Ultrastructural damage in tomato plants exposed to chromium III

摘要

The study aimed to investigate the short-term effects of Cr on the ultrastructure of root, stem and leaf cells of tomato plants (Solanum lycopersicum L.), and to verify the compartmentalization of the transition metal. Tomato seedlings were grown in an environmental chamber maintained at 25 ±1°C, with relative humidity of 70% and a 12 h photoperiod, in full-strength nutrient solution containing 25 or 50 mg L~(-1) of Cr(III), while control plants were cultured in the absence of Cr. An electron probe X-ray microanalyzer equipped with a wavelength dispersive spectrometer was used in association with transmission electron microscopy in order to localize Cr deposits. In tomato roots Cr deposits were concentrated mainly in the cell walls, while in stems and leaves the deposits could be observed in the cells walls as well as in vacuoles, suggesting that these compartments act as barriers against metal phytotoxicity. Plants exposed to Cr presented leaves containing abnormally shaped chloroplasts, with reduced numbers of grana and atypical thylakoids, whereas the mitochondria presented reduced numbers of cristae. These Cr-induced alterations result in the diminution of photosynthetic and respiratory activities with harmful consequences to plant health. The microanalytical methods employed in this study have shed new light onto the possible causes of Cr phytotoxicity. Such knowledge is valuable in understanding the mechanisms employed by plants to circumvent the uptake and transport of potentially toxic metals.