Ejjcct of Gihberellin on Photosynthesis 



585 



of total sugars in the top is the same in the control and the treated 

 plants, but the content of reducing sugars is higher in the treated 

 plants than in the control. In the root, the contents of both reducing 

 and total sugars was decreased as a result of the GA treatment. 



Figure 7 shows the changes in the starch content. It is noticeable 

 that GA lowers the starch content in the top of the plants. In the 

 root, the starch content was almost nil in both the control and the 

 plants treated with GA. 



DISCUSSION 



The 10 to 18 per cent increase in photosynthetic activity of whole 

 plants about one week after treatment (Figures 2 and 3) may be ac- 

 counted for by any of the following possibilities: (1) photosynthetic ac- 

 tivity per unit leaf area is increased; (2) the activity per unit leaf area 

 remains unchanged, but, owing to the increase in leaf area by the 

 treatment, the amount of carbon dioxide fixed by the whole plant 

 increases; (3) the activity per unit leaf area decreases but the increase 

 in leaf area compensates for the decrease in activity; (4) the surface 

 area of organs other than the leaves, for instance, the leaf sheath in 

 rice plants, is increased by the treatment and the increase in photo- 

 synthetic activity of these organs accounts for the increased activity 

 of the whole plants; (5) the treatments affect the shapes of plants, in- 



TOTAL SUGARS 

 ROOT 



w A Control 

 » A GA-treated 



O 

 o 



Fiff. 6. 



4 6 



DAYS AFTER TREATMENT 



20 



16 



< 



_J 



d 



o 

 o 



12 Q: 



or 

 < 

 o 



CO 



o 



I- 



u. 

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I- 



10 Ld 



o 

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Changes in the sugar content of rice plants after treatment with gihberellin. 



