Chelates are compounds that are applied to improve nutrition, especially the micronutrients status of plant tissues. During past decades, various chelating agents have been synthesized and introduced to agricultural systems. The recent formulas are aminochelates that are synthesized using various amino acids and a single or several nutrient ions aimed at improving fertilizer use efficiency and more adaptation to environment protection. Apart from their primary use as a micronutrient source, aminochelates represent an effective nitrogen (N) fertilizer in plant nutrition that can avoid negative effects from simple N fertilizers, such as urea. In various studies, higher yield and quality as well as higher concentration of nutrient elements have been obtained by application of aminochelates rather than simple chemical fertilizers. These compounds claimed to be more natural and safer forms of chelating agents, with higher use efficiency and without environmental side effects. However, there is lack of sufficient knowledge especially regarding their detailed impacts and their fate within the soil and plant system. This review provides information concerning the role of aminochelates in plant nutrition and to summarize the previous recent studies that have been done using these fertilizers.

Background: Soil salinity is a real challenge in nowadays crop production in many regions. Various strategies have been applied to increase plant salinity tolerance. Salicylic acid (SA) frequently has been reported to increase plant salinity tolerance; however, the comparative efficiency of soil (root) or foliar application of SA has not been well tested yet. In this study, the effects of root or leaf pretreatment, and leaf treatment with 100 mg L⁻¹salicylic acid were evaluated on growth characteristics of tomato seedlings (Solanum lycopersicumMill) under salinity stress. The plants were grown 3 weeks in sand that were fed with Hoagland nutrient solution with or without 100 mM NaCl.Results: The results showed that salinity significantly reduced tomato seedling growth and traits of plant height, leaf area, shoot fresh weight, and nutrient concentration of potassium, calcium, iron and zinc compared to control plants. However, leaf SPAD value, root fresh and dry weights, leaf concentration of sodium, proline and soluble sugars were significantly increased under 100 mM NaCl salinity compared to control plants. Application of salicylic acid particularly by foliar pretreatment increased the tomato plant growth and those traits that were reduced by NaCl salinity. Application of SA, particularly foliar pretreatment, also increased the root fresh and dry weights, leaf proline and soluble sugars concentrations as compared with salinity alone. Foliar SA pretreatment significantly increased leaf K and Fe concentrations, whereas leaf Ca was significantly increased by either root or leaf pretreatment with SA under salinity.Conclusion: The results indicate that the most to least effective method of SA application was leaf pretreatment, root pretreatment and leaf treatment, respectively, to recover the reduced growth parameters of tomato plant under salinity stress.

Amino acids have various roles in plant metabolism, and exogenous application of amino acids may have benefits and stimulation effects on plant growth and quality. In this study, the growth and nutrient uptake of Romain lettuce (Lactuca sativa subvar Sahara) were evaluated under spray of glycine or glutamine at different concentrations of 0 (as control), 250, 500 and 1000 mg.L^-1, as well as a treatment of 250 mg.L^-1 glycine+250 mg.L^-1 glutamine. The results showed that there was significant increase in leaf total chlorophyll content under Gly250+Glu250, Gly250 and Glu1000 mg.L^-1treatments, and in leaf carotenoids content under 250 mg.L^-1 glutamine spray compared with the control plants. Shoot fresh and dry weights were highest under 500 mg.L^-1 glycine, whereas root fresh weight was highest under 250 mg.L^-1 glycine spray. Foliar application of glycine and glutamine had no significant increase in leaf mineral concentrations except for iron, in which 1000 mg.L^-1Gly spray resulted in significantly higher leaf Fe concentration compared with the control plants. Leaf vitamin C was increased at 250 and particularly 500 mg.L^-1 spray of glycine and glutamine compared with the control. Nevertheless, different amino acid treatments had no significant effect on plant height, leaf SPAD value, root dry weight, and leaf concentrations of N, K, Ca, Mg and Zn. The results indicate that foliar application of glycine and glutamine amino acids can have beneficial effects on lettuce growth, as higher fresh yield, leaf chlorophyll content and vitamin C were obtained by low to moderate concentrations of glycine and/or glutamine amino acids.

