Physiological and Ultrastructural Effects of Cadmium on Wheat (Triticum aestivum L.) Leaves

The effects of a 7-day exposure of 3-day-old wheat plants to increasing Cd concentrations are described, with special attention being given to chloroplast ultrastructural changes, chlorophyll fluorescence responses, chlorophyll and nutrient concentration changes as well as growth changes of the whole plant. The plants treated with 1 mM Cd showed symptoms of heavy metal toxicity. The root, shoot-leaf length and the root, shoot-leaf biomass progressively decreased with increasing Cd in nutrient solution and in 1 mM of Cd an almost complete inhibition of growth was found. Shoot-leaf Cd accumulation increased under Cd-treatments, while a Fe, Mg, Ca, and K decline in the above ground parts was observed. The growth reduction and the inhibition of chlorophyll content and photosynthesis observed in the upper plant parts seemed principally due to indirect Cd effects on the content of essential nutrients. Cadmium treatment was shown to damage the structure of chloroplasts, as manifested by the disturbed shape and the dilation of the thylakoid membranes. These ultrastructural changes suggest that Cd probably induced premature senescence.