MF Organization Is Altered in arp2-2 Cells during Salt Stress MF Organization Is Altered in arp2-2 Cells during Salt Stress.(A) MF organization of cotyledon pavement cells of the wild type (WT) and arp2-2. MF Organization Is Altered in arp2-2 Cells during Salt Stress.(A) MF organization of cotyledon pavement cells of the wild type (WT) and arp2-2. Seven-day-old seedlings of transgenic wild type or arp2-2 harboring Pro35S:fABD2-GFP were treated with liquid MS media without or with 200 mM NaCl for the indicated times and seedlings were visualized with a confocal microscope. At least 10 independent leaves were analyzed in three experiments with similar results. Bar = 20 μm for all fluorescence images.(B) Percentage of wild-type and arp2-2 mutant cells with polymerized MF organization. Seven-day-old seedlings of transgenic wild-type and arp2-2 plants expressing Pro35S:fABD2-GFP were treated with liquid MS media without or with 200 mM NaCl for the indicated times. With extended NaCl treatment, MFs in arp2-2 became more unstable than in the wild type. Values represent means ± se; n > 50. *P < 0.05 and **P < 0.01 by Student’s t test.(C) The extent of filament bundling (skewness) of pavement cells. Skewness in arp2-2 was higher than in the wild type after 200 mM NaCl treatment for 16 h. Values represent mean ± se; n = 35. *P < 0.05 by Student’s t test.(D) Average filament density of wild-type and arp2-2 pavement cells. The filament density in arp2-2 was less than in the wild type, and the actin filaments depolymerized after 200 mM NaCl treatment for 24 h or longer. Values represent mean ± se; n > 60. *P < 0.05 and **P < 0.01 by Student’s t test.(E) MF organization of hypocotyl cells of the wild type and arp2-2. Seven-day-old seedlings of transgenic wild type or arp2-2 expressing Pro35S:fABD2-GFP were treated with liquid MS media without or with 200 mM NaCl for the indicated times, and seedlings were visualized with a confocal microscope. At least 20 independent hypocotyls were analyzed in three experiments with similar results. Bar = 5 μm for all fluorescence images.(F) Percentage of wild-type and arp2-2 mutant hypocotyl cells with polymerized MF organization. Seven-day-old seedlings of transgenic plants expressing Pro35S:fABD2-GFP in the wild type and arp2-2 mutant were treated with liquid MS media without or with 200 mM NaCl for the indicated times. When treatment time reached 3 h, MFs in arp2-2 became more unstable than in the wild type. Values represent mean ± se; n > 80. **P < 0.01 by Student’s t test.(G) The extent of filament bundling (skewness) of hypocotyl cells. Values represent mean ± se; n > 80. *P < 0.05 by Student’s t test.(H) Average filament density of wild-type and arp2-2 hypocotyl cells. The filament density in arp2-2 was less than in the wild type, and the actin filaments depolymerized after 200 mM NaCl treatment for 24 h or longer. Values represent mean ± se; n > 80. *P < 0.05 by Student’s t test.[See online article for color version of this figure.] Yi Zhao et al. Plant Cell 2013;25:4544-4559 ©2013 by American Society of Plant Biologists