Amelioration of salinity stress by exogenously applied spermidine or spermine in three varieties of indica rice differing in their level of salt tolerance.

We present here the comparative protective potentiality of exogenously applied polyamines (PAs), namely spermidine (Spd) and spermine (Spm), in mitigating NaCl toxicity and inducing short-term salinity tolerance in three indica rice varieties, namely M-1-48 (salt-sensitive), Nonabokra (salt-tolerant) and Gobindobhog (highly sensitive). The retardation in root length or shoot length and toxic Na(+) accumulation or K(+) loss, the considerable increment in malondialdehyde/H(2)O(2) accumulation or lipoxygenase activity, all of which were particularly noteworthy in M-1-48 and Gobindobhog during salinity stress, was appreciably reduced by co-treatment with Spd or Spm. Both the PAs also inhibited the extent of salt-induced protein carbonylation in all the varieties and enhanced protease activity, especially in Gobindobhog. The prevention of chlorophyll degradation was better with Spd in Nonabokra and Gobindobhog. While the salt-induced increase in anthocyanin or reducing sugar level was further prompted by Spd or Spm in all the varieties, the proline content was elevated by Spd particularly in Gobindobhog. During salinity stress, both the PAs were effective in lowering the putrescine accumulation in M-1-48 and Gobindobhog, and strikingly increasing the Spm level in all the varieties, the highest being in Gobindobhog. In addition, they enhanced the activity of peroxidases and compensated for the decreased catalase activity in all the varieties. Thus the two PAs could recuperate all the three varieties from salt-induced damages to different degrees. The salt injuries, encountered in M-1-48 and Gobindobhog, both of which showed greater susceptibility to salinity stress, were more pronouncedly alleviated and counteracted by the PAs, than the salt-tolerant Nonabokra. The reversal of inhibitory effect of salinity stress was conferred by preventing growth inhibition or various forms of cellular damages, maintaining proper K(+)/Na(+) balance or triggering the level of osmolytes and activity of antioxidant enzymes. Our communication offers a referenced evidence for an understanding of the mechanism by which higher PAs relieve the damages particularly in salt-sensitive rice varieties.