Proteomic changes induced by potassium deficiency and potassium substitution by sodium in sugar beet

In this study, sugar beets (Beta vulgaris L.) were grown at different K+/Na+ concentrations: mmol/L, 3/0 (control); 0.03/2.97 (K-Na replacement group; T-rep); 0.03/0 (K deficiency group; T-def) in order to investigate the effects of K+ deficiency and replacement of K+ by Na+ on plant proteomics, and to explore the physiological processes influenced by Na+ to compensate for a lack of K+. After 22 days, fresh and dry weight as well as the Na+ and K+ concentration were measured and changes in proteomics were tested by 2D gel electrophoresis. Interestingly, Na+ showed stimulation in growth of seedlings and hindrance of K+ assimilation in T-rep. Significant changes were also observed in 27 protein spots among the treatments. These are proteins involved in photosynthesis, cellular respiration, protein folding and degradation, stress and defense, other metabolisms, transcription related, and protein synthesis. A wide range of physiological processes, including light reaction, CO2 assimilation, glycolysis, and tricaboxylic acid cycle, was impaired owing to K+ starvation. Compensating for the effect of K+ starvation, an increase in photosynthesis was also observed in T-rep. However, we also found a limitation of cellular respiration by Na+. Na+ is therefore in some ways able to recover damage due to K deficiency at protein level, but cannot functionally replace K as an essential nutrient