Effect of Nitric Oxide on Proline Metabolism in Cucumber Seedlings under Salinity Stress

Abstract

<jats:p>Nitric oxide (NO), an endogenous signaling molecule in plants and animals, mediates responses to abiotic and biotic stresses. This study was conducted in a nutrient solution to investigate 1) the effects of exogenous sodium nitroprusside (SNP), an NO donor, on free proline (Pro) and protein content; and 2) the enzymes involved in Pro metabolism [pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (PDH)] in cucumber (<jats:italic>Cucumis sativus</jats:italic>) seedling leaves and roots under NaCl stress. The results showed that the increases in free Pro and protein were significantly higher in the 50 m<jats:sc>m</jats:sc> NaCl solution but highly significant with the addition of 100 μM SNP to the 50 m<jats:sc>m</jats:sc> NaCl solution for the entire treatment period. Moreover, leaves maintained higher levels of free Pro and protein content than roots throughout the experiments. The P5CS activity increased in the saline treatment compared with the control, and this increase was greater in the 50 m<jats:sc>m</jats:sc> NaCl + 100 μM SNP solution than in the other treatments. On the other hand, the PDH activity was inhibited under NaCl stress but the reduction in activity was greater in the 50 m<jats:sc>m</jats:sc> NaCl + 100 μM SNP solution than in the others. These findings suggest that Pro metabolism was significantly altered during the exogenously applied NO under salt stress and that this alteration prompted the accumulation of higher levels of free Pro, which, in turn, maintained the turgor in the cucumber seedlings and helped protect them from salt stress. Moreover, the toxic effects generated by 50 m<jats:sc>m</jats:sc> NaCl were partially overcome by the application of NO, which could be used as a potential growth regulator to improve plant salinity tolerance. Therefore, it was concluded that NO could alleviate salinity damage in cucumber seedlings by regulating Pro metabolism. Overall, the adverse effects of salt stress could be lessened by the exogenous application of NO to cucumber seedlings.</jats:p>

Isolation and Characterization of a Class III Peroxidase cDNA from Cucumber under Salt Stress

“…1). This result is in agreement with the previous reports regarding salt-treated cucumbers (Du et al, 2010a;Duan et al, 2008;Fan et al, 2012;Shi et al, 2007). Duan et al (2008) suggested that cucumber seedlings most likely increase the protein level of antioxidant enzymes and the content of osmoticants to enhance resistance to salinity.…”

“…The physiological responses of cucumber seedlings to salt stress have been well characterized. Specifically, salt stress destroyed the steady-state balance of reactive oxygen species (ROS) in cucumber seedlings, resulting in the loss of relative water content and net photosynthetic rates as well as a decrease in plant growth rates (Du et al, 2010a;Duan et al, 2008;Fan et al, 2012;Shi et al, 2007). Therefore, studies on salt stress are important to further understand the developmental mechanisms affected by salt for cucumber production.…”

Exogenously Applied Nitric Oxide Enhances Salt Tolerance in Rice (Oryza sativa L.) at Seedling Stage

“…The increased transcript level of the proline biosynthesis gene (OsP5CS2) in NO-pretreated seedlings of the susceptible genotype under saline conditions, indicates the role of NO in the production of proline, which plays a significant role in counteracting salt-induced osmotic stress [64]. NO-induced proline accumulation in response to salinity in other crop species-such as wheat [53], cabbage [52], chickpea [46], and cucumber [54]-are in agreement with the present study.…”

“…The other ameliorating effect of NO on abiotic stress is through the metabolism and production of osmolytes in plants [51]. NO triggered biosynthesis and accumulation of proline content was reported in wheat, cucumber, and Chinese cabbage against salt stress [52][53][54]. Therefore, considering the multifaceted role of NO under stress conditions in different species, this study was designed to evaluate the mitigation effect of NO on salt stress in susceptible and tolerant rice genotypes with regard to gene modulations and phenotypic response.…”

NO accumulation alleviates H2O2‐dependent oxidative damage induced by Ca(NO3)2 stress in the leaves of pumpkin‐grafted cucumber seedlings

“…However, the role of NO and the relationship between NO and H 2 O 2 , in rootstock‐grafted (Rs‐G) cucumber seedlings in response to salt stress‐induced oxidative damage is still unclear. In a previous study, it was demonstrated that application of exogenous NO reduced the harmful effects of salinity on cucumber seedlings (Fan et al ). In the present study, we used NO scavenger and inhibitors [2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethy‐limidazoline‐1‐oxyl‐3‐oxide (cPTIO), tungstate and N w ‐Nitro‐ l ‐Arg methyl ester hydrochloride ( l ‐NAME)] as well as H 2 O 2 scavenger and inhibitor (DMUT and DPI) to investigate the relationship between NO and H 2 O 2 in grafted cucumber plants under Ca(NO 3 ) 2 stress.…”