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Manganese (Mn) is an essential nutrient in most organisms. Establishing an effective regulatory system of Mn absorption is important for sustainable crop development. In this study, we selected sunflower as the model plant to explore the effects of 5-aminolevulinic acid (ALA) or salicylic acid (SA) combined with citric acid (CA) on Mn absorption. Six-leaf-old sunflower plants were exposed to 0.8 g kg−1 Mn for one week and then treated with chelating agents, i.e., CA (10 mmol kg−1), and different concentrations of ALA and SA for one week. The results showed that Mn-treated plants had significantly increased H2O2, O2− and MDA contents in leaves compared with the control. Under the Mn + CA treatment, ALA or SA2 significantly activated the antioxidant defense system by increasing SOD, POD and CAT activities in leaves. Moreover, the application of CA significantly increased the Mn uptake in sunflower roots compared with Mn treatment alone; however, did not accelerate the translocation efficiency of Mn from sunflower roots to shoots. Moreover, ultrastructural and RT-qPCR results further demonstrated that ALA/SA could recover the adverse impact of excessive Mn accumulation in sunflowers. Like a pump, ALA/SA regulated the translocation efficiency and promoted the transportation of Mn from roots to shoots. This study provides insights into the promotive role of ALA/SA combined with CA on sunflower growth by regulating Mn absorption, which would be beneficial for regulating Mn absorption in soil with an Mn deficit. [ABSTRACT FROM AUTHOR]

Foliar sprays with micronutrients are widely employed in agricultural production as an alternative to improve soil fertilization and plant nutritional status. We hypothesized that less water-soluble sources of manganese (Mn; MnCO3) could serve as a slow-release source compared to a water-soluble source (MnSO4.H2O). Our goal here was to evaluate Mn-sources (MnSO4.H2O and MnCO3) and rates (150; 250; 350; and 450 g ha−1) sprayed in the 3rd and 4th trifoliate leaflets of soybean growing in clayey and sandy soil under controled conditions. In phenological stages V7 (vegetative period) and R1 (reproductive period), dry matter, height, the diameter of the stem, and Mn-content in the shoot, stem, and in the trifoliate leaflets were determined. Results showed that the application of Mn resulted in an augmented Mn-content in the 3rd and 4th trifoliate leaflets (sandy) and the 3rd and 5th trifoliate (clayey). The MnSO4.H2O promoted Mn-retranslocation from the 3rd/4th trifoliate to the stem and the 5th/6th trifoliate. However, MnCO3 was accumulated in the 3rd/4th trifoliate. The Mn-rates presented a linear response in sandy soil and quadratic response in clayey soil. Clayey soil was characterized by the higher Mn-contents in the stem, while sandy soil presented the higher Mn-contents in the 3rd, 4th, 5th, and 6th trifoliate. Our results suggest that MnSO4.H2O is more effective in increasing Mn-content in soybean leaves during plant development due to the Mn-retranslocation to sink organs (5th/6th trifoliate leaflets and shoot). [ABSTRACT FROM AUTHOR]

Manganese (Mn) is an essential nutrient in most organisms. Establishing an effective regulatory system of Mn absorption is important for sustainable crop development. In this study, we selected sunflower as the model plant to explore the effects of 5-aminolevulinic acid (ALA) or salicylic acid (SA) combined with citric acid (CA) on Mn absorption. Six-leaf-old sunflower plants were exposed to 0.8 g kg−1 Mn for one week and then treated with chelating agents, i.e., CA (10 mmol kg−1), and different concentrations of ALA and SA for one week. The results showed that Mn-treated plants had significantly increased H2O2, O2− and MDA contents in leaves compared with the control. Under the Mn + CA treatment, ALA or SA2 significantly activated the antioxidant defense system by increasing SOD, POD and CAT activities in leaves. Moreover, the application of CA significantly increased the Mn uptake in sunflower roots compared with Mn treatment alone; however, did not accelerate the translocation efficiency of Mn from sunflower roots to shoots. Moreover, ultrastructural and RT-qPCR results further demonstrated that ALA/SA could recover the adverse impact of excessive Mn accumulation in sunflowers. Like a pump, ALA/SA regulated the translocation efficiency and promoted the transportation of Mn from roots to shoots. This study provides insights into the promotive role of ALA/SA combined with CA on sunflower growth by regulating Mn absorption, which would be beneficial for regulating Mn absorption in soil with an Mn deficit.

A new type of multi-color PAM chlorophyll fluorometer (Schreiber et al. ) was applied for measurements of photodamage to photosystem II (PS II) in optically thin suspensions of Chlorella (200 μg Chl l) in the presence of 1 mM lincomycin. An action spectrum of the relative decrease of F/ F in the 440-625 nm range was measured, which not only showed the expected high activity in the blue, but at a lower level also substantial activity above 540 nm. With the same dilute suspension, a PS II absorption spectrum was derived via measurements of the O-I rise kinetics induced by differently colored strong light at defined incident quantum flux densities. After normalization of the two spectra at 625 nm, the relative extent of photodamage at 440-480 nm proved substantially higher than absorption by PS II, whereas the two spectra were close to identical in the 540-625 nm range. Hence, overall photodamage to PS II appears to consist of two components, one of which is due to light absorbed by PS II pigments, whereas the other one is likely to involve direct light absorption by Mn in the oxygen-evolving complex (Hakala et al. Biochim Biophys Acta 1706:68-80, ). Based on this rationale, an action spectrum of the Mn mechanism of photodamage was deconvoluted from the overall action spectrum, declining steeply above 480 nm. An almost identical Mn-spectrum was derived by another approach with the PAR of the various colors being adjusted to give identical rates of PS II turnover, PAR. The tentative, basic assumption of negligibly small contribution of the Mn mechanism to photodamage above 540 nm was supported by supplementary measurements using an external 665 nm lamp. 665 nm not only gave about two times PS II turnover as compared to 625 nm, but also about two times photodamage. [ABSTRACT FROM AUTHOR]