Effects of foliar application of salicylic acid and nitric oxide in alleviating iron deficiency induced chlorosis of Arachis hypogaea L

Abstract

Background: The 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).

Results: The 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.

Conclusions: These 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.

Keywords: Active iron; Antioxidant enzymes; Arachis hypogaea L.; Mineral elements; SA; SNP.

Figure 1

Effects of exogenous SA and NO on the activities of plasma membrane H⁺-ATPase (A) and Ca²⁺-ATPase (B) in roots of peanut seedlings and changes of pH in culture medium (C and D). Different lower case letters in the same line indicate a significant difference (P < 0.05) between different treatments. The values are means ± SD of three replicate samples per treatment. CK: hydroponic systems; EDTA-Fe: Hoagland nutrient solution containing 0.1 mM EDTA-Fe; SA: hydroponic systems and foliar application of 1.0 mM SA; SNP: hydroponic systems and foliar application of 2.5 mM SNP; SA+SNP: hydroponic systems and foliar application of 1.0 mM SA and 2.5 mM SNP; 1/2(SA+SNP): hydroponic systems and foliar application of 0.5 mM SA and 1.25 mM SNP.

Figure 2

Effects of different treatments on tissue distribution of Fe in peanut roots (A) or leaves (B). Different lower case letters in the same line indicate a significant difference (P < 0.05) between different treatments. The values are means ± SD of three replicate samples per treatment. CK: hydroponic systems; EDTA-Fe: Hoagland nutrient solution containing 0.1 mM EDTA-Fe; SA: hydroponic systems and foliar application of 1.0 mM SA; SNP: hydroponic systems and foliar application of 2.5 mM SNP; SA+SNP: hydroponic systems and foliar application of 1.0 mM SA and 2.5 mM SNP; 1/2(SA+SNP): hydroponic systems and foliar application of 0.5 mM SA and 1.25 mM SNP.

Figure 3

Effects of exogenous SA and NO on the concentrations of K (A), Mg (B), Ca (C), Cu (D), Zn (E), and Mn (F) of peanut. Different lower case letters in the same line indicate a significant difference (P < 0.05) between different treatments. The values are means ± SD of three replicate samples per treatment. CK: hydroponic systems; EDTA-Fe: Hoagland nutrient solution containing 0.1 mM EDTA-Fe; SA: hydroponic systems and foliar application of 1.0 mM SA; SNP: hydroponic systems and foliar application of 2.5 mM SNP; SA+SNP: hydroponic systems and foliar application of 1.0 mM SA and 2.5 mM SNP; 1/2(SA+SNP): hydroponic systems and foliar application of 0.5 mM SA and 1.25 mM SNP.