| Arsenic (As) is known to be one of the most dangerous toxic farmland pollutants. Besides various adverse effects of As on humans and animals, arsenic could also hamper normal growth of plants. Leafy vegetable is a food crop with higher protein and is also an important source of minerals which is essential for good health. Due to the large consumption, the safety measures of leafy vegetables is of great importance for ensuring lower concentration of As in the food. In order to improve agricultural products’safety and to reduce arsenic threat on human health, it is therefore essential to understand the variations of different cultivars in As uptake and its translocation and to evaluate the mechanisms involved in asenic uptake kinetic of cultivars. This helps to screen and find out excluder-cultivars which transport less As concentration to the shoot suitable for growing in the As-contaminated farmlands. In this study, hydroponics culture was employed to screen thirty two different cultivars of leafy vegetable from five species namely romaine (Lactuce sativa var.longifolia), lettuce (Lactuce sativa), Celery (Apium graveolens L.), Amaranth (Amaranthus mangostanus L.) and water spinach (Ipomea aquatica) for As concentration, accumulation, tolerance index, translocation and uptake with different arsenic levels. The main results were showed as follows:1. The impact of arsenic stress treatments on growth parameters through hydroponic experiment was investigated in order to determine the suitable As level by comparing the shoot biomass (Fresh weight) of different leafy vegetable species to those in the control. All of the5species plants could survive well in all As treatments (1,2,4,6,8and10mg L-1As), although their growths were inhibited by high concentrations of As. Shoot biomass, total matter production, root length and shoot height all displayed decreasing trend with increasing concentrations of As, but most of them remained less than the limits of significance. The results showed that variation in tolerance genotypes existed among different species. Romaine and Lettuce were selected as the As-tolerant species, while Celery and Water spinach were selected as the moderate As-tolerant species, finally the As-sensitive species was Amaranth, with the characterization of the significant inhibit of shoot biomass under As stress. Considering the effects of arsenic on shoot biomass alone among3species, the results suggested that among7levels of arsenic that at least6mg L-1As dose could be a suitable level. The results obtained can be useful in the next study with similar As level for developing the selection of cultivars of vegetable with low absorption as a tool for the improvement of food security.2. Genotypic variations in arsenic concentration, accumulation and their translocation within thirty two different cultivars were tested under hydroponics for2weeks, having moderate level of As (6mg L-1). Significant genotypic variations were observed in the shoots As concentration, translocation and bioaccumulation factors revealing more than8,25and8times cultivar differences in shoot As concentration, translocation and bioaccumulation factors respectively. Cultivar Sijibaiye (SJBY) had the lowest shoot As concentration (14.065mg kg-1dry weight) while the highest was detected in Dayekongxincai|DYKXC (112.160mg kg-1dry weight)]. Shoot As concentration in SJBY was about13%of that in cultivar DYKXC. The average As concentration in roots were found to be ten to twenty times higher than those observed in shoots. Arsenic concentrations in shoot of5species were found to follow the trend:Lettuce<Romainc<Amaranth<Celcry<Spinach. The tolerance index (TI), in terms of the biomass ratio of As treatment to control, was high in all cultivars except Dayeqin (DYQ), Baiyexiancai (BYXC) and Yuanyebaixiancai (YYBXC). By contrast,69%of tested cultivars showed a tolerance index higher than90%. Therefore, it has been suggested that there is possibility to lower the As concentration in leafy vegetables by selecting and breeding cultivars with less As concentration that can be safely grown in contaminated soils with the slight and moderate levels of As for safe consumption.3. Uptake ability based on kinetic parameters by two cultivars Texuanyinlingsun (TXYLS) and Sijibaiye (SJBY) were compared in nutrient solution containing different levels of As. Depletion of As from solution was monitored over a period of24h at regular time to estimate As uptake kinetics. Km and Vmax values were evaluated with the aid of the Lineweaver-Burk plot (i.e. the double reciprocal plot of initial velocity (1/v) versus substrate concentration (1/[s]). Whereas both cultivars were capable of assimilating As. The Km and Vmax values for As uptake rate were much lower in SJBY (26.72mg L-1and0.7781.922mg As g-1shoot d.wt.hr"1, respectively) than that of TXYLS (Km81.92mg L"1and Vmax1.84mg As g-1shoot d.wt.hr-1). The time (24h) affects the depletion of As in both cultivars. Based on the results described above, it can be confirmed once again that cultivar SJBY had significantly less uptake of As. Therefore, SJBY might be a promising suitable cultivar to be grown in polluted areas. |
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