Sterile solution culture techniques for aluminum toxicity studies involving organic acids

Abstract

Microbial degradation of low molecular weight organic acids can be a serious source of error in solution culture experiments concerned with the protection of plant roots by these compounds against aluminum (Al) toxicity. Under normal glasshouse conditions, the problem was not solved by sterilisation of the various components of the solution culture system and surface sterilisation of the soybean and mungbean seeds. Of four water soluble antibiotics tested, streptomycin, rifampicin, and trimethoprim were phytotoxic at concentrations ≥ 50 mg/L; cefotaxime, while not phytotoxic up to 150 mg/L, gave poor control of microbial growth in 2‐day root elongation tests with mungbean. However, addition of 30 mg/L cefotaxime plus 20 mg/L trimethoprim at planting and a further 30 mg/L cefotaxime after one day was effective in controlling microbial numbers and preventing significant loss of added citrate to the solutions. At these concentrations the antibiotics were non‐phytotoxic and appeared not to cause any complexation of Al. Use of the method showed that citrate, L‐malate, and oxalate were highly effective detoxifiers of Al in solution.