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Keywords:

  • cadmium uptake;
  • chlorophyll fluorescence;
  • photosynthesis;
  • stomatal conductance;
  • water-use efficiency

Abstract

Silicon (Si)-induced cadmium (Cd) tolerance in rice (Oryza sativa L.) was investigated by analyzing Cd uptake, growth, and physiological parameters. Silicon treatments (0.0, 0.2, or 0.6 mM) were added to 6 d–old seedlings, and Cd treatments (0.0 or 5.0 μM) were added to 20 d–old seedlings. Parameters determined included: maximum net CO2 assimilation (Amax), stomatal conductance (gsmax), and transpiration (Emax) rates at varying intercellular CO2 concentrations (Ci). Also measured were chlorophyll fluorescence, growth, and Cd-uptake parameters. Results showed a Si-induced inhibition of Cd uptake. However, 0.2 mM or 0.6 mM Si treatment concentrations did not differentially inhibit Cd uptake or differentially alleviate Cd-induced growth inhibition, despite a significant increase in tissue Si concentration due to 0.6 mM Si treatment compared to 0.2 mM Si treatment. Additionally, photosynthesis and chlorophyll-fluorescence analysis showed that treatment with Cd significantly inhibited photosynthetic efficiency. Interestingly, the addition of 0.2 mM Si, more so than the addition of 0.6 mM Si, significantly alleviated the inhibitory effects of Cd toxicity on photosynthesis and chlorophyll-fluorescence parameters. Our results suggest that 0.2 mM Si could be close to an optimum Si-dose requirement for the alleviation of toxicity symptoms mediated by moderate (5 μM) Cd exposure.