EFFECTS OF AL, RARE-EARTH ELEMENTS, AND OTHER METALS ON NET CA-45(2+)UPTAKE BY AMARANTHUS PROTOPLASTS

Aluminium has recently been shown to interfere with Ca2+ influx into A maranthus protoplasts by binding to the verapamil-specific site and th us blocking Ca2+ channels. To further elucidate the mechanism of Al-re lated blockage of Ca2+ channels, short-term net Ca-45(2+) uptake by Am aranthus tricolor protoplasts was monitored from uptake media prepared to test the influence of pH, Al and various other metal ions. Gadolin ium and lanthanum (well-known Ca2+-channel blockers) appeared to be mo re powerful inhibitors of net Ca2+ uptake than Al at both pH levels te sted (4.5 and 5.5). Aluminium counteracted the inhibition due to La. N o interaction was noted between Al and Gd. Another rare earth element tested, cerium, showed the same pattern of inhibition of net Ca2+ upta ke regardless of the presence or absence of Al at both pH values. Comp ared to Al, several other metals known to inhibit root growth and elon gation (rhizotoxicity is also an early symptom of Al stress) were eith er less inhibitory to net Ca2+ uptake [indium and especially chromium( III)] or did not affect net Ca2+ uptake at all (scandium).