Application of measuring electrochemical characteristics on plant root surfaces in screening Al-tolerant wheat

To explore the relationship between Al phytotoxicity and the electrochemical characteristics of wheat root surfaces, a new chemical mechanism for tolerance of wheat to Al toxicity was initially proposed by conducting acute root elongation experiment, adsorption/desorption experiment, streaming potential determination, and infrared spectroscopy (ATR-FTIR) analysis respectively to classify the grade of Al tolerance of 92 wheat cultivars and quantitatively characterize the electrochemical properties of their root surfaces. Then a pot experiment was conducted with the screened wheat cultivars with different Al resistance grown on acid soils to verify their tolerance to Al toxicity. Results show that zeta potentials of the roots of 67 wheat cultivars at pH4.46 were significantly negatively correlated with Al(Ⅲ) adsorbed on the roots and their relative root elongation (P < 0.05), indicating that wheat roots with less negative charges is more tolerant to Al toxicity. Based on the mechanism, 14 Al-tolerant, 23 medium Al-tolerant and 30 Al-sensitive wheat cultivars were classified. The pot experiment reveals that the relative dry weight of Al-tolerant wheat cultivars was generally greater than that of medium Al-tolerant and Al-sensitive wheat cultivars and Al-tolerant wheat cultivars accumulate less Al in their shoots, which further verifies the relationship among charge characteristics, tolerance of wheat to Al toxicity, and Al uptake by wheat. The negative charges derived from organic functional groups on root surfaces could influence the exchangeable and complexed Al(Ⅲ) adsorbed on wheat roots and thereby affect Al tolerance of wheat cultivars. This finding not only provides a new perspective to screen Al-tolerant wheat cultivars and explain the mechanism of tolerance of wheat to Al toxicity, but is also useful for the prediction of differences in the uptake of Al in the shoots between Al-tolerant and Al-sensitive wheat cultivars, and finally contributes to the prevention of food security risk caused by Al in acid soils.