Analysis of NaCl tolerance in calli and regerants of unadapted and LiCl adapted lines of rice (Oryza sativa L.)

Abstract

In this study the response of calli lines of Oryza sativa L. cv.Swat-1 adapted to ion specific stress (25mM LiCl) was investigated to elucidate the underlying mechanisms of adaptations at the cellular level and their stability at regenerant stage. The physiological and biochemical parameters revealed that adaptation caused a decrease in proline, Na+, Na+/K+ratio, protein content and regeneration capability, while K+,Ca++and Mg++concentration enhanced. Exposure of cell lines to interactive effect of NaCl and CaCl2 showed that high calcium reduced the Na+ toxic effect on relative growth rates of both the cell lines with a concomitant increase in K+, Ca++ and Mg++ content respectively. While total sugar and proline contents of unadapted line increased and of adapted line decreased. Adaptation caused the appearance of one new protein band of about 67 kDa which remained stable under 200mM NaCl stress. While this band slightly appeared in unadapted line with degradation of other low molecular weight protein e.g. 17, 19 and 20 kDa. High calcium chloride caused upregulation of 67 kDa band with restoration of the damaged proteins except 17 kDa band. Regenerants and plantlets of adapted line showed excessive accumulation of osmolytes (sugar, proline) compared to accumulation in unadapted line. On the other hand the proteins’ banding pattern of regenerants was found to be similar to their respective lines. Interestingly 67 kDa band disappeared from the shoot of regenerated plantlets but was present in roots. No polymorphism was detected when 17 SSR markers related to Saltol region , 6 SSR markers for Na+/K+ ratios and one each for Na+/H+ antiport K+/Na+ symporter activity at plasma membrane was used. Transcriptional and translational inhibitors studies showed that changes due to adaptation were at translational/software level. This study reveals that the adaptation to ionic stress and supplemental CaCl2 under NaCl stress works on a similar principal of cellular homeostasis regain and adaptation at the cellular level is transferable (stable) to complete plant level.