Fig. 2. GFP-mTalin aided visualization of F-actin organization in trichome and cotyledon-epidermal cells of wild-type Arabidopsis and crooked mutant (n, nucleus; numbers given below scale bars are in µm). (A) A wild-type trichome that has initiated branches and is ready to embark on a rapid expansion phase. Trichomes in crooked exhibit a similar F-actin organization at this stage, with major actin accumulations as shown (arrowheads). (B) Wild-type trichomes where branches have started extending maintain dense F-actin at the tips and junctions of branches (arrowheads), while elongated F-actin cables connecting regions of dense actin start to become prominent. (C) A crooked trichome at a stage comparable with that of wild type in B displays an increase in dense F-actin bundles throughout the cell, resulting in more intracellular areas being covered by dense actin (arrowheads). Note that the cell starts thickening around its mid region while the uppermost branch maintains a rounded tip, suggesting less extension of the flanks. (D) A slightly more advanced stage of development in a crooked trichome shows massive actin bundling and the organization of a characteristic wide-polygonal mesh. Note that in A-D, while dense actin can be easily visualized, areas with very fine and difficult to resolve F-actin meshwork are only visible as a diffuse green fluorescence. (E) A region of a mature wild-type trichome displaying predominantly longitudinally oriented (arrows) F-actin bundles. (F) A mature crooked trichome with predominantly transversely arranged, cross-connected, thick actin bundles appears subdivided into numerous polygonal compartments (arrowhead). Note that the crooked trichome has not been able to expand well and one of the branches `b' is visible as a short unextended spike. (G) Expanding wild-type cotyledon epidermis displaying the typical puzzle-shaped cells with prominent lobes. A fine, diffuse cortical F-actin and thick F-actin cables (e.g. arrowheads) connecting strategic points within each cell are seen. (H) A comparative view of the cotyledon epidermis in crooked shows thickly bundled F-actin (arrowheads) and impaired lobe formation. (I) A higher magnification of wild-type cotyledon epidermal cells shows the occurrence of dense actin specifically at lobe sinuses (e.g. arrowheads), while other areas of the cell possess relatively finer F-actin organization. (J) A cotyledon epidermal cell in crooked with no lobes displays a general distribution of bundled actin. The arrowheads indicate thicker bundles.

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