Characteristics of mitochondrial membrane functions and antioxidant enzyme activities in strawberry roots under exogenous phenolic acid stress

The aim of this study is to explore the mechanisms by which exogenous phenolic acids affect mitochondrial membrane function and the activities of the protective enzyme system in strawberry (Fragaria x ananassa Duch. Hokowase.) roots under the effects of phenolic acids accumulated in the rhizosphere of long-term continuous cropping soil. In this study, the rhizosphere soils of five continuous cropping strawberry plots in Dandong city were used as materials. Using the high-performance liquid chromatographic (HPLC) technique, the types and contents of the actual main phenolic acids in strawberry rhizosphere soils were determined. After choosing syringic acid (SA) and phthalic acid (PA) as treatments, Fragaria x ananassa Duch. Hokowase seedlings were treated with 27.0 mu g.g(-1) of SA or PA to investigate the characteristics of root activities, mitochondrial function and protective enzyme activities in the strawberry roots. Separation of the strawberry rhizosphere identified four main phenolic acids [PA, 4-hydroxy benzoic acid (HA), SA and vanillic acid (VA)]. Longer continuous cropping resulted in more phenolic acid contents, but interannual changes in the phenolic acid species were not obvious. Treatment with exogenous SA and PA simultaneously increased the degree of opening of the mitochondrial membrane permeability transition pore (MPTP) of the strawberry roots and decreased the mitochondrial membrane potential (Delta psi m) and Cytochrome Cyt c/a ratio; additionally, the strawberry root activity and H+-ATPase activity were decreased, and even material transport and energy conversion of the strawberry roots were affected. The hydrogen peroxide (H2O2), superoxide anion radical (O-2-) and malondialdehyde (MDA) contents showed a trend of continuous growth, whereas the guaiacol peroxidase (POD) and SOD activities decreased continuously. The effect of SA was stronger than that of PA.