Key Mechanisms Leading to the Contrasting Nitrogen Deficiency Response in a Pair of Potato Cultivars
Nitrogen deficiency is known as one of the major limitations in crop productivity and the yield losses caused by inadequate N supply are far greater than those caused by a deficiency in other macronutrients. In the case of potato, due to its low capability of N retraction from the soil, there is a higher demand for fertilization and therefore a higher negative impact on the environment. The aim of the presented thesis was to elucidate metabolic pathways, and candidate proteins determining the contrasting responses of the potato cultivars ‘Lambada’ and ‘Topas’ to N deficiency. The potato proteome was analyzed using mass spectrometry-based approaches, in respect to the crude root proteome, with an additional focus on the proteins of the plasma membrane and on the changes in the phosphorylation pattern. The most promising candidate proteins were further validated by using enzymatic assays, Western blotting and A. thaliana mutant plants. In response to N deficiency the tolerant cultivar ‘Topas’ showed higher accumulation of proteins participating in N assimilation, C metabolism as well as in protein synthesis and degradation, together with a stable growth and higher N content. The study of the plasma membrane composition revealed a higher abundance of the nitrate transporter NRT2.1 as well as two isoforms of aquaporins. The relevance of aquaporins in the response to N deficiency was confirmed by experiments with Arabidopsis mutants, which showed significantly reduced N content in the leaves. The main conclusion of the study was, that under non-limiting conditions, the sensitive cultivar used all the applied N to produce biomass, whereas the tolerant cultivar produced N-containing compounds and more proteins. When N is limited, the sensitive cultivar’s ability to grow rapidly decreases. In contrast, the tolerant cultivar uses the NRT2.1 as well as aquaporins for more efficient N uptake but it also consumes the accumulated resources to adapt to the lower N conditions.