Auxin metabolism and transport in an embryogenic cell line of Daucus carota L.

In this paper we analysed the endogenous IAA levels in carrot cell cultures and in cell culture medium. Free IAA and its conjugates (esters and amides ) were measured in cell cultures exposed to different concentrations of 2,4 -D (nil, 2,3 and 92 mu mol/L). The three culture conditions determine diffe rent physiological conditions of the cell cultures: somatic embryogenesis, unorganised growth and growth under stress, respectively. The results indic ate that these two types of IAA conjugates account for 60-70 % of total IAA and buffer the variations of free IAA in a sequential manner. Free IAA is in a steady state relationship with the eater conjugates and th e increased synthesis of IAA is initially buffered by IAA-amide. When a cer tain threshold (750 ng/g) is reached inside the cell by the amide, further increments are buffered by ester IAA. Another result coming from this analysis is that the presence of tryptophan alone in the culture medium is sufficient to sustain, metabolically as wel l as physiologically, the conditions of proliferation, shifting the state o f the cell culture from somatic embryogenesis to unorganised growth.