SALT TOLERANCE IN COTTON CALLUS TISSUE TRANSFORMED WITH ASCORBATEPEROXIDASE, GLUTATHIONE REDUCTASE, AND SUPEROXIDE DISMUTASE

摘要

Exposure to high levels of NaCl has been shown to induce an oxidative stress in cotton (Gossypium hirsutum) callus tissue.In addition, it has been demonstrated that cotton cell lines which are capable of up-regulating their antioxidant enzyme activitiesare more tolerant to NaCl stress than cell lines which do not increase the activities of these enzymes. This experimentwas designed to determine if cotton callus tissue which had been genetically transformed with cDNA which encodes for antioxidantenzymes was more tolerant to NaCl stress than a NaCl-sensitive cell line and a NaCl-tolerant cell line selected togrow on elevated NaCl levels. Callus from a NaCl-sensitive cell line, a NaCl-tolerant cell line manually selected to grow athigher NaCl concentrations, a transgenic cell line transformed with glutathione reductase (GR+), a transgenic cell line transformedwith ascorbate peroxidase (APX+), and a transgenic cell line transformed with superoxide dismutase (SOD+) wasgrown on media amended with 0, 150 mM NaCl, or 250 mM NaCl. After 28 days, the callus was harvested, weighed, andanalyzed for catalase, peroxidase, GR, APX, and SOD activities. The growth studies showed that the transgenic cell linesgrew better at both the 0 and the 150 mM NaCl levels than did either the NaCl-sensitive or the NaCl-tolerant cell lines. At the250 mM NaCl level, the transgenic cell lines were more tolerant than the NaCl-sensitive cell line which died before the endof 28 days; however, the NaCl-tolerant cell line exhibited significantly more NaCl tolerance than any of the transgenics. Ananalysis of the antioxidant enzymes revealed that while each of the transgenics over expressed its respective antioxidant enzyme,the activities of the other enzymes remained relatively low, and in some cases the activity was actually lower than theactivity expressed by the NaCl-sensitive cell line. On the other hand, the NaCl-tolerant cell line expressed significantlyhigher activities of all five antioxidant enzymes when grown on high NaCl than did the NaCl-sensitive cell line. These datasuggest that in order to achieve a significant level of NaCl tolerance, the activities of several of the antioxidant enzyme mustbe up-regulated simultaneously.