Polyethylene glycol treatment promotes metabolic events associated with maize callus morphogenic competence

Metabolic changes were studied, which accompanied the conversion of 6month old HiII maize non-regenerable (NR) calli into regenerable (R) calli when cultured for 63days with 10% polyethylene glycol (PEG) (3350MW) in culture medium. The conversion of 6month old NR to R callus morphotype caused by PEG application decreased cell wall contents in callus dry mass and changed cell wall phenolics making their profile similar to that of R callus by reduction of lignin and ester- and ether-bound phenolic concentrations, including p-coumaric acid and ester- and ether-bound diferulates and by increase of the ratios of ester- and ether-bound ferulic acid/coumaric acid and ferulic acid/diferulic acid in cell walls of NR callus. Some similar changes of cell wall phenolics caused by PEG application were also found in 48month old NR callus, that changed the morphology, but did not regenerate plants. However, there were no changes in the old callus in levels of total ester and ether-bound cell wall phenolics and substantially smaller decreases were found in ratios of ester- and ether-bound ferulic acid/coumaric acid and ferulic acid/diferulic acid, as well as in diferulate concentrations compared to young NR callus cultured with PEG. Remarkably, application of PEG also changed the primary metabolism of young NR callus tissues, so that they acquired metabolic features of highly regenerable callus. These data clearly suggest that PEG alters metabolism of NR calli, so they acquire biochemical characteristics of R calli, and that adaptive osmotic adjustments vary in different types of callus tissues.