Rice can acclimate to lethal level of salinity by pretreatment with sublethal level of salinity through osmotic adjustment

Abstract

The physiological ability to adapt for various environmental changes is known as acclima- tion. When exposed to sublethal level of stress, plants develop the ability to withstand severe stress, as ac- quired tolerance. The present study was conducted to explicate the physiological basis of acquired tolerance in rice. Rice seedlings (variety IR 20) were grown in half strength Hoagland solution, and after 22nd day, they were kept in half strength Hoagland solution containing 50 mM NaCl (sublethal dose) for 7 days followed by half strength Hoagland solution contain- ing 100 mM NaCl (lethal dose) for another 7 days. The non-pretreated 29 days old rice seedlings main- tained in half strength Hoagland solution were directly transferred to half strength Hoagland solution con- taining 100 mM NaCl (lethal dose) solution for 7 days. The control plants were maintained in half strength Hoagland solution without NaCl. Various morphological and physiological parameters were recorded on 29th and 36th days old seedlings from control, pretreated and non-pretreated plants. The re- sults revealed significant reduction in growth param- eters (shoot length, root length, leaf area and total dry matter production) of non-pretreated plants below that of pretreated plants. The pretreated plants showed increased values to the extreme of 19.8 per cent in leaf water potential (ww), 9 per cent in relative water content (RWC), 26 per cent in photosynthetic rate (PN), 28 per cent in leaf stomatal conductance, and 47 per cent in chlorophyll a over non-pretreated plants. The same trend was also observed in chlorophyll a/b ratio (6.6%) and Fv/Fm ratio (19.3%). However, a reverse trend was seen in Fo value. The pretreated plants showed improved ionic regulation as evident from low Na + ,C l ) and high K + contents, which is attributed to enhanced plant water status and photo- synthesis. Both pretreated and non-pretreated plants had higher contents of osmolytes viz., sucrose, leaf soluble sugars and proline contents than control plants. However, starch content revealed an inverse trend. Therefore, the present study reveals that rice can acclimate to lethal dose of salinity stress by pre- treatment with sublethal dose of NaCl.