Anthocyanin production in the hyperaccumulator plant Noccaea caerulescens in response to herbivory and zinc stress

In the current study, potential involvement of anthocyanins in the defence of the Zn hyperaccumulator plant, Noccaea caerulescens, was investigated in two independent glasshouse experiments. Plants were grown in compost amended with a range of Zn concentrations. In the first experiment, foliar herbivory was simulated by clipping the shoots with scissors, whilst in second experiment, plants were subjected to natural herbivory by thrips (Frankliniella occidentalis). In both experiments, foliar Zn concentrations were approximately twice as high as that applied to the soil, indicating accumulation occurred. In the clipping experiment, foliar anthocyanin concentrations decreased by 22-45 % with increasing soil Zn amendments and clipping increased anthocyanin concentrations by 17-24 % relative to unclipped plants. In a thrips feeding experiment, Zn treatment had little effect on anthocyanin content although there was a trend towards increased anthocyanin production in plants grown at the lower concentrations of Zn. Anthocyanin concentration increased by 49-52 % in N. caerulescens leaves subjected to thrip attack compared to that of thrip-free shoots. Thus, anthocyanins increased as a result of foliar damage (manual clipping and natural herbivory) and generally decreased with enhanced Zn concentrations. Foliar glucosinolate concentrations were higher in ungrazed leaves than in grazed leaves of the same thrip-infested plants, whilst anthocyanin production was higher in the grazed leaves. The possibility of an interaction between glucosinolate and anthocyanin production resulting from herbivory is discussed.