Are calcium ions and calcium channels involved in the mechanisms of Cu2+ toxicity in bean plants? The influence of leaf age

The influence of calcium channel blockers and ionophore on Cu2+-induced cha nges of the photosynthetic activity of runner bean plants (Phaseolus coccin eus L.) was investigated. Excess Cu2+ was applied to leaves by injection or via the roots to examine a short/local or a long time/systemic effect of t his metal, respectively. The changes in fluorescence parameters indicated t hat the mechanism of toxic action of Cu2+ ions on the photosynthetic appara tus was only partially connected with Ca2+ or Ca2+ channels. In young plant s Ca2+ diminished especially photochemical and nonphotochemical dissipative processes induced by short- and long-term influence of excess Cu2+. Blocki ng of Ca2+ channels did not change direct Cu2+ action on the photosynthetic activity, however, their opening distinctly intensified the inhibitory eff ect of the metal. After a longer accumulation period the effect of Cu2+ ion s did not change significantly due to modified Ca2+ penetration through mem branes (except that caused by La3+). Copper directly introduced into older leaves diminished only at its highest concentration the activity both of th e donor and acceptor sides of photosystem 2 (PS2) connected with Rfd decrea se and increase of LNU. A similar effect was observed also after a long-ter m Cu2+ action, but disturbances on the acceptor side of PS2 were observed o nly at a higher Ca2+ content in the nutrient solution. Ca2+ ions, particula rly after openning of channels, intensified direct inhibitory Cu2+ action o n the photosynthetic activity expressed by decreased values of F-v/F-0 and Rfd. Lanthanum and verapamil, at a lower Ca2+ content in the medium, decrea sed the photosynthetic activity of Cu2+-treated plants. This effect was als o seen after additional Ca2+ supply to the leaves.