Proteome changes caused by nutrient conditions
Proteomics analyses were carried out, and the full list of significant proteins in tabulated in Table S2. A summary showing proteins involved in primary CNS metabolism is provided in Table 1. As expected, in leaves, many proteins involved in photosynthesis and photorespiration (Rubisco, Rubisco activase, phosphoribulokinase, serine glyoxylate aminotransferase, etc.) were significantly affected by K conditions, showing the effect of K availability on the development of the photosynthetic machinery. Importantly, key enzymes of catabolism were more abundant under low K (isocitrate dehydrogenase, aconitase, malic enzyme, pyruvate dehydrogenase, etc.) showing the up-regulation of respiration. Also, low K was associated with an increase in carbamoyl phosphate synthase (required for arginine and polyamine synthesis), and a decrease in pyruvate kinase. The decrease in pyruvate kinase content reflects the down-regulation of this K-dependent metabolic step when K is limiting. In roots, a small number of proteins were significant, and included also pyruvate kinase and proteins directly involved in N assimilation (nitrate transporters, glutamine synthetase), all decreased under low K.
High Ca impacted negatively on pyruvate kinase and several enzymes of photosynthesis in leaves. In roots, only two enzymes had aP -value above the Bonferroni threshold and these included pyruvate kinase (decreased at high Ca). Putrescine addition caused an increase in the content of enzyme involved in photosynthesis and glucose oxidation (glucose/ribitol dehydrogenase and glucose 6-phosphate dehydrogenase) in leaves. In roots, putrescine addition caused a decline in proteins involved in nitrogen assimilation: nitrate transporters, aspartate aminotransferase and glutamine synthetase.