Physiology of acclimation to salinity stress in pea (Pisum sativum)

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Pea (Pisum sativum L.) seedlings were grown in half strength Hoagland solution and exposed to 0, 10, 25mM NaCl and 2.5% PEG 6000 for 1 week (pre-treatment). Thereafter plants were exposed to 0 and 80mM NaCl for 2 weeks (main treatment). The control plants were maintained in half strength Hoagland solution without NaCl. Various physiological parameters were recorded from control, pretreated and non-pretreated plants. There was no negative effect of the pre-treatments on growth (total fresh and dry matter production), and plants pre-treated with 10mM NaCl had biomass accumulation equal to control plants. The beneficial effect of salt acclimation was also evident in the prevention of K+ leakage and Na+ accumulation, primary in roots, suggesting that here the physiological processes play the major role. 2.5% PEG 6000 was not as efficient as salt in enhancing salt tolerance and acclimation appears to be more related to ion-specific rather than osmotic component of stress. We also recorded an increase of the xylem K/Na in the salt acclimated plants. Therefore, the present study reveals that short-term exposure of the glycophyte P. sativum species activates a set of physiological adjustments enabling the plants to withstand severe saline conditions, and while acclimation takes place primary in the root tissues, control of xylem ion loading and efficient Na+ sequestration in mesophyll cells are also important components of this process.