Stress indications in copper- and nickel-exposed Scots pine seedlings

Scots pine nursery seedlings were planted in pots, five seedlings per treat ment, and placed in an experimental field at the University of Oulu in nort hern Finland at the beginning of June 1997. Copper and nickel sulphates wer e mixed with forest mineral soil before seedling planting. The metal levels ranged from 0 to 25 mg Ni kg(-1) dry soil and 0 to 50 mg Cu kg(-1) in dry soil and in combinations of both metals. Current year's needles for element analyses, EDS microanalyses, microscopy and glutathione and peroxidase act ivity analyses were collected from 1-5 seedlings per treatment in September . Seedling biomass in controls, Cu25 and Cu50 differed significantly from t he Ni25Cu50 treatment. The root/shoot ratio was highest in the Ni5 treatmen t, indicating good root growth, though the roots were visibly healthier in the Cu25 treatment than in the Ni5 treatment. At higher Ni levels, the cond ition of roots deteriorated. The proportion of plasmolysed mesophyll cells was highest in the Ni25 treatment. Copper-treated seedlings did not suffer from Cu stress, because no severe injuries were seen in either the roots or the needles in Cu-exposed seedlings. The needle concentrations of Cu incre ased only slightly due to treatments. Ni accumulation in needles increased with increasing concentrations in soil. Needles of Cu-treated seedlings had less oxidized glutathione than those of Ni-treated seedlings, but the root s had higher, not significantly, peroxidase activity levels. Light-colored, swollen thylakoids were occasionally observed in the Ni25Cu50 treatment, i ndicating some interaction between Ni and Cu. Ni seemed to cause more oxida tive stress to the seedlings than copper, which was manifested as a decreas ed GSH level and an increased proportion of GSSG in the Ni treatments. Copp er together with nickel strongly decreased root growth, the root/shoot rati o being lowest in the Ni25Cu50 treatment. (C) 2000 Elsevier Science B.V. Al l rights reserved.