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.