Fig. 3. F-actin organization in expanding hypocotyl and root hair cells in wild-type Arabidopsis and crooked mutant. (Numbers given below scale bars are in µm.) (A) Wild-type hypocotyl cells displaying fine cortical F-actin mesh and longitudinally running subcortical F-actin cables connecting the cell ends. (B) Hypocotyl cells in crooked with thick, transversely linked F-actin bundles. (C) Dark grown, elongated wild-type hypocotyl cells with fine F-actin meshwork. (D) Aberrant actin bundling in crooked hypocotyl cells challenged to elongate rapidly. (E) Dark-grown crooked hypocotyl cells, a cell with one end displaying actin bundles (arrowhead). (F) Actin bundles at a crooked cell end mislocalize growth and create less elongating cells with bulged ends. Note that the two contiguous cells now break contact, leaving a gap in the hypocotyl epidermis (double-headed arrow). (G) A single hypocotyl epidermis cell in crooked curls up. Note that the site of dense actin (arrowhead) coincides with a less growing region whereas the outer more expanded curve has a thinner layer of actin. (H) A wild-type root hair with long actin bundles that stop just before the apex. (I,J) Sinuous root hairs from crooked with longitudinally extended actin bundles. Note that the regions where the actin bundle contacts and obscures the plasma membrane do not expand (arrowheads), whereas regions free from the bundle expand more. (K) A swollen root hair from crooked is filled with actin-bundles extending all the way to the tip (arrowhead). (L) A branched crooked root hair creates another region for tip growth. (M) Magnified view of the tip region in L shows dense actin at the tip (arrowhead), suggesting that inhibition of the growth of the original tip region (caused by dense actin) resulted in a new tip being formed.

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