Calcium influx at the tip of growing root-hair cells of Arabidopsis thaliana

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Abstract
The role of extracellular Ca2+ in root-hair tip growth has been investigated in Arabidopsis thaliana (L.) Heynh. Root-hair length was found to be dependent on the concentration of Ca2+ in the growth medium, with maximum length achieved at [Ca2+] of 0.3–3.0 mM. Using a non-intrusive calcium-specific vibrating microelectrode, an extracellular Ca2+ gradient was detected at the tips of individual growing root-hair cells. The direction of the gradient indicated a net influx of Ca2+ into root-hair cells. No gradient was detected near the sides of the root hairs or at the tips of non-growing root hairs. When root hairs were exposed to the Ca2+-channel blocker nifedipine, tip growth stopped and the extracellular Ca2+ gradient was abolished. These results indicate that Ca2+ influx through plasma-membrane Ca2+ channels is required for normal root-hair tip growth.