Candidate proteins involved in the adaptation of potato to N deficiency
A protein identified as NRT2.1 (accession number- 400031304) increased 8.2-fold in ‘Topas’ and decreased in ‘Lambada’. Three isoforms of the PM H+-ATPase (400083041, 400065168, 400010497) increased between 1.9- and 4.1-fold in ‘Topas’, while in ‘Lambada’ their abundance remained unchanged. Four other proteins also displayed this behavior, including a sugar carrier protein C (400057709) and two ABC transporters (400018820- ABCB family member, 400046727- ABCA family member). In addition, two proteins belonging to the PM intrinsic protein (PIP) aquaporin subfamily increased in ‘Topas’ compared to ‘Lambada’ under N deficiency. The aquaporin isoforms PIP1;1 (400012780) and PIP1;3 (400032134) were, respectively, four and 2.5 times higher in N-deficient ‘Topas’, but remained unchanged in ‘Lambada’ (Fig. 2, marked with asterisks). Additionally, both isoforms were more abundant in ‘Topas’ (1.6 and 1.8-fold in PIP1;1 and PIP1;3, respectively) than in ‘Lambada’ under N-sufficient conditions. As aquaporins have not only proved to play an important role in water conductance, but also to facilitate the transport of other small uncharged solutes such as urea or ammonia (Jahn et al., 2004; Loque, Ludewig, Yuan, & von Wiren, 2005), we further investigated the transcript levels of the PIP1;1 andPIP1;3 genes during N deficiency and their potential role in N uptake.