Uptake Of Outer Source Iodine By Vegetables And Chemical Species Analysis Of Iodine

Iodine is one of the necessary trace elements to human bodies. It plays an so important part in the forming of thyroid hormone that it has great significance to human nutrition. It has been well known that iodine deficiency can result in goiter , and this has become an global sanitation problem. It's reported that the highest bioavailability of iodine by human can amount to 99%, so it will be very meaningful to increase the content of iodine in food. But inorganic iodine can't be well absorbed by bodies and even produces toxicity. Iodine will have wide edible valuation only when it is transformed into biological active organic iodine.In our studies, a hydroponic experiment was carried out to investigate the influence of iodine species(iodide, iodate and iodoacetic Acid) and levels on iodine uptake by vegetables as well as on the growth and quality of vegetables. Besides, radioactive iodine (¹²⁵I) was chosen to basically discuss the chemical species of iodine in leafy vegetables (total iodine,water soluble iodine,organic iodine,I^-,I0₃^-). The objectives of the studies are to provide theoretic basic for studying iodine uptake and accumulation by vegetables and chemical species analysis of iodine in vegetables, and ultimately afford effective,safe and scientific approach to the prevention and cure of iodine deficiency disorders (IDD).The main conclusions we reached through our studies are as follows:(1)Nutrient solution added iodine can distinctly enhance the biomass of both leafy vegetables and fruity vegetables within the proper range of iodine levels, however, high iodine levels can inhibit the growth of vegetables. Therefore, excessive iodine levels should be avoided so as to increase the biomass and to take up adequate iodine by vegetables. Furthermore, except Ipomoea aquatica Forsk, the tolerance of Bok-choy,eggplant and hot pepper to three species of iondine is : CH₂IC00^->I0₃^->I^-, which indicates that compared with inorganic iodine, organic iodine has less toxicity to vegetables.(2)Nutrient solution added different iodine species and levels can obviously enhance the indine content in vegetables, and within the proper range of iodine levels, the iodine content in different part of vegetables enhances with the increase of iodine levels. (3)Vegetables take up iodine mainly through roots. In our studies, the iodine content in roots of Bok-choy,eggplant and hot pepper is much higher than in the other parts of those vegetables (the proportion of iodine content in roots to in other parts is more than 2 to 1), especially the iodine content in fruit of eggplant and hot pepper is even smaller. In the process of transporting iodine from roots to shoots, most of the iodine reserved in the leaf because of the active interception of leaf, and accordingly only very small amount of iodine is transported to the fruit, which shows that the content of iodine transported to shoots especially to the edible parts from roots is limited.(4)The capacity of iodine-enrichment varies in different species of vegetables. The capacity of iodine-enrichment of vegetables is: Ipomoea aquatica Forsk> Bok-choy > eggplant > hotpepper, that is, leafy vegetables > fruity vegetables. What's more, concentration coefficient of low iodine levels is higher than that of high iodine levels. Thereby, leafy vegetables can be chosen as iodine-enrichment vegetables when treated with proper iodine levels.(5)Iodine uptake by vegetables is different in iodine species. The respective effects of iodine uptake by leafy vegetables and fruity vegetables are: CH₂ICOO^->IO₃^->I^-, I^->CH₂ICOO^->IO₃^-.(6)As a whole, nutrient solution added proper range of I^-levels can enhance the content of Vc and decrease the content of nitrate in leafy vegetables; treated with I0₃^- can decrease the content of Vc and increase the content of nitrate; while treated with CH₂IC00^- can both decrease the content of Vc and nitrate.(7)The results of study on ¹²⁵I indicate that chemical species and contents of iodine in Bok-choy and Ipomoea aquatica Forsk are remarkably different. Water soluble iodine