PEG-tolerant cell clones of chili pepper: Growth, osmotic potentials and solute accumulation

Abstract

Cell cultures of chili pepper (Capsicum annuum L.) were established from callus tissue inoculated in MS liquid medium supplemented with 6.25 μM 2,4-d and 0.44 μM BA. Cell clones were isolated by plating the cell suspension on filter paper discs supported by polyurethane foam that were bathed with culture medium containing 15% PEG. The cell clones T6 and T7 were chosen based on their characteristics of growth and friability. These cell clones were established as cell suspensions in the presence of 15% PEG and subsequently subcultured in increasing concentrations of osmoticum. By this approach the cell clones T7 and T6 were capable of growing in the presence of 20 and 25% PEG, respectively. The cell clone T7 was found to grow better in the presence of 5–10% PEG after a period of subculturing in the absence of osmoticum indicating that the tolerance trait was stable. The tolerant cell clones exhibited a 3 to 3.5-fold decrease in the osmotic potentials in comparison with the nonselected cells suggesting that osmotic adjustment occurred. K⁺ was the major contributing solute to the osmotic potential in all the cell cultures among those tested and was found to be higher in concentration in the PEG-tolerant clones (1.3–3 times higher than nonselected cells). Proline and glycine betaine levels showed a positive correlation with the degree of tolerance to water deficit in the PEG-tolerant cell clones. The levels of proline in the cell clone T7 subcultured in the absence of PEG in the culture medium decreased to values similar to those of nonselected cells, whereas the contents of glycine betaine in the same conditions were maintained at high levels.