Rice adaptation to excess manganese: nutrient accumulation and implications of the quality of crops.

摘要

The nature of the adaptation of rice (Oryza sativa cv. Safari) to Mn toxicity was characterized during late reproductive development. Plants were grown over a 170-day period in nutrient solutions containing 0.5, 2 and 32 mg Mn/litre. It was found that root and shoot growth was significantly inhibited in the highest Mn treatment. Up to the last treatment, the concentrations of Mn also increased significantly in both root and shoot tissues, but the activity of the root ATPase proton pump decreased. In both root and shoot tissues, the release of electrolytes followed a similar pattern to that of Mn accumulation. Additionally, increasing Mn concentrations triggered a general synergistic effect on Ca, Mg, Na, P, Cu and Fe net uptake, but displayed an antagonistic action on K and Zn. The net translocation rate of Fe was also inhibited. Increasing Mn concentrations delayed crop production and altered nutrient accumulation. However, the concentration of potentially toxic metals in the grain was much lower than that in vegetative plant tissues. The concentrations of Ca, K, Na, P and Zn interacted with increasing Mn concentrations mostly in a manner similar to that of the shoot, but a different pattern was found for Mg, Cu and Fe. In these crops, increasing concentrations of Mn did not affect the contents of starch, soluble sugars and oils, but significantly decreased the concentration of protein. Moreover, the amino acid composition showed a significant increase in the concentration of tyramine, but sharply decreased levels of all of the basic amino acids positively charged at physiological pH values. The effects of increasing Mn concentrations on nutrient net uptake and translocation were related to effects on crop production. It was concluded that atthe end of reproductive growth, the adaptation of the cv. Safari to excess Mn is associated with a selective uptake that is likely to decrease crop production and grain protein quality.