Distribution of natural hormones 



Further experiments were carried out in order to relate biological activity 

 of lAA to the actual amounts present in the extracts. Although this auxin is 

 concentrated mainly in strip 2 of the chromatogram, it occasionally spreads 

 into strip 1 and strip 3. In these experiments, therefore, the chromatograms 

 were divided up in a different manner. The zone of Rf 0-0-3 was cut 

 longitudinally into 3 similar strips, which were assayed separately, and the 

 lAA content of the sample was calculated from their mean value. By -using 

 known amounts of lAA it was possible to construct a calibration graph in 

 which the wheat cylinder extension growth, expressed as a percentage of the 

 control growth, was shown to give a linear relationship with the log of the 

 lAA concentration. 



Samples of germinating maize grains were taken at intervals of 12 hours as 

 in the preliminary experiment and biological assays of I AA were carried out 

 on extracts from different numbers of seeds at each sampling time. The 

 results of these experiments are presented in Table 1 and Figure 4. These show 



Table 1 

 Extracts from whole seeds 



Changes in lAA content of seeds during germination 



t Not significant. 



a rapid increase in the lAA content of the seed during the first 24 hours of 

 germination. The mean values obtained for 24 and 36 hour extracts are not 

 significantly different but a significant decrease is indicated between 36 

 and 48 hours. 



The results so far reported deal with total changes in the whole seed. An 

 experiment was next carried out in order to follow changes in the embryo and 

 endosperm separately. At each sampling time, the seeds were separated into 



35 



