Growth Traits and Electrophysiological Responses of Cardamine violifolia to Selenium Biofortification Under Various Selenomethionine Levels.

Selenomethionine (SeMet) is essential for selenium fortification in the hyper-selenophilous plant, Cardamine violifolia (Cv). However, there is currently a lack of real-time monitoring techniques to investigate SeMetfortification in Cv. In this study, we employed a time-course experiment (0-10 days) under different concentrations of SeMet (0-300 mg/L). Based on the growth characteristics of Cv, SeMet supplementation was most effective on day 4 at 100 mg/L. Compared with CK, the fresh weight of the roots, stems, and leaves, as well as the total chlorophyll and total nitrogen content, increased by only 2.7-32.9%. Furthermore, based on electrophysiological water metabolism and nutrient translocation in Cv leaves, an electrophysiological indicator, ESR, was used to evaluate selenium biofortification with SeMet. We found that electrophysiological responses are more sensitive than growth traits; the intrinsic capacitance (ICp) of S2 is 173% higher than that of CK, whilst IR, IZ, IXC and IXL are reduced from 44.4% to 73.68%. Intracellular water-holding capacity (IWHC), water transfer rate (WTR), nutrient translocation rate (NTR), and electrophysiological metabolic activity (MA) increased by 144-264%, enhancing SeMet enrichment efficiency. However, when SeMet > 100 mg/L (S3-S6), intracellular water metabolism and active nutrient transport were reduced, leading to the IWHC of S6 being 32.8% lower than CK. Moreover, although the ESR of S6 is higher than CK, the total SeMet transport capacity (STC) of Cv is reduced, promoting the efflux of SeMet (ES2) to inhibit high SeMet stress. Correlation analysis indicated that the electrophysiological selenium-enhancing rate (ESR) is significantly positively correlated with Cv biomass (R2 = 0.89, p ≤ 0.05) and leaf area (R2 = 0.85, p ≤ 0.05), showing that it served as an electrophysiological factor of selenium biofortification. Hence, plant electrophysiological technology enables real-time monitoring of different SeMet biofortification in Cv, and ESR can provide a useful reference for assessing selenium biofortification in hyperaccumulators.