Effects of nitric oxide on some physicochemical characteristics of NaCl salinity stress tolerance in Pyrodwarf and OHF69 pear roostocks

Salinity is a significant restriction for the cultivation of horticultural crops. Pear trees are generally classified as salt-sensitive. Nitric oxide (NO) is an endogenous signaling molecule that plays a crucial role in various physiological processes, including salinity stress. Variations in endogenous NO levels and or exogenous NO application has shown to regulate abiotic stress resistance suggesting that this approach may contribute in enhancing crop production under stress conditions. In this research, the effects of NO treatment on some parameters NaCl stress tolerance were investigated in Pyrodwarf and OHF69 pear (Pyrus communis) rootstocks in order to evaluate the tolerance of Pyrodwarf and OHF69 pear rootstocks under NaCl stress.

The experiment was conducted in the research greenhouse of University of Tabriz in 2018. The experiment was factorial based on a completely randomized design with three replications. Sodium nitroprusside as a NO donor (0, 0.1, 0.5 and 1 mM) was applied to pear rootstocks under NaCl stress (0, 50, 100 and 150 mM) through the root system. NO treatments were applied at four levels along with nutrient solution through the root with the interval of 2 weeks. At the end of the experiment, the parameters of the height increment, relative water content (RWC), malondialdehyde content, proline, H2O2 and the concentration of Na+ and K+ of the leaves were evaluated. Data analysis was done using SPSS, version 22, and mean comparison was performed using the Duncan test at a 5% level.

The NO application significantly increased height of pear rootstocks, RWC and proline of leaves, and decreased malondialdehyde, H2O2 content of leaves both OHF69 and Pyrodwarf rootstocks exposed to NaCl stress. These results are in agreement with previous studies in citrus (Tanou et al., 2012) and apple (Aras et al., 2020). NO-treated plants showed a higher amount in both K+ concentration and K+/Na+ ratio and lower Na+ concentration. It is important to maintain the balance of nutrients in plant growth under salinity, and SNP treatment reduced the concentration of Na+ in plants exposed to salinity stress in citrus (Khoshbakht et al., 2018) and strawberry (Kaya et al., 2019). OHF69 rootstocks had higher amounts in relative water content, proline and K+/Na+ ratio than pyrodwarf rootstocks, and also showed lower content of H2O2 and Na+ concentration. The results of this experiment indicate that 1mM NO application mitigated the damages of NaCl stress. Moreover, OHF69 rootstocks at all salinity levels of NaCl indicated a higher relative tolerance compared to Pyrodwarf.

According to the results, NO application mitigated the negative effects of NaCl stress. Also, it is considerable that treated plants with 1 mM SNP under 50 mM NaCl stress had no significant difference compared to the control plants, which can be considered to stress tolerance under short-term salinity condition, and OHF69 rootstocks at all salinity levels of NaCl showed a higher relative tolerance compared to Pyrodwarf.Keywords: H2O2, proline, Pyrus communis, sodium nitroprusside, stress