Lead-induced changes in plant morphology, cell ultrastructure, growth and yields of tomato
A pot experiment in plastic greenhouse was conducted to investigate the effect of Pb toxicity on development and ultrastructure of tomato (Lycopersicon esculentum Mill. cv. ZZ203) by four levels of Pb addition [0, 150, 450, and 900 mg/kg Pb in soil as Pb(NO3)]. The results showed that excess lead resulted in dwarf plants, wilting and misshapened leaves accompanied by less number, less numbers of the calyx, and longer-smaller fruits. At the same time, the condensed cytoplasm accompanied by the department of plasma from cell wall, swollen mitochondrial and chloroplast including thylakoid, fewer cristae in mitochondrial, loosely combined thylakoid to form askew grana, disruption plasma membrane and also followed with dilation organelles were all the typical toxic symptoms of Pb stress. Otherwise, plant biomass and fruit yields decreased as Pb increased: treatment or addition of Pb (150 mg/kg) decreased the aforestated parameters, but these differences did not approach significance at 5% level of probability; however, Pb (450 or 900 mg/kg) treatment, significantly decreased the aforementioned parameters. Excess lead (900 mg/kg) inhibited biomass and fruit yields by 71 and 51% as compared to the zero Pb control treatment respectively. Concentration of Pb in plant tissues decreased in the following order: fruits, leaves, stems and roots.
Key words: Lead, tomato, plant morphology, ultrastructure, growth, yield.