BackgroundThe aim of this experiment was to analyze the alleviation mechanism of exogenous salicylic acid (SA) and sodium nitroprusside (SNP, a nitric oxide donor) on peanut seedlings under Fe deficiency. The effects of SA and SNP on iron uptake and availability, ions balance and oxidant damage were studied with foliar application of exogenous 1.0 mM SA (SA) or 2.5 mM SNP (SNP) or 0.5 mM SA+1.25 mM SNP [1/2(SA+SNP)] or 1.0 mM SA+2.5 mM SNP (SA+SNP).ResultsThe results showed that after 21 days treatment, the peanut seedlings growing under iron deficiency conditions exhibited leaf interveinal chlorosis, and this iron-deficiency induced symptom was prevented by foliar application of SA, SNP, 1/2 (SA+SNP), especially SA+SNP. The increased contents of chlorophyll and active iron, and increased Fe accumulation in cell organelles were observed in SA+SNP treated young leaves, suggesting that an improvement of iron availability in plants. Moreover, the improved nutrient solution pH, increased H+-ATPase activity and increased iron concentration in roots in SA+SNP treated plants, suggesting that SA+SNP is effective in modulating iron uptake. Furthermore, the increased calcium (Ca), magnesium (Mg) and zinc (Zn) concentrations and decreased manganese (Mn) and copper (Cu) concentrations in the leaves and roots of peanut indicated that SA+SNP stimulated the maintenance of ions disturbed by Fe deficiency. In addition, SA+SNP alleviated the increased accumulation of superoxide anion (O2•-) generation rate and malondialdehyde (MDA), and modulated the antioxidant enzymes.ConclusionsThese results indicated that the interaction of SA and SNP promoted Fe uptake, translocation and activation; modulated the balance of mineral elements; and protected Fe deficiency induced oxidative stress. Therefore, SA and SNP had synergistic effects in alleviating chlorosis induced by Fe deficiency.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-9) contains supplementary material, which is available to authorized users.

Hydroponics experiments were conducted to study the effects of sodium nitroprusside (SNP, a donor of NO) on lead toxicity in ryegrass (Lolium perenne L.) seedlings. When the ryegrass seedlings were grown in a nutrient solution containing 500 μM Pb 2+ for two weeks, the plant biomass as well as net photosynthetic rate, transpiration rate, chlorophyll and carotenoid content of leaves decreased. The Pb stress also induced the production of superoxide anion (O 2•− ) and hydrogen peroxide (H 2 O 2 ), leading to malondialdehyde (MDA) accumulation. Furthermore, the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) decreased in the Pb-treated seedlings, but the catalase (CAT) activity increased. Additionally, the content of Cu in shoots and the content of K, Mg, Fe, and Zn in both shoots and roots decreased, but the content of Ca in shoots and roots increased under the Pb stress. Moreover, Pb accumulated mostly in roots, whereas a small quantity was translocated to shoots. However, the addition of 50, 100, and 200 μM SNP into the solution containing Pb increased the chlorophyll content and net photosynthetic rate, reduced Pb-induced oxidative damages, improved antioxidant enzyme activities, and inhibited translocation of Pb from roots to shoots. In particular, 100 μM SNP had the best effect on promoting growth of the ryegrass seedlings under the Pb toxicity. However, the application of 400 μM SNP had no obvious alleviating effect on Pb toxicity in the ryegrass seedlings.

A hydroponics experiment was conducted to test the effects of sodium nitroprusside (SNP, a donor of NO) supplied with different concentrations on copper (Cu) toxicity in ryegrass seedlings (Lolium perenne L.). Excess Cu (200 µM) reduced chlorophyll content, resulting a decrease in photosynthesis. Cu stress induced the production of hydrogen peroxide (H 2 O 2) and superoxide anion (O 2 • −), leading to malondialdehyde (MDA) accumulation. Furthermore, activities of antioxidant enzymes in Cu-treated seedlings such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were decreased. In addition, Cu stress inhibited the uptake of K, Mg, Fe, and Zn and increased Ca content in roots. Moreover, in leaves of Cu-stressed seedlings, K, Fe, and Zn contents were decreased and the contents of Ca and Mg were not affected significantly. In Cu-treated seedlings, Cu concentration in roots was higher than in leaves. Addition of 50, 100, 200 µM SNP in Cu-mediated solutions increased chlorophyll content and photosynthesis, improved antioxidant enzyme activities, reduced Cu-induced oxidative damages, kept intracellular ion equilibrium under Cu stress, increased Cu concentration in roots and inhibited Cu accumulation in leaves. In particular, addition of 100 µM SNP had the best effect on promoting growth of ryegrass seedlings under Cu stress. However, the application of 400 µM SNP had no obvious alleviating effect on Cu toxicity in ryegrass seedlings.

To study the exogenous salicylic acid (SA) to alleviate the cadmium (Cd) toxicity in ryegrass (Lolium perenne L.), ryegrass plants subjected to 100 lM CdCl 2 exposure were treated with different concentrations of SA, and Cd toxicity was evaluated by the decreases in plant growth and chlorophyll content. In Cd-treated plants, the activities of antioxidant enzymes, such as superoxide dismutase, peroxidase and catalase, decreased dramatically in both shoots and roots, whereas the accumulation of superoxide anion (O 2 Á-), hydrogen peroxide (H 2 O 2 ) and malondialdehyde (MDA) increased significantly. Excess Cd also decreased soluble protein and ascorbic acid (AsA) contents, increased accumulation of Cd in both shoots and roots; furthermore, the absorption of micronutrients was inhibited. Addition of 200 lM SA had the most significant alleviating effect against Cd toxicity while the addition of 400 lM SA had no significant effect with Cd treatment. Addition of 100, 200, 300 lM SA considerably increased chlorophyll content and the activities of antioxidant enzymes, increased the uptake and translocation of mineral elements, and decreased H 2 O 2 and MDA accumulation in both shoots and roots of Cd-stressed plants. Addition of 200 lM SA not only decreased the Cd uptake in ryegrass, but also decreased the root-to-shoot translocation of Cd and changed its subcellular distribution in plants. Addition of 200 lM SA increased Cd concentrations in soluble fraction and cell wall in both shoots and roots markedly, with the majority of Cd associated with the cell wall and the soluble fraction and a minor part of Cd present in the cell organelle. Based on these results, we conclude that the optimal concentrations of exogenous SA could alleviate Cdinduced stress and promote ryegrass plant growth.

The interactive effects of salicylic acid (SA) and nitric oxide (NO) on alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L.) were studied. Seedlings of two cultivars (Huayu 22 -a big seed type, and Xiaobaisha -a small seed type) were treated with 200 µM CdCl 2 without or with 0.1 mM SA or 0.25 mM sodium nitroprusside (SNP, an NO donor). Results show that the Cd exposure depressed plant growth of both the cultivars but more of Huayu 22 than of Xiaobaisha. Exogenous SA and NO alleviated Cd toxicity in both the peanut cultivars: they improved growth, chlorophyll content, photosynthesis, and mineral nutrition. Furthermore, exogenous SA or NO decreased oxidative stress by increasing activities of antioxidant enzymes and content of non-antioxidants. Besides, in roots and leaves of both the cultivars, exogenous SA and NO increased Cd accumulation in the cell wall and decreased Cd distribution to organelles. In particular, the effect of SA+SNP was most obvious.