Translocation of Indole-3-acetic Acid-1′-14C and Tryptophan-1-14C in Seedlings of Phaseolus coccineus L. and Zea mays L.

Abstract

Indole-3-acetic acid-1′-¹⁴C (IAA-¹⁴C) and tryptophan-1-¹⁴C injected in small amounts into cotyledons of Phaseolus coccineus L. seedlings were found to be translocated acropetally into the epicotyls and young shoots. Similarly IAA-¹⁴C was translocated acropetally into coleoptiles of Zea mays following injection into the endosperms. Labeled metabolites of the injected compounds were also extractable from shoot tissue. However, evidence that IAA-¹⁴C itself was translocated acropetally was obtained by collection in agar blocks applied to cut surfaces of coleoptiles of injected seedlings. The acropetal translocation in Phaseolus was shown not to occur in the transpiration stream but in living tissue. Cotyledons of Phaseolus coccineus and Phaseolus vulgaris contain extensive vascular tissue. Tryptophan-¹⁴C was not actively translocated through excised segments of Phaseolus coccineus epicotyl and Zea mays coleoptile when supplied from donor agar blocks in concentrations as high as 100 μm. The small amount of tryptophan-¹⁴C which did reach receiver blocks when high concentrations were used may be accounted for by passive diffusion through the fluid-filled xylem vessels. Translocation of a non-toxic dye, Light Green SF Yellowish, through xylem vessels was found to occur when supplied from donor blocks placed acropetally or basipetally. Metabolism of the supplied tryptophan-¹⁴C by the tissue segments was shown to occur during the 3 to 6 hour translocation experiments. IAA-¹⁴C was transported in a strictly basipetal manner in both tissues. Only 1 labeled compound with an R_F value of IAA was found in receiver blocks. Composition of a simple green safelight suitable for work in plant physiology is described.