Metabolism of nucleic acid and changes of cell ultrastructure in stem apex o tea seedling induced by Cd²⁺

Tea seedlings were treated for 12 days by different concentrations of culture solution with Cd²⁺. The results show that the ｂbiomass of the seedlings is not affected when Cd²⁺²⁺ concentration and treatment time when Cd²⁺ concentration is ≥0.10 mmol/L.The content of nucleic acid increases at Cd²⁺ level of 0.05mmol/L and decreases at Cd²⁺ levell ranging from 0.10mmol/L to 0.50mmol/L. RNA is more sensitive toCd²⁺ stress compared with DNA. The Rnase activity increases at Cd²⁺ level ranging from 0.00mmol/L to 0.10mmol/L and decreases at Cd²⁺ level ranging from 0.25mmol/L to 0.50mmol/L. The nucleus ultrastructure changes progressively with the increase of Cd²⁺ concentration. When seedlings are treated with 0.05mmol/L Cd²⁺, the nucleolus disintegrates and the chromatin condenses, the perinuclear spaces are slightly dilated. The deeply expanded perinuclear membrane contains nuclear materials at Cd²⁺ level of 0.10mmol/L. More serious damage is shown in the nucleus with higher Cd²⁺ concentrations, such as deformation of nucｌeus, shrinking ｏof nucleus, scattering of condensed chromatin and eventually disruption of nuclear membrane.