The use of plants to remove heavy metals from soil (phytoremediation) is expanding due to its cost-effectiveness as compared to conventional methods and it has revealed a great potential. Since contaminants such as Pb or Cd have a limited bioavailability in the soil, methods to facilitate their transport to the shoots and roots of plants are required for successful phytoremediation. The objective of this study was to investigate the effects of addition of different rates (0, 3, 6 and 12 mmol/kg) of ethylene diaminetetraacetate (EDTA) on heavy metal availability in soils contaminated with 50 mg/kg Cd (CdCl 2 ), 50 mg/kg Cu (CuSO 4 ), 50 mg/kg Pb [Pb(NO 3 ) 2 ] and 50 mg/kg Zn (ZnSO 4 ), and on the capacity of canola (Brassica napus L.) and Indian mustard (Brassica juncea L.) plants to uptake Cu, Cd, Pb and Zn in a growth chamber. Results indicated that EDTA application increased heavy metal availability and uptake by plants. Significant differences were obtained in both species and plant parts. As for plant species tested, canola was more effective in the uptake of Cu, Cd, Pb and Zn. Root heavy metal uptake of both species was higher than shoot heavy metal uptake.

No abstract

Nowadays, due to the environmental stress factors that limit the production of crops, it has become very difficult to find suitable areas to enable the plant to reach its optimum product potential. Abiotic stress is very effective in decreasing agricultural production. Factors such as drought, salinity, high and low temperature, flood, radiation, heavy metals, oxidative stress, and nutrient deficiency can be considered as abiotic stress factors, and these sources of stress negatively affect plant growth, quality and productivity. Melatonin (MEL) was first identified in plants in 1995 and is increasingly becoming important for its role and effects in the plant system. MEL has been shown to have a substantial role in plant response to growth, reproduction, development, and different stress factors. In addition to its regulatory role, MEL also plays a protective role against different abiotic stresses such as metal toxicity, temperature, drought, and salinity. In plants, an important role of MEL is to alleviate the effects of abiotic stresses. In this review, the effects of MEL on plant growth, photosynthetic activity, metabolism, physiology, and biochemistry under abiotic stress conditions as a plant growth regulator will be examined.

Ultraviolet-B (UV-B) radiation is one of the most important abiotic stress factors that could influence plant growth, development, and productivity. Nitric oxide (NO) is an important plant growth regulator involved in a wide variety of physiological processes. In the present study, the possibility of enhancing UV-B stress tolerance of lettuce seedlings by the exogenous application of sodium nitroprusside (SNP) was investigated. UV-B radiation increased the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD) and total phenolic concentrations, antioxidant capacity, and expression of phenylalanine ammonia lyase (PAL) gene in seedlings, but the combination of SNP pretreatment and UV-B enhanced antioxidant enzyme activities, total phenolic concentrations, antioxidant capacity, and PAL gene expression even more. Moreover, UV-B radiation significantly inhibited chlorophylls, carotenoid, gibberellic acid (GA), and indole-3-acetic acid (IAA) contents and increased the contents of abscisic acid (ABA), salicylic acid (SA), malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide radical (O2•(-)) in lettuce seedlings. When SNP pretreatment was combined with the UV-B radiation, we observed alleviated chlorophylls, carotenoid, GA, and IAA inhibition and decreased content of ABA, SA, MDA, H2O2, and O2•(-) in comparison to non-pretreated stressed seedlings.

IntroductionVegetable crops grown under organic conditions play an important role in the global economy. Hence, some organic substances, such as humic acid (HA) and its salts calcium humate and boron humate, are used for plant cultivation around the world. Humic substances constituting 65%-70% organic matter are used in various areas of agriculture, namely plant physiology and environmental science, because of the multiple roles they play in these areas (Russo and Berlyn, 1990;Türkmen et al., 2004). HAcontaining elements improve soil fertility and increase the availability of nutrient elements by holding them as mineral surfaces (El-Sharkawy and Abdel-Razzak, 2010;Paksoy et al., 2010). The important functional groups of HA include alcoholic hydroxyl, carboxyl, ketone, phenolic hydroxyl, and quinone (Russo and Berlyn, 1990). The mechanism of HA that promotes plant growth is not exactly known, but several explanations have been provided by researchers for increased oxygen uptake, respiration, photosynthesis, cell membrane permeability, phosphate uptake, and root cell elongation (Russo and Berlyn, 1990). Böhme and Lua (1997) stated that HA has important effects on nutrient uptake by plants and is also particularly important for the transport and availability of micronutrients.Studies of the positive effects of HA on plant development have indicated the significance of optimum

Lucerne (Medicago sativa L.) is grown as a forage crop on many livestock farms. In calcareous soils in eastern Turkey, lucerne production requires boron (B) addition as the soils are naturally B deficient. Field experiments with four Bapplication rates (0, 1, 3, and 9 kg ha (1 B) were conducted in 2005 and 2006 to determine the optimum economic B rate (OEBR), critical soil test and tissue B values for dry matter (DM) production for lucerne grown on B-deficient calcareous aridisols in eastern Turkey. Boron application increased yield at each site in both years of production. The OEBR and critical soil and tissue B content were not impacted by location. Averaged over the two years and three locations, the OEBR was 6.8 kg B ha (1 with an average DM yield of 12.0 Mg ha (1 . The average soil B content at the OEBR was 0.89 mg kg (1 while leaf and shoot tissue B content amounted to 51.8 and 35.5 mg kg (1 , respectively. Boron application decreased tissue calcium (Ca), zinc (Zn), and copper (Cu), and increased tissue nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), iron (Fe), and manganese (Mn). Tissue and soil B increased without impacting yield at B levels up to 9 kg ha (1 . We conclude that 7 kg ha (1 B is sufficient to elevate soil test B levels from 0.11 to 0.89 mg kg (1 and overcome B deficiency at each of the sites in the study. Similar studies with different soils and initial soil test B levels are needed to conclude if these critical soil and tissue values can be applied across the region.

Boron (B) is an essential micronutrient required for normal plant growth and development. Boron management is challenging because the optimum B application range is narrow and the application rates vary from one soil to another. Boron deficiency is widespread in the Anatolia region of Turkey. This may impact on yield and mineral contents of leaves and fruits of strawberry (Fragaria×ananassa cv. Fern) especially in B-deficient calcareous Aridisols in Eastern Anatolia, Turkey. A 2-year field experiment was conducted to study yield and quality response of strawberry to B application. Boron fertilizer application affected plant yield and chemical composition. B application decreased tissue nitrogen (N) and calcium (Ca) but increased tissue phosphorus (P), potassium (K), manganese (Mn), zinc (Zn) and copper (Cu) content. We conclude that a B addition of 5.5 kg ha−1 is sufficient to elevate soil B levels to non-deficient levels

No abstract