Background: Contamination of vegetable crops with heavy metals is a great threat to human health. On the other hand, monitoring plant tissue content of heavy metals at different growth stages could have important implications. In this study, shoot and root samples of garden cress and sweet basil were collected from five farms, from heavy metal polluted fields located in Shahre Rey, south of Tehran, Iran, in either young (3 weeks old) or mature (7 weeks old) plants. The concentrations of cadmium (Cd), lead (Pb), nickel (Ni), arsenic (As), chromium (Cr), cobalt (Co), copper (Cu), manganese (Mn) and zinc (Zn) in plant tissues were determined using atomic absorption spectroscopy. In another study, 2 weeks (young) or 6 weeks old (mature) plants of garden cress were subjected to three concentrations of Cd and Pb (0, 5, 10 mg L⁻¹) under hydroponic sand culture for 5 days, in which Hoagland formula was used for nutrient solution preparation. Results: The results showed that root concentration of various heavy metals, particularly Cd, As, Ni, Co, Cu, Mn and Zn but not Pb were significantly higher than their shoot concentration in either crop under field sampling. The leaf concentration of some heavy metals was significantly different in seedling and older (mature) plant samples of either crop. Young plant leaves of sweet basil had significantly less Cd, Pb, As and higher Cu than mature plants, whereas young garden cress plants had similar Cd, Pb and higher As and Zn concentrations than mature plants. The Cr, Co, Mn and Zn concentrations were similar in young and mature plants of sweet basil. The Mn, Co, Cr and Ni concentration of young and mature plants of either crop was also similar. The result of hydroponic study showed that young plants of garden cress had higher potential to accumulate lead in shoot and root, particularly in lower (5 mg L⁻¹) than higher (10 mg L⁻¹) lead concentration; however, root Pb concentration at 10 mg L⁻¹ Pb of nutrient solution showed no difference between young and mature plants. Regarding cadmium, young garden cress plants accumulated higher Cd than mature plants in their shoot, particularly under higher Cd levels (10 rather than 5 mg L⁻¹) of nutrient solution; however, a wide difference in root Cd concentration was observed under low (5 mg L⁻¹) than higher (10 mg L⁻¹) cadmium concentration of nutrient solution. Conclusion: The results of these two studies indicate that despite that young plants have a higher potential for heavy metal uptake and accumulation, the low difference in young and mature plants in the polluted fields may be due to the longer period of plant growth of mature plants that may increase the risk of exposure to polluted air and dust deposition containing high levels of heavy metals.

Background: Soil salinity buildup and soil degradation are emerging challenges in cropping systems practicing high chemical fertilization. Application of biostimulants and organic fertilizers are better deserve agricultural sustainability and are generally reflected in more nutritious foods than chemical fertilization. Materials and methods: In this study, the growth, quality and antioxidant capacity of coriander (Coriandrum sativum L.) were evaluated under application of organic and biological compared to chemical fertilization in a pot experiment. Different soil fertilization treatments including vermicompost (20% pot volume), cow manure (20% pot volume), biophosphate (as seed inoculation), glycine amino acid (as a biostimulant at 300 mg/kg soil), mixed NPK fertilizer (at 600 mg/kg soil) and unfertilized control were applied to plants under a completely randomized design with four replications. Results: The results showed that application of organic fertilizers mainly vermicompost and glycine, and to lesser extent NPK fertilizer significantly increased many growth, yield and biochemical quality traits of coriander including root and shoot biomass, leaf SPAD value, ascorbic acid, mineral nutrients, flavonoids and antioxidant activity compared to control plants. Fertilization practices resulted in higher biomass production of root (all treatments) and shoot (all treatments except biophosphate) than control plants. Leaf minerals including N and K (in vermicompost, NPK and glycine treatments), leaf P and Fe (in vermicompost and glycine treatments), leaf Zn (in vermicompost treatment) were significantly increased compared to control plants. Application of manure recorded the lowest leaf Ca and total phenols, while the highest leaf Ca was in vermicompost and glycine-treated plants and the highest leaf phenols was in vermicompost treatment. Application of glycine resulted in the highest leaf ascorbic acid as well as catalase enzyme activity. Leaf antioxidant capacity was significantly higher in vermicompost, glycine and NPK treatments compared to control plants. Leaf carotenoids, peroxidase activity, the concentration of Mg, Cu and Mn were not significantly affected by treatments. Conclusion: The results indicate that cow manure and biophosphate treatments were not much effective on plant growth; however, vermicompost and glycine showed promising improvement of coriander growth and antioxidant capacity even more than NPK fertilization. Graphic

Background: Different approaches have been used to improve mineral nutrient status of plants in absence of chemical fertilization and toward safer products and improved human health. Amino acids have been proposed with such roles in different recent studies. In this study, glycine was applied as foliar (250, 500 and 1000 ppm) or as soil (250 and 500 mg/plant) to cucumber plants compared to unfertilized control and NPK fertilization, under greenhouse conditions. Results: The results showed that all glycine treatments increased leaf area and the economic life of plants compared to control. Soil application of glycine at higher concentration of 500 mg/plant was able to produce the same or better records than NPK fertilization, particularly regarding leaf mineral concentration, plant economic life and total yield. Leaf macro- micro-nutrients were most increased under 500 mg soil-glycine application. Foliar spray of 500 ppm glycine resulted in better records than the other two levels, as spray of 1000 ppm glycine showed adverse and toxic effects including leaf necrosis. Fruit firmness was increased only by NPK and soil application of 500 mg glycine, whereas fruit vitamin C was increased by NPK fertilization, soil application of glycine at both levels (250, 500 mg) and foliar application of glycine at 500 ppm compared to control plants. Conclusion: The results indicate that soil application of 500 mg glycine/plant was able to improve leaf mineral and physiological characteristics towards higher yield and quality.