Fig. 4.

Comparative analyses of UPR and cell death in the roots of WT Arabidopsis and hsn1 seedlings (10 DAG). (A) UPR in the roots (Upper) and root tips (Lower) was revealed by staining of the biomarker BiP–GUS that is frequently used in monitoring UPR in eukaryotic cells (21, 22). BiP–GUS was transferred into WT and hsn1 backgrounds through genetic crossing. The marker-tagged lines were cultured on modified MS media with a constant level of NO₃⁻ (20 mM) but rising concentrations of NH₄⁺. The arrow indicates the root apical meristematic region. (Bars: Upper, 1 mm; Lower, 0.1 mm.) (B) WT Arabidopsis and hsn1 were grown on NO₃⁻ + NH₄⁺ or NO₃⁻ medium. Cell death in the roots was revealed by the blue precipitates produced by histochemical staining with Evans blue. (Bars: 0.2 mm.)