Influx carrier mutants show impaired xylem differentiation in Arabidopsis shoot stem.

(A-B) VB magnification of a shoot basal cross section for WT (A, C and E) and aux1lax1lax2lax3 quadruple mutant (B, D and F) 14-weeks old plants grown in short day conditions. Light blue dots indicate undifferentiated cell layers in procambium tissue between phloem and xylem differentiated cells. First differentiated xylem cell is indicated by white arrow. The undifferentiated cell layers comprise both the procambial cells and the meristematic xylem cells (round cells with undifferentiated walls between the procambium and the xylem). Note that above the procambial cells appear some undifferentiated cells with different shape than the procambial cells. This round shape is more characteristic from xylem cells while the cell walls are not differentiated. Therefore, we quantify them as undifferentiated cells, which can comprise both, procambial and meristematic xylem cells. White squares highlight interfascicular fiber cells. Scale bar: 100 μm. (G) Frequency distribution of the number of undifferentiated cell layers, for WT and aux1lax1lax2lax3 mutants (n = 24 VB).