The sac9-1 Mutant of Arabidopsis thaliana

The sac9-1 mutant in Arabidopsis thaliana is slow growing and dwarfed (Fig. 1)
	Figure 1. Wild-type Columbia strain of Arabidopsis thaliana (left) and the sac9-1 mutant (right).

Guard cells in sac9 mutants are flaccid, and epidermal cells accumulate purple anthocyanin (Fig. 2)
	Figure 2. Guard cells of the wild-type Columbia strain of Arabidopsis thaliana (left) and the sac9-1 mutant (right).

The sac9 phenotype can be mimicked by subjecting wild-type plants to osmotic stress (Fig. 3.)
	Figure 3. Ten-day-old plants of wild-type Columbia strain of Arabidopsis thaliana grown with (left) or without (middle) 50 mM NaCl and the sac9-1 mutant grown without NaCl (right).

The SAC9 gene encodes a putative phosphoinositide phosphatase (PI phosphatase) and the plants accumulate PtdIns(4,5)P2 and Ins(1,4,5)P3:

Accumulation of PtdIns(4,5)P2 in yeast causes an increased rate of endocytosis; using the lipid-binding dye FM4-64 we observed an increased rate of membrane endocytosis in sac9 mutants as compared to wild-type plants (Figure 4). Movement of internal vesicles is also increased in sac9-1 mutants as compared to wild-types.
	Figure 4. Fluorescence micrographs of wild-type Columbia strain of Arabidopsis thaliana (left) and the sac9-1 mutant (right) stained with the lipid-binding dye FM4-64.

MOVIES of vesicle movement in the root
hairs of Arabidopsis thaliana Col-0 and sac9
mutant. Notice that the rate of movement of
vesicles is much higher in the sac9 mutant.
For ease of comparison, we have circled a single
vesicle for the first half of each movie.

click here for Col-0

click here for sac9