A Comparison of 2,4-Dichlorophenoxyacetic Acid Metabolism in Cultured Soybean Cells and in Embryogenic Carrot Cells

Abstract

The removal or reduction in concentration of auxin is often a successful method for obtaining morphogenesis in cell cultures of higher plants, such as carrot, but not for soybean. For this reason, the metabolism of one auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), was compared in both carrot and soybean cells. Whereas soybean cells conjugated a high percentage of their 2,4-D to amino acids, carrot cells contained primarily free 2,4-D. Moreover, after long-term exposure to 2,4-D, carrot cells released much more 2,4-D upon transfer to 2,4-D-free (embryogenic) medium than did soybean cells. It appears that the retention of 2,4-D by soybean cells might interfere with subsequent morphogenesis. Because no impairment of 2,4-D efflux was found with short-term exposure to radiolabeled 2,4-D, it was concluded that 2,4-D retention in soybean cells might be due to a time-dependent, metabolic process. The conjugation of 2,4-D to amino acids was shown to be one such time-dependent process. Additionally, the release of 2,4-D from the cells was shown to be due primarily to a loss of free 2,4-D and not 2,4-D-amino acid conjugates. It seems that the greater retention of 2,4-D by soybean cells upon transfer to 2,4-D-free medium is due to greater formation of 2,4-D-amino acid conjugates.