Monitoring of cell wall modifications during callogenesis in Stylosanthes guianensis (Fabaceae) under salt stress conditions

Callogenesis was induced from Stylosanthes guianensis (Aubl.) Sw. cv. CIAT-184 hypocotyl explants cultured in the presence of different concentrations of NaCl. Whereas calluses formed at 50 mM NaCl did not show significant changes, concentrations in the range of 100-250 mM NaCl influenced callus formation and survival. The concentrations which reduced the callus formation and survival by 50 % with respect to the controls (I-50) were 190 and 225 mM NaCl, respectively. Callus growth was also affected being 160 mM NaCl the concentration that reduced the fresh weight gain in 50 %, in comparison to the control. The cell walls of calluses formed at higher NaCl concentrations showed a lower cellulose content, which was accompanied by an increase in protein, phenolics, and esters, as revealed by Fourier transform infrared spectroscopy. These overall cell wall modifications were accompanied by the formation of cell wall appositions enriched with homogalacturonan and rhamnogalacturonan components, and also with an increase of arabinogalactan proteins in cell walls. These results evidence the ability of cells to adjust the cell wall composition under salt stress conditions, as part of the strategy to sustain their growth in such environment.