Fluorescence resonance energy transfer-sensitized emission of yellow cameleon 3.60 reveals root zone-specific calcium signatures in Arabidopsis in response to aluminum and other trivalent cations.

Fluorescence resonance energy transfer-sensitized emission of the yellow cameleon 3.60 was used to study the dynamics of cytoplasmic calcium (Ca(2+)) in different zones of living Arabidopsis (Arabidopsis thaliana) roots. Transient elevations of Ca(2+) were observed in response to glutamic acid (Glu), ATP, and aluminum (Al(3+)). Each chemical induced a Ca(2+) signature that differed among the three treatments in regard to the onset, duration, and shape of the response. Glu and ATP triggered patterns of Ca(2+) increases that were similar among the different root zones, whereas Al(3+) evoked Ca(2+) transients that had monophasic and biphasic shapes, most notably in the root transition zone. The Al(3+)-induced Ca(2+) increases generally started in the maturation zone and propagated toward the cap, while the earliest Ca(2+) response after Glu or ATP treatment occurred in an area that encompassed the meristem and elongation zone. The biphasic Ca(2+) signature resulting from Al(3+) treatment originated mostly from cortical cells located at 300 to 500 mu m from the root tip, which could be triggered in part through ligand-gated Glu receptors. Lanthanum and gadolinium, cations commonly used as Ca(2+) channel blockers, elicited Ca(2+) responses similar to those induced by Al(3+). The trivalent ion-induced Ca(2+) signatures in roots of an Al(3+)-resistant and an Al(3+)-sensitive mutant were similar to those of wild-type plants, indicating that the early Ca(2+) changes we report here may not be tightly linked to Al(3+) toxicity but rather to a general response to trivalent cations.