The Role Of Exogenous Nitric Oxide Donor SNP In Modulating Root Growth And Oxidative Damage In Wheat (Triticum Aestivum L.) Seedlings Under Salt Stress

Nitric oxide (NO) was first described in mammals, where it plays variable functions ranging from dilation of blood vessels to neurotransmission and immune response. More recently, a growing body of evidence indicated that NO also played important roles in plants, and its involvement as a stress signal in adaptive response and mediating growth regulation processes were reported. However, the function of NO on plant root growth processes under salt stress is still unclear. In this paper, the relationship between NO and ROS in the process of wheat root growth and effect of NO on oxidative damage were surveyed.Treatment with different concentration of NaCl enhanced H2O2 level in wheat root tissues. At the same time, the root growth was inhibited. When the roots of wheat treated with exogenous NO alone, the results indicated that low concentration of SNP could promote root growth and high concentration inhibited root growth.Application of lower concentration of SNP (0.01, 0.05 and 0.1 mmol/L) , an NO donor, obviously alleviated the root growth inhibition effect of salt on root elongation at salt concentrations around 150 mmol/L, but was ineffective when NaCl concentration was at 300 mmol/L or higher. It was most effective at 0.05-0.1 mmol/L. Among them, the effect of 0.05 mmol/L SNP treatment was the most obvious. On the contrary, higher concentration of SNP (1,3 and 5 mmol/L ) displayed significant toxic effect to root growth. However, it was noticeable that when the concentrations of NaCl were above 300 mmol/L, SNP with various .concentrations all showed no apparent effects. NO, HiOi and Ca2+ were putative signaling molecular in plants. The relationship and function of them in wheat roots growth were investigated. Trie result exhibited that Ca2+ played a key role in wheat roots growth.When H2O2 in wheat roots was scavenged by DMTU, a scavenger of H2O2, the effects of Ca2+ on root growth could be inhibited. LaCl3, an Ca2+ channel inhibitor, depressed the rootelongation of wheat seedlings under salt stress. But, treated with LaCl3 puls H2O2 could not alleaviated the inhibitory effect of root elongation of wheat seedlings exposed to salt stress. This indicated that H2O2 might be in the upsteam of Ca2+ signaling and regulate Ca2+ fluxes.Furthermore, when wheat seedling roots were treated with 150 mmol/L salt stress in combination with 0.05 mmol/L SNP and NO scavenger (Hemoglobin, Hb), NO3-/NO2- and K3Fe(CN)6, respectively, activities of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) were enhanced to some extent. While, the generation rate of O2, the accumulation of MDA and H2O2 were also alleviated. On the other hands, the DNA laddering was also observed when wheat seedling roots exposed to 150 mmol/L NaCl for 6 d, which further suggested that salt stress might induce oxidative damage in root-tips. In combination with hemoglobin, an NO scavenger, and NO2-/NO3- and K3Fe(CN)6 as controls, results showed that NO could block DNA ladders. Taken together, above results suggested that it was NO rather than any substances playing an important role in protecting root-tip cells of wheat seedling from oxidative damage caused by salt stress.