Metabolic effects of glyphosate change the capacity of maize culture to regenerate plants.

Since the presence of glyphosate in maize tissue cultures of proprietary line L2 was very detrimental to plant regeneration, we determined metabolic changes associated with the glyphosate effects on plant regeneration in maize cultures. The polar fraction composition and soluble and cell-wall-bound phenolics were analyzed in the regenerable (R) and non-regenerable (NR) calluses of maize line L2. The tissues with high regeneration capacity had low sugar and 4-aminobutyric acid (GABA) concentrations and increased concentrations of most amino acids, polyamines and indole-3-butenol in the soluble polar fraction and higher ferulic acid/coumaric acid and ferulic acid/diferulic acid ratios and higher levels of the predominant G (guaiacyl) units in the cell wall fraction compared with NR calluses as was found before with H99 and HiII maize R and NR tissues, indicating an association of these metabolites with the capacity of maize cultured tissue to regenerate plants. We also found that di-coumaroyl spermidine and coumaroyl-feruoyl spermidine are present in the soluble fraction of L2 R tissues and are practically absent in NR tissues. However, we did not see such differences in HiII and H99 samples, which indicate that these are genotypic features not related to the capacity to regenerate plants in maize tissue cultures. Glyphosate treatment caused the accumulation of shikimic and quinic acids (not detected in untreated samples) in R and NR calluses (with higher levels found in R tissues) and also decreased the FA/diFA ratio in cell wall phenolics, polyamine and amino acid levels, and increased sugar concentrations in the R L2 tissues, indicating a metabolic shift of R callus to NR tissues.