Low nitrate treatment promotes iron transportation from root to
shoot
Under Fe adequate conditions, we found that there was no significant
difference in total Fe content in new leaves and roots under either HN
or LN treatment. By contrast, under Fe deficient conditions, LN
treatment remarkably increased total Fe content both in newly growing
leaves and roots (Fig. 3a, b). In addition, the Fe content was higher in
stems of plants under LN-Fe treatment than that under HN-Fe treatment
(Fig. 3c). Nitrogen content analysis suggested that seedlings under
HN-Fe treatment had a higher nitrate and total nitrogen content than
that of LN-Fe treatment (Fig. S3a, b, c). Furthermore, gene expression
analysis found that the expression of MdFRD3 and MdMATE43 ,
which are associated with vascular Fe loading and unloading, were
dramatically increased by LN treatment (Fig. 3d, e). Early on in Fe
deficiency (1 day), LN treatment promoted the expression ofMdNAS1 (Fig. 3f), suggesting that LN-promoted iron transportation
might result from LN-induced upregulation of genes related with
Fe-chelator formation and transportation.