*2.9. MdSAP15-Overexpressing Arabidopsis Seedlings Have Improved Physiological Traits Associated with Osmotic Stress Tolerance When Compared with "Col" Wild Type*

For further investigation of this *MdSAP15*-mediated enhancement of tolerance to osmotic stress, we measured relative electrolyte leakage (REL) and concentrations of chlorophyll, proline, and malondialdehyde (MDA), all of which are important markers of such tolerance. Under normal growing conditions, we did not observe any obvious differences in REL. However, in response to mannitol exposure, REL values were significantly higher in "Col" seedlings than in the transgenics (Figure 7E). Levels of chlorophyll and proline were similar between "Col" and OE plants under control conditions, but were higher in the transgenics after they were treated with 200 mM of mannitol (Figure 7F,G). Furthermore, MDA concentrations did not differ among genotypes under normal conditions, but were lower in the overexpressed (OE) lines than in the WT following mannitol treatment (Figure 7H). These results suggested that the overexpression of *MdSAP15* in *Arabidopsis* seedlings leads to enhanced osmotic stress tolerance.
