sitl1 mutant alters root development
The root morphology analysis revealed a significant decrease in lateral root number, average lateral root length, and sum of lateral root length but had no significant change on lateral root density in thesitl1 compared to WT under normal condition (Figure 2a-e). In addition to the primary root growth, the lengths of root immature zone and mature zone in the sitl1 decreased by 0.79-fold and 0.77-fold compared to WT, respectively. Also, the primary root width of thesitl1 decreased but the lateral root width was not significantly changed compared to WT (Figure 2h,i). Under the deionized water-grown condition, all significant changes in the root growth of sitl1were not observed (Figure 2b-i).
To determine whether the reduction in primary root growth was due to decreased cell proliferation or cell elongation in the sitl1 , the root cell number and the length of epidermis in the apical meristem and the basal meristem were compared between the sitl1 and WT (Figure 3). The measurement of the cell number in root meristem zone showed that the average cell number in the apical meristem significantly decreased by 0.87-fold in the sitl1 but cell number in the basal meristem was not changed compared to that of WT (Figure 3b,c). Total cell number in root meristem was 0.9-fold lower than WT (Figure 3d). The length of the apical, basal and total meristem in the sitl1 was 0.91-, 0.78-, and 0.82-fold shorter than that in the WT, respectively (Figure 3e-g). These decreases in length were due in part to a decrease in cell number within the apical meristem (Figure 3b,e). Next, cell length was measured to verify if the decreased basal meristem length in thesitl1 was due to slow rates of the cell elongation within the basal meristem zone. Indeed, average cell length and width in the basal meristem, and average cell width in the apical meristem decreased by 0.75-, 0.79-, and 0.75-fold respectively, whereas average cell length in the apical meristem was not significantly changed in the sitl1compared to WT (Figure 3h,i). Furthermore, individual cell size (e.g. length, width and area) of the root exodermal cell in the mature root zone also decreased significantly, relative to control lines (Figure 3j-m). These results suggest that the reduced ability of Mg2+ uptakes in the sitl1 likely contributes to the decreased the rate of cell proliferation and cell elongation resulting in growth reduction in root tissues.