| Summary: | 碩士 === 國立臺灣大學 === 農藝學研究所 === 89 === The aim of this thesis was to study cadmium toxicity of rice seedlings (Oryza sativa L. cv. Taichung Native 1, TN1 and Oryza sativa L. cv. Tainung 67, TNG67). We intvestigated (a) the relationship beween ethylene, abscisic acid (ABA) and cadmium toxicity of rice seedlings, (b) the effects of CdCl2 on the quantitative and qualitative changes of proteins in leaves of rice seedlings and (c) the relationship between the accumulation of NH4+ and cadmium toxicity of the rice seedlings.
Leaves of TNG67 rice seedlings were found to be more tolerant to CdCl2 than those of TN1 rice seedlings. The degree of Cd tolerance is unlikely related to ethylene or water deficit, but is more likely related to ABA. This conclusion was based on the observations that (a) CdCl2 treatment resulted in an increase in ABA content in leaves of TNG67 rice seedlings, which show CdCl2 tolerance, (b) no increase in ABA content was observed in CdCl2-treated leaves of TN1 rice seedlings, which are sensitive to CdCl2, (c) pretreatment of TN1 rice seedlings with ABA resulted in an enhancement of Cd tolerance, and (d) inhibitor of ABA synthesis, fluridone, increased the sensitivity of TNG67 rice seedlings to CdCl2.
CdCl2 treatment resulted in an increase in Cd content in leaves of TN1 rice seedlings, but not in those of TNG67 rice seedlings. The increase in Cd content in leaves of TNG67 rice seedlings is possibly due to the increase by ABA-inhibited transpiration, which reduced the mobilility of Cd from solution or roots to shoot.
The decrease in protein content was faster in leaves of TN1 rice seedlings treated with CdCl2 than those in the absence of CdCl2. Protein degradation might contribute to the decrease in protein content in leaves of TN1 rice seedlings treated with CdCl2. This conclusion is supported by the observations that the content of total amino acids and the activity of protease are higher in leaves of rice seedlings in the presence of CdCl2 than in those in the absence of CdCl2.
The current results suggest that NH4+ accumulation is associated with the toxicity of leaves of TN1 rice seedlings induced by CdCl2. Evidence was presented to show that CdCl2-induced NH4+ accumulation in leaves of TN1 rice seedlings is attribuited to a decrease in GS activity and Cd per se might directly affect GS activity.
|
|---|
