Enhancement of Fe tolerance in Polygonum thunbergii naturally growing in mine pond at the reproduction stage

Polygonum thunbergii Sieb. et Zucc., an annual herb, has been known to grow naturally at mine sites. This study examined the Fe tolerance mechanisms in P. thunbergii growing in a mine pond, considering carbon allocation to potential Fe-tolerance factors. Fe concentrations in P. thunbergii collected from June to October 2021, were high especially in live and dead adventitious roots. In the live adventitious roots, Fe detoxicants (phenolic compounds; gallic acid, procyanidin B2, procyanidin A2, and condensed tannins) and Fe localization in the epidermal cell walls could influence Fe tolerance. Fe accumulation in the dead adventitious roots could be related to Fe tolerance because metal accumulation in dead plant tissues is important to decrease Fe toxicity as exclusion site. In addition, the proportion of carbon used for phenolic compounds significantly increased in live adventitious roots at the flowering time in September. Significantly less carbon for Fe exclusion by dead adventitious roots was also detected at the flowering time. Our results suggest that in order to establish the next generation , P. thunbergii could enhance Fe tolerance at the reproduction stage. • Polygonum thunbergii in mine pond accumulated high Fe in live and dead roots. • Live roots produced phenolics to detoxify Fe and dead roots work to exclude Fe. • Carbon allocation to phenolics in live roots increased at the flowering time. • Less carbon for Fe exclusion in dead roots was detected at the flowering time. • At the reproduction stage, P. thunbergii would enhance Fe tolerance in mine pond.