The Uptake and Fractional Distribution of Differentially Labeled Indoleacetic Acid in Light Grown Stems

The uptake of exogenously applied indoleacetic acid (IAA) by light grown stems of bean (Phaseolus vulgaris L. cv. Red kidney) and pea (Pisum sativum L. cv. Alaska) was examined. The IAA was labeled in the 1 and 2 side chain positions with ¹⁴C and the 5 ring position with ³H. The distribution of label in the sections was analyzed by recording the elution into water, ethanol and 1.0 N NaOH, and the amount in the insoluble residue also recorded. Total uptake consisted of a rapid uptake for about 1 h followed by continued uptake at a slower rate for 24 h to give a radioactive concentration in the tissues four to five times, that of the external solution. Most of the radioactivity was initially extractable by water, later by ethanol. With IAA-2-¹⁴C there was a slow increase in radioactivity in NaOH and residue fractions but with IAA-1-¹⁴C most of the radioactivity was present in insoluble residue at times longer than 3 h. From the different residue patterns estimates of the extent of decarboxylation of the IAA were made. The radioactivity in the tissues was largely IAA after 1 h and the content increased until 6 h but there after there was little further increase. The water fraction initially contained the most IAA but by 24 h most IAA was found in the NaOH fraction in bean and the ethanol fraction in pea. The NaOH fraction was the only fraction in which the IAA content continually increased.