Differences in photosynthesis, yield and grain cadmium accumulation as affected by exogenous cadmium and glutathione in the two rice genotypes

摘要

Greenhouse pot experiments were conducted using Cd-tolerant (Bing97252) and sensitive (Xiushui63) rice genotypes to investigate genotypic differences in yield, Cd accumulation and photosynthesis at different growth stages in response to different Cd levels and as affected by glutathione (GSH). Yield of the two genotypes were impaired when soil Cd levels higher than 5 mg kg(-1) (Cd2), with Xiushui63 being more affected. Application of GSH at seedling, elongation or the both stages significantly increase yield in Bing97252 and at elongation stage in Xiushui63. Cd concentration in leaves showed dose-dependent responses at seedling and elongation stages except Xiushui63 which showed a slight reduction under Cd5 (100 mg kg(-1)) treatment over Cd4 (50 mg kg(-1)). At harvest stage, leaf Cd concentration also increased with Cd levels in both genotypes. Grain Cd concentration showed dose-dependent increase in Xiushui63, but this increase was only found from control to Cd3 (10 mg kg(-1)) treatments in Bing97252. Addition of GSH markedly decreased grain Cd concentration in both genotypes. Regression equations between grain and leaf Cd concentrations at seedling/elongation stage were established, and the calculated critical levels of Cd in leaves at seedling (0.403 mg kg(-1) DW) and elongation (0.299 mg kg(-1) DW) stages were obtained for safe rice grain production. Net photosynthetic rate and stomatal conductance were not affected at different growth periods under different Cd levels in Bing97252, but significantly reduced at filling stage in Xiushui63 when soil Cd levels up to 50 mg kg(-1). Intercellular CO2 concentration was significantly reduced during the whole growth period under high soil Cd level except seedling stage in Xiushui63, while the decrease was found in Bing97252 only at seedling stage. Our findings demonstrate that adoption of low Cd accumulation genotype coupled with GSH application provided a promising strategy to reduce grain Cd accumulation for safe food production, especially in slight or moderate Cd polluted soils.