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Mutant alleles of Arabidopsis RADIALLY SWOLLEN 4 and 7 reduce growth anisotropy without altering the transverse orientation of cortical microtubules or cellulose microfibrils

¹ Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211-7400, USA
² Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra ACT 2601, Australia

View larger version (94K): [in a new window]   Fig. 1. Light micrographs showing morphology and histology of rsw4 and rsw7 roots. (A-C) Paired images of a roots grown under (left-hand image) the permissive treatment (8 days at 19°C) and under (right-hand image) the restrictive treatment (6 days at 19°C followed by 2 days at 30°C). (A) Wild type; (B) rsw4; (C) rsw7. Bar: 100 µm. (D-L) Cross sections of roots within the region of maximal diameter stained with PAS to show cell walls: (D-F) Wild type; (G-I) rsw4; (J-L) rsw7. The left hand column (D,G,J) shows the anatomy of plants grown under the permissive treatment, the center column (E,H,K) the restrictive treatment, and the right-hand column (F,I,L) the permissive treatment supplemented with 10 µg/ml aphidicolin for the 2 days at 30°C (wt and rsw7) or for only the second day (rsw4). Bar: 50 µm.

View larger version (17K): [in a new window]   Fig. 2. Growth kinetics of rsw4 and rsw7 roots. Seedlings were transferred to 30°C (time zero on the x-axis) after 6 days at 19°C. (A,B) Elongation rate; (A) mean±s.d. of 10 seedlings or (B) mean±s.e.m. of 3-6 plates. (C) Root diameter; mean±s.d. of 10 seedlings.

View larger version (23K): [in a new window]   Fig. 3. Tissue areas of rsw4 and rsw7 roots. Area per tissue for rsw4 at 19°C (white bars), rsw4 at 30°C (black bars), rsw7 at 19°C (light-gray bars) and rsw7 at 30°C (dark-gray bars) expressed as the percent increase of the area in wild type grown at 19°C. All treatments were for 8 days, with 30°C for the final 2 days. Data are means±s.e.m. of 4 roots with 4 sections per root.

View larger version (102K): [in a new window]   Fig. 4. Cortical microtubules of wild type, rsw4 and rsw7 in the elongation zone (wild type) or swollen region of the root. (A-C) Cortical microtubules in epidermal cells imaged with confocal microscopy. (D-F) Cortical microtubules in root cortex imaged in longitudinal methacrylate sections. (A,D) Wild type, (B,E) rsw4 and (C,F) rsw7 plants grown at 19°C for 6 days and transferred to 30°C for 2 days. Bars: 10 µm.

View larger version (19K): [in a new window]   Fig. 5. Analysis of monosaccharides in wild type, rsw4, and rsw7 cell walls. The levels are expressed per mg of cell wall dry weight. Cellulosic glucose is the material that is insoluble in boiling trifluoroacetic acid. Data are mean of 4 replicate determinations±s.d. Significance was tested with two-tailed, paired t-tests, mutant versus wild type, and indicated when equivalence of means was rejected by *P<0.05, **P<0.01 or ***P<0.001.

View larger version (96K): [in a new window]   Fig. 6. FESEM micrographs of the innermost cell wall layer of wild type, rsw4 and rsw7 plants in the elongation zone (wild type) or swollen region of the root. (A-C) Longitudinal-radial cell walls with the long axis of root parallel to the long axis of the page. (A) Wild type, (B) rsw4 and (C) rsw7, grown at 19°C for 6 days and transferred to 30°C for 2 days. (A-B) PEG sections, (C) cryo-ultramicrome. Bar: 100 nm.

View larger version (94K): [in a new window]   Fig. 7. Polarized-light micrographs of longitudinal sections of the elongation zone (in the wild type) or swollen region of the root in rsw4 and rsw7. The transmission axes of analyzer and polarizer are shown by the white right-angle in (A). (A,C,E) The compensator was rotated to a positive angle, and (B,D,F) to a negative angle; the orientation of the white line in the two upper panels (A,B) shows the direction of the optical axis of birefringent elements (i.e., microfibrils) that would produce regions of the image brighter than background. (A,B) A section from wild type, (C,D) rsw4 and (E,F) rsw7 shown with each compensator setting. Seedlings were grown as for Fig. 4. The left-hand and right-hand panels were photographed with identical microscope settings and processed identically for reproduction. Bar: 25 µm.

View larger version (20K): [in a new window]   Fig. 8. Birefringent retardation versus distance from the quiescent center in cell walls of wild-type and mutant roots. (A,B) Wild type; (C) rsw4; (D) rsw7. (A,C,D) Data for seedlings grown for 8 days at 19°C (open circles), and seedlings grown for 6 days at 19°C and transferred to 30°C for 2 days (filled circles). (B) 8-day wild-type roots treated with 1 µM DCB for 12 hours at 30°C (filled triangles), and 8-day rsw1 roots exposed to 30°C for 12 hours (filled squares). (B,C,D) The dotted line indicates the wild-type 30°C data from A. For each treatment, three sections from four roots were sampled, and symbols are means±s.d. of six to 21 cell walls located within 50 µm of the x-axis value.

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