Modeling available 2,4-dichlorophenoxyacetic acid in a tissue culture medium containing activated carbon

Clonal propagation of high-value forest trees by somatic embryogenesis can help meet industry needs for uniform and high quality raw materials. Low embryogenic tissue initiation frequencies for loblolly pine (Pinus taeda L.) pose a limitation in work towards commercialization of this technology. At the time our research began most work on somatic embryo culture initiation in loblolly pine reported success in the range of 1-5%. Activated carbon (AC) has been reported to improve many tissue culture systems including embryogenic tissue initiation in Douglas-fir. To improve initiation frequencies in loblolly pine, the development of an AC-containing system was explored. In order to better understand the availability of 2,4-dichlorophenoxyacetic acid (2,4-D) in initiation medium, we tracked media surface concentrations of free or available 2,4-D. Media containing 1/2 modified P6 salts, 1.5% maltose, 2% myo-inositol, case amino acids, glutamine, vitamins, and 0.4% Gelrite were modified to include 0.625 - 2.5 g l(-1) of activated carbon (Sigma C-9157, acid washed) and 110 -440 mg l(-1) 2,4-D. Adsorption and availability of 2,4-D in AC-containing medium was tracked by C14 labeled 2,4-D present in surface moisture absorbed into filter paper. High correlations were found between -available 2,4-D and time when AC and initial 2,4-D concentrations were held constant, -available 2,4-D and AC concentration when initial added 2,4-D and time were held constant, and -available 2,4-D and initial 2,4-D when AC and time were held constant. All of these relationships were exponential, not linear. Multiple regression models inputting initial 2,4-D added to medium in mg l(-1), activated carbon added to medium in %, and time in days, were able to explain 85-88% of the variability in available 2,4-D. These models can be used to achieve target levels of available 2,4-D by adjustment of initial 2,4-D levels or AC content.