Distribution of G-actin is Related to Root Hair Growth of Wheat

Background and Aims Actin distribution in root hair tips is a controversial topic. Although the relationship between Ca2+ gradient and actin dynamics in plant tip-growth has been a focus of study, there is still little direct evidence on the exact relationship in root hair tip-growth.Methods G-actin was labelled by fluorescein isothiocyanate-DNase I. F-actin was labelled by tetramethylrhodamine isothiocyanate-phalloidin. Actin in root hairs of Triticum aestivum (wheat) was investigated using confocal laser-scanning microscopy.Key Results Thick F-actin bundles did not extend into a region of approx. 5-10(mu)m from the tip of the growing root hairs, although they gave off branches of fine actin filaments in the hair tips. A tip-focused G-actin gradient was shown at the extreme apex of growing root hairs. In full-grown wheat root hairs, the tip-focused G-actin gradient disappeared while the thick F-actin bundles extended into the tips. BAPTA-AM, a Ca^2+ disruption agent, also caused the tip-focused G-actin gradient to disappear and the diffuse Factin bundles to appear in the tips of wheat root hairs.Conclusions These results suggest that the tip-focused gradient of intracellular G-actin concentration at the extreme apex may be essential for root hair growth, and that preserving the tip-focused gradient needs a high Ca^2+ concentration in the root hair tips.