Abstract:
Previous finding of chitosan-induced increase of silica bodies in Dendrobium orchid hints that chitosan may enhance silicon uptake, a beneficial element for plants. To prove that, plant responses to chitosan at cellular level are prerequisite. Thus, cell suspension culture has been established from callus culture of heterotroph Chenopodium rubrum L. Subsequently, early responses of cell suspension to three different concentrations of chitosan (O-80) were determined. Transient extracellular alkalinization occurred on a concentration-dependent manner. An increase of 0.30 pH units was detected with 5 and 10 ppm chitosan and 0.55 pH units with 100 ppm. In addition, acetic acid (solvent control) induced extracellular acidification. While extracellular protein release and cell mortality was not changed by 5 and 10 ppm chitosan, it was highly increased by 100 ppm. Based on extracellular pH and vitality, chitosan at 10 ppm was applied in 60-day long-term treatment with and without silicon supplementation. After 12 days, cells acidified the medium to pH 4.0, regardless of chitosan and acetic acid. Furthermore, extracellular silicon was decreased about 70% while intracellular silicon was increased 30% similarly in all treatments. During 60 days of cultivation, intracellular silicon varied between 0.15 to 0.22 mg g-1FW in all treatments similarly. It was also observed that cell mortality was slightly higher under high silicon condition, suggesting possible silicon toxicity. In total, the results suggest that chitosan does not enhance silicon uptake under investigated condition. Interestingly, C. rubrum cells increase silicon uptake when soluble silicon is available. Beneficial role of silicon in association with H+-mediated transport and cell starvation was discussed therein.
