CROSS ADAPTATION; AN ALTERNATE APPROACH OF GENETIC ENGINEERING FOR SALINITY TOLERANCE IN RICE CELL LINE

Cell lines of Oryza sativa cv. Swat-1 incrementally adapted to osmotic (20% polyethylene glycol [PEG]) and ion toxicity (20 mM Lithium Chloride [LiCl]) stresses were exposed to 200 mM NaCl for two consecutive passages to study the cross tolerance mechanism. The patterns of response of adapted and unadapted cell lines to osmotic and ionic homeostasis to tolerate NaCl were greatly different. polyethylene glycol adapted cells line accumulated highest while LiCl adapted line accumulated lowest contents of Na+ and Na+/K+ ratios with corresponding higher indices of tolerance under NaCl stress than unadapted line. Adapted lines showed differential response to salt stress in accumulating proline with respect to duration of stress. Adaptation to PEG and LiCl was evident by appearance of six different polypeptides, among these four polypeptide bands 15, 17, 26 and 68 kDa were common, while, other two novel proteins 60 kDa, and 32 kDa were unique to PEG and LiCl adapted cell lines, respectively. None of these polypeptides were detectable in unadapted cell lines. At the molecular level PCR amplification results using six set of SSR primers revealed no polymorphism in adapted and unadapted cell lines. Failure of unadapted cell line to survive while significantly greater tolerance of both adapted cell lines during first and subsequent second passage to NaCl stress with six new polypeptide bands without any change at DNA level reveals that cross adaptation is the most reliable mechanisms for salinity tolerance and can be used as an alternate approach of genetic engineering against salt stress in rice.