EFFECTS OF ZINC TOXICITY ON SEED GERMINATION AND PLANT GROWTH IN TOMATO (Lycopersicon esculentum Mill.)

In this study, Hoagland solutions containing different amounts of Zn (1, 3, 5, and 7 mM ZnCl2) were used as growth medium to comprehend the possible effects of zinc toxicity on seed germination and plant growth in tomato. The highest zinc accumulation was obtained in the roots of the plants treated with 7 mM. The zinc concentration in the vegetative parts was highest in roots but lowest in cotyledons. To elucidate the physiological consequences of this element, anthocyanin, carotenoid, chlorophyll, and total soluble protein contents as well as the level of peroxidase enzyme activity were measured in roots, hypocotyls, and cotyledons of 8 day-old plants. 1 mM of ZnCl2 was found to have induced germination of tomato seeds; however, concentrations above this value, especially 5 mM, were inhibitory. Root and hypocotyl development was induced in 1 mM, but significantly retarded in the media containing 3-7 mM. Total soluble protein contents were increased in 1-5 mM, especially in roots and hypocotyls, but at 7 mM were significantly reduced. Furthermore, concentrations higher than 1 mM resulted in enhancement of peroxidase activity. Similarly, carotenoid and chlorophyll contents of cotyledons of the plants grown in 1-5 mM were significantly higher than the ones grown in control medium. Our results suggested that tomato plants were able to tolerate zinc between 3-5 mM but excess Zn showed toxic effects on tomato seedlings.