Growth of Carrot Cell Suspension Cultures in Medium Containing Amino Acid Conjugates of Indoleacetic Acid

Abstract

Suspension cultures of carrot cells ( Daucus carota L. cv. Danvers) are routinely maintained in medium containing 2,4-dichlorophenoxyacetic acid (2,4-D). When transferred to medium containing indoleacetic acid (IAA), the cells require twenty-fold higher concentrations of IAA for comparable growth. We tested eleven IAA-amino acid conjugates as auxin substitutes, and none was as effective as IAA. The cells took up more than 50 % of the IAA and IAA-leucine in less than 1 h, and more than 90 % in 8 h. After 8 h of growth in IAA, only 10 % of the radioactivity within the cells was in IAA, 45 % was in IAA-aspartate, and the rest was in breakdown products of IAA. IAA-leucine was immediately hydrolyzed to release IAA. The IAA was metabolized and IAA-aspartate was the primary end product. IAA-aspartate was taken up at much slower rates, and after 8 h, less than 10 % was in the cell. These results show that cell suspension cultures of carrot, unlike other culture systems, contain high esterase activity towards a wide range of IAA conjugates. The conjugates are hydrolyzed so quickly that they are unable to function as slow release forms of IAA and, hence, are not suitable replacements for 2,4-D in the medium.