New evidence of the timing of arsenic accumulation and expression of arsenic-response genes in field-grown Pteris vittata plants under different arsenic concentrations

The timing and efficiency of arsenic (As) accumulation is crucial for using the hyperaccumulator P. vittata in remediation of As-contaminated soils. In this study, through an innovative microXRF-based approach, using a new "pinna powder" sampling method, we monitored As accumulation over time in fronds of individual P. vittata plants grown in the greenhouse and in the field on two natural soils, with high (750 mg/kg) and moderate (58.4 mg/kg) As concentrations. Results, validated by multivariant statistical analysis show that the peak of As occurs on both soils at 45/60 days and at 100/120 days in greenhouse and field grown plants, respectively. Furthermore, in field trials, the timing of As accumulation in both soils was similar during the first autumn-winter and the second spring-summer phytoextraction cycle. After the two cycles, soil As content was reduced by 70.4% in the high-As soil and 26.4% in the moderate one. Moreover, candidate genes involved in As hyperaccumulation-the arsenite antiporter PvACR3, , the As (V)-reductases Pv2.5-8 and the organic cation transporter PvOCT4-- are expressed in response to As in field-grown plants with similar kinetics in both soils. In conclusion, we established by this innovative technique, the timing of maximum As accumulation that is linked to the intrinsic hyperaccumulation mechanism and represents a highly powerful tool to set up the duration of phytoextraction cycles.