Comparative phytotoxicity of the fumonisins, AAL-toxin and yeast sphingolipids in Lemna minor L. (Duckweed)

Fumonisin B1 and AAL-toxin, both of which contain sphingolipid-like substituents, are water-soluble metabolites of Fusarium moniliforme and Alternaria alternata, respectively. These two toxins were compared to each other and to tetraacetylphytosphingosine (TAPS) and triacetyldihydrosphingosine (TADS) for effects on chlorophyll production and growth in Lemna minor L. (duckweed). Fumonisin B1 (0.7 mug), TAPS, and TADS all produced parallel effects on growth rate and chlorophyll content; however, FB1 did so at a 33-fold lower concentration. The AAL-toxin at 0.7 mug affects chlorophyll content more than plant growth (36% versus 73%, respectively), whereas at 3.3 mug concentration, the growth rate was less than 50% and chlorophyll content was reduced by 80%. By contrast, the hydrolysis product of FB1 that does not contain the tricarballylic acid (TCA) substituent is 23 times less active, which suggests that this component somehow enhances activity. The yeast sphingolipids are completely acetylated and do not contain TCA groups but also affect chlorophyll content and growth rate of duckweed. However the effect was substantially less than with AAL-toxin and FB1, which contain one and two TCA groups, respectively.