dry weight by treatment with gibberellin (GA). The in- 

 crease in dry weight may result from an increase in photosynthetlc 

 activity, or in the efficiency of utilizing photosynthetlc products. In 

 order to make this point clear, studies have been made (2, 4) in which 

 the fixation of radioactive C^^Oo by detached leaves was determined. 

 These results showed that GA does not distinctly affect COa-fixation 

 activity. 



It seemed desirable, however, to measure the COo-fixation activity 

 using whole plants; also in reference to the activity per unit leaf area, 

 it seemed preferable to use leaves attached to intact plants. 



In this report, the effects of GA treatment on the photosynthetlc 

 activity of whole plants and of attached leaves, also on the content 

 of some carbohydrates, are given. As test plants, tomato and rice 

 plants were used. 



EXPERIMENTAL METHODS 



Tomato plants, 'Sekai-ichi,' cultured in M^agner pots, and about 

 25 cm. in height, were used. GA in 50 p.p.m. aqueous solution was 

 sprayed onto the plants twice, at intervals of 3 days. In all experi- 

 ments, crystalline GA from the Kyowa Fermentation Industry Co., 

 Ltd. was used. 



Rice plants, 'Aichi-Asahi,' were first grown in a seed bed, and were 

 then transferred to Kasugai solutions when they were 20 cm. in height, 

 with six expanded leaves. The culture vessels were 500 ml. or one 1. 

 glass jars, and they were placed in the greenhouse. GA was added to 

 the culture solution at a concentration of 10 p.p.m. 



[579] 



