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Abstract
Changes in plant growth and in pigment content were studied in tomatoes (Lycopersicon esculentum), cultivated on soils, polluted with arsenic (As) in sublethal doses (15, 25, 50, and 100 mg kg−1). An elongation of root system and increase of stem height and stem weight was observed at lower arsenic concentration (15 and 25 mg kg−1) especially at 15 mg kg−1. The higher element concentrations (50 and 100 mg kg−1) lead to a decrease in growth of both the vegetative and root system. An index of depression (ID), calculated on the base of morphological parameters shows a stimulation of plant growth in case of 15 mg kg−1 As in soil and depression of plant growth in case of 50 and 100 mg kg−1 As in soil. No significant change of ID was observed in the case of 25 mg kg−1 As in soil. The lower As doses (15 and 25 mg kg−1) stimulated synthesis of pigments may be as a result of defense mechanism of plants to the applied stress, while the higher ones (50 and 100 mg kg−1) decrease it. The significant decline of the pigments in plants treated with higher doses is an indication of poor conditions of those plants and the lack of adaptive adjustment to high As levels. All these changes could be an indication of arsenic toxicity on the plants. The As concentration 25 mg kg−1 in soil appeared to be a threshold value over which the element causes some toxic changes in plants.