Calcium modifies Cd effect on runner bean plants

The effect of different Ca concentrations in the growth medium on the toxic ity of 25 mu M CdSO4 was studied in runner bean plants (var. Piekny Jas) at two different growth stages of primary leaves. In young plants growing in a medium with low level of Ca a treatment with Cd for 12 days resulted in C a accumulation in roots, a strong reduction of the leaf area, a decreased m onogalactosyl diacylglycerol/digalactosyl diacylglycerol ratio and efficien cy of the photosynthetic apparatus. In leaves of older plants growing under the same conditions, and surviving Cd treatment, a high accumulation of Ca but a low one of Cd, chlorosis of leaves, a decrease of the ratio monogala ctosyl diacylglycerol/digalactosyl diacylglycerol and photosynthetic activi ty were shown. At a high level of Ca in the nutrient medium plant roots sho wed a remarkably high specificity to accumulate Cd but the toxic effect of the metal on plant growth parameters and content of pigments was decreased. No changes were observed in the level of galactolipids, but changes in flu orescence quenching were recorded. Calcium deficit enhanced the effect of C d toxicity, including primary photochemistry, whereas excess Ca reduced tox ic effects, while it is increasing the nonphotochemical quenching of excita tion energy. (C) 1998 Elsevier Science B.V. All rights reserved.