Physiology And Modelling Of Zinc Uptake Partitioning And Accumulation In Aerobic Rice

With fresh water shortage becoming a serious global issue, aerobic rice {Oryza sativa) is becoming one of the main food resources for human being, and the nutritional quality especially like micronutrient (Fe, Zn and others) content of aerobic rice is also highly valued. However, the mechanism of the uptake, accumulation and partitioning of zinc by aerobic rice is poorly documented both at home and abroad. The present research focused on the zinc partitioning and accumulation in individual organ and the genetic variation in grain zinc mass fraction under greenhouse pot and field culture condition, and some process of zinc partitioning in plant was quantified and simulated, the results were as follows:1. Significant variance existing between accessions in grain zinc mass fraction in aerobic rice. Under the same culture condition, the content of the highest grain zinc mass fraction was about doubled compared with that of the lowest accession. Under lower zinc condition, the range of grain zinc mass fraction among the test accessions under pot culture and field condition was 27.26~47.17 mg kg-1, 8.96—18.32 mg kg-1 respectively; and 28.86~57.53 mg kg-1 , 16.45—29.60 mg kg-1 under sufficient zinc supply. Combined with higher grain zinc mass fraction and partitioning ratio of zinc to the grain, 89B271-17Hun, Handao9 , Handao 297 under low zinc supply condition and Handao 297, 90B10-1 under sufficient zinc supplied level are defined as high zinc-accumulation cultivars and optimal cultivars. Significant correlationship was found between grain zinc mass fraction and zinc partitioning ratio to the grain (zinc harvest index), and also between zinc harvest index and harvest index. Whereas, under excessive zinc supply, luxury zinc was kept by vegetative organ not grain. So it should be possible to develop high grain zinc mass fraction plants through either traditional plant breeding methods or molecular biological techniques to alleviate Zn deficiency in human populations.2. Zinc mass fraction in grain was correlated with shoot zinc mass fraction, when the shoot zinc mass fraction was below 100 mg kg-1, with increasing zinc supply, grain zinc mass fraction increased with higher shoot zinc mass fraction; however, when shoot zinc mass fraction was above100 mg kg-1, grain zinc mass fraction still increased but slowly, with most zinc detained in non-grain parts of the plants. The results indicated that grain zinc mass fraction could only be increased 2 to 3 times to its most. Based on the correlationship between shoot zinc mass fraction and grain zinc mass fraction, the relationship between zinc source and sink could be divided into three categories: zinc-sink restricted type, zinc source-sink coordinated type, and zinc source restricted type. Zinc source restricted type was among the most common. This rang true especially under field condition when the shoot zinc mass fraction was often under 100 mg kg ', which was far from sufficient for grains; When the shoot zinc mass fraction was above 100 mg kg ', the plants contain far more zinc than grains necessary need, and this was called zinc source restricted type; When the shootzinc mass fraction was 30 to 100 mg kg1, it was named zinc-sink coordinated type.3. The uptake of zinc was unrestricted, while the zinc accumulation in grain was controlled. With increasing zinc supply, plant could keep taking up zinc although the zinc content might be above optimal demand, or even toxicity level, and the extra zinc was found to mainly store in sheath. Zn harvest index (ZNHI) was increased with Zn supply increasing , but when Zn mass fraction in shoot was high (40 kg. mg), zinc harvest index was sharply decreased with increasing zinc level, like in solution culture experiment (from above 0.2 to about 0.02). The observation demonstrated that the uptake of zinc of the plant was unrestricted, while the zinc accumulation in grain was controlled, that there might possibly exist an effective defending mechanism during the zinc transfer to grains.4. It was insufficient zinc source in the...