Role of wheat trHb in nitric oxide scavenging

We examined the role of wheat truncated-hemoglobin (TatrHb) in nitric oxide (NO) scavenging in transgenic Arabidopsis plants by assessing the response to an NO donor/scavenger and salt stress. The degree of increase in Na⁺ and decrease in K⁺ levels in the transgenic plants were more than those in the wild-type plants, and the ratio of Na⁺ to K⁺ increased in the transgenic plants under salt stress. Endogenous NO increased dramatically in the salt-treated wild-type plants but not in the transgenic plants. Additionally, the maximum photosystem II quantum ratio of variable to maximum fluorescence (Fv/Fm) in transgenic plants decreased more significantly than that in the wild-type plants, indicating that the transgenic plants suffered more severe photosynthetic damage because of salt stress than that by the wild type. Similar results were observed in germination experiments by using Murashige and Skoog media containing 100 mM sodium chloride. The Fv/Fm decreased in the leaves of salt-treated transgenic plants, indicating that transgenic seeds were more sensitive to salt stress than that by the wild-type seeds. In addition, the negative effect on seed germination was more severe in transgenic plants than in the wild types under NaCl treatment conditions. The results support the hypothesis that plant trHb shares NO scavenging functions and characteristics with bacterial trHb.