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

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 μM of Zn in a hydroponic set-up after 4-day exposure. 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. 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. Roots of O. sativa seedlings could tolerate certain Zn excess (765 μM 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.