Effect of aluminum on cytoplasmic Ca 2+ homeostasis in root hairs of Arabidopsis thaliana (L.)

Abstract

Aluminum inhibition of root growth is a major world agricultural problem where the cause of toxicity has been linked to changes in cellular calcium homeostasis. Therefore, the effect of aluminum ions (Al) on changes in cytoplasmic free calcium concentration ([Ca2+]c) was followed in root hairs of wild-type, Al-sensitive and Al-resistant mutants of Arabidopsis thaliana (L.) Heynh. Generally, Al exposure resulted in prolonged elevations in tip-localized [Ca2+]c in both wild-type and Al-sensitive root hairs. However, these Al-induced increases in [Ca2+]c were not tightly correlated with growth inhibition, occurring up to 15 min after Al had induced growth to stop. Also, in 32% of root hairs examined growth stopped without a detectable change in [Ca2+]c. In contrast, Al-resistant mutants showed little growth inhibition in response to AlCl3 exposure and in no case was a change in [Ca2+]c observed. Of the other externally applied stresses tested (oxidative and mechanical stress), both were found to inhibit root hair growth, but only oxidative stress (H2O2, 10 microM) caused a prolonged rise in [Ca2+]c similar to that induced by Al. Again this increase occurred after growth had been inhibited. The lack of a tight correlation between Al exposure, growth inhibition and altered [Ca2+]c dynamics suggests that although exposure of root hairs to toxic levels of Al causes an alteration in cellular Ca2+ homeostasis, this may not be a required event for Al toxicity. The elevation in [Ca2+]c induced by Al also strongly suggests that the phytotoxic action of Al in root hairs is not through blockage of Ca2(+)-permeable channels required for Ca2+ influx into the cytoplasm.

RNAi-Mediated Tocopherol Deficiency Impairs Photoassimilate Export in Transgenic Potato Plants

“…For instance, enhanced callose accumulation was observed in membranes and PD of pea roots in response to aluminum treatment, leading to the blockage of symplastic transport and inhibition of root elongation (Sivaguru et al, 2000). Interestingly, callose formation was strongly correlated with aluminuminduced oxidative damage to membrane lipids and changes in intracellular calcium homeostasis, suggesting a mechanistic link between lipid peroxidation and callose synthesis (Jones et al, 1998;Yamamoto et al, 2001). Because tocopherols are proposed to function effectively in the scavenging of lipid peroxy radicals responsible for the propagation of polyunsaturated fatty acid oxidation (Wefers and Sies, 1988;McKersie et al, 1990;Fryer, 1992;Munné-Bosch and Alegre, 2002), it is tempting to speculate that tocopherol deficiency may indirectly affect callose synthesis by increasing the extent of lipid peroxidation in the chloroplast membranes.…”

Aluminum Rapidly Depolymerizes Cortical Microtubules and Depolarizes the Plasma Membrane: Evidence that these Responses are Mediated by a Glutamate Receptor

“…In root hairs of Arabidopsis (Jones et al 1998a) and in the wheat root apex (Zhang and Rengel 1999), cytoplasmic calcium rises gradually, whereas in tobacco tissue culture cells calcium level actually decreases (Jones et al 1998b). Nevertheless, all of these reports sampled at intervals between 2 and 10 min, too low a temporal frequency to have recorded a calcium transient like the ones recently measured in Arabidopsis in response to glutamate (Dennison and Spalding 2000), or in other signal transduction cascades (e.g.…”

Evidence of Phytochrome Mediation in the Low-pH-Induced Root Hair Formation Process in Lettuce (Lactuca sativa L. cv. Grand Rapids) Seedlings

“…1997, aluminum (Jones et a/. 1995(Jones et a/. ,1998, phosphate (Bates and Lynch 1996), nitrate and pH (Ewens and Leigh 1985) and phytohormones , Ridge 1996, Cernac et a/.…”