Proteomic investigation of Zn-challenged rice roots reveals adverse effects and root physiological adaptation

Aims Understanding the molecular responses of plant roots to the challenging environment contributes to engineering plants with improved stress tolerance. However, little has been done to understand rice (Oryza sativa L.) roots response to the toxic concentration of zinc (Zn) at the proteomic level. This study explored proteomic responses of young rice roots 5-6 days after sowing to 765 mu M of Zn in a hydroponic set-up after 4-day exposure. Methods Dye staining method and spectrophotometry were chosen for physiological response investigations. ICP-MS was used to determine metal content in rice seedlings. Two-dimensional gel electrophoresis was used for the proteomic study of root tissue. Results Elevated Zn reduced Mg translocation to the shoots and Mn uptake, decreased plant growth, and increased cell death of roots. Zn stimulated the biosynthesis of glutathione but decreased ROS and malondialdehyde levels. In total, 42 Zn-responsive proteins were identified. Proteins involved in redox regulation, defense response, sulfur metabolism, and proteolysis were induced, while those of energy production and cell wall biogenesis were decreased. Conclusion Roots of O. sativa seedlings could tolerate certain Zn excess (765 mu M Zn for 4 days) by stimulating nutrient recycling and glycolysis, and production of defensive metabolites and proteins to maintain ion and redox homeostasis. Besides, adenosylhomocysteinase (AHCY) down-regulation may contribute to balanced transmethylations, and methionine salvage pathway appears important for the adaptation to Zn. Our results provide some new insight into a complex metabolic response of rice roots to Zn stress, which is related to both stress and defense mechanisms.

Automated summary

Our study revealed that high concentrations of zinc can affect the growth of rice seedlings and root cell death, but also stimulate glutathione synthesis, reduce levels of reactive oxygen species (ROS) and malondialdehyde. A total of 42 zinc-responsive proteins were identified, with proteins involved in redox regulation, defense responses, sulfur metabolism, and proteolysis being induced while those of energy production and cell wall biogenesis were decreased.