| Zinc (Zn) is an important essential micronutrient and its deficiency is a widespread major micronutrient malnutrition problem for human being in the world. Zinc biofortification through staple food crop is regarded as an effective way to solve this problem. Rice is the most important food crop in the world feeding over half of the global population; therefore, slightly increase of zinc contents in rice grain can greatly keep human being out of the problem of zinc deficiency. However, the physiological mechanism of zinc nutrition in Zn-dense rice is not fully understood, which would affect the advance of high Zn-dense rice breeding. In this study, the characteristics of zinc xylem loading in the dense rice, zinc distribution in the whole rice and the micro distribution were studied. The main results were summarized as followings:1. Through hydroponic experiments, the differences in energy demand when xylem loading zinc in both zinc dense and indense rice were determined. Metabolic inhibitors and low temperature greatly inhibited xylem loading zinc in both rice genotypes, and the inhabitation was greater in dense genotype than in indense genotype, which indicated the zinc dense rice is more reliable to metabolic energy when xylem loads zinc..2. After one week zinc deficiency treatments, comparing to control, the xylem loading zinc ability in both zinc dense and indense genotype rices were greatly enhanced. Zinc deficiency raised the zinc concentration from 17.0μM to 32.5μM in the indense IR64 xylem sap; while the increase of from 26.8μM to 37.8μM occurred in zinc dense IR68144. Although the increased rates in IR64 were lower than the one in IR68144, the zinc concentrations and the total zinc amounts in xylem sap were always higher in IR68144 than in IR64 in all treatments. These results suggested zinc dense rice IR68144 has a much higher xylem loading capacity.3. The effects of other ions on the xylem loading zinc capacity were also determined. Iron deficiency greatly enhanced xylem loading zinc capacity in both genotypes. However, La3+, which is known as the calcium channel inhibitor, greatly reduced zinc concentrations in the xylem sap of dense rice, the decrease could also be accomplished by high Ca2+level treatment. However, both La3+ and high Ca2+ level treatment had obvious influence to zinc indense rice. It may induce that the zinc dense rice may uptake zinc ions through the calcium channel while the indense IR64 do not have such functions.4. In hydroponic experiments, additions of organic acid to culture solutions can make little influence to the xylem loading zinc in both genotypes, implying organic acid may facilitate zinc absorption and transportation in rice just in zinc deficient soil or when soil zinc availability is at low level.5. When treated with different zinc level, both Zn-dense and Zn-indense rice's zinc distribution were determined. In filling stage, the stem, old leaf and flag leaf of the rice are the source of zinc while the spike was the sink. When treated with zinc deficiency, the rate of decrees zinc concentration in the flag leaf and old leaf of Zn-dense rice are larger than the Zn-indense one, at the same time, the rate of decrees zinc concentration of rachis, shell and brown rice are less than the Zn-indense one. The zinc concentration of flag leaf of Zn-dense rice was lower than the Zn-indense one when treated with low zinc, but the zinc concentration of flag leaf of Zn-dense rice was much higher than the Zn-indense one in other treatments. So the efficient of transport zinc from flag leaf and old leaf to spike and keep high zinc concentration in spike may be very important for Zn-dense rice.6. When determined the zinc and iron concentration in the seeds of both zinc efficiency and inefficiency rice, zinc concentration in different pars of the seeds of both rice were similar, the correlation of the two elements was high in both kinds rice seed. The accumulation of both zinc and iron was similar and there may have same mechanism in zinc and iron transporting to rice seed. 7. The determination of different parts of the seed showed that the zinc concentration in brown rice and whole seed of zinc efficiency rice were lower than the zinc inefficiency one's. The zinc efficiency rice can uptake zinc efficiently from the soil only when zinc deficiency. But when treated with enough zinc, the zinc efficiency rice can not transport zinc efficiently to the seed. A lot of works are needed to breed zinc efficiency and zinc dense in seed rice. |
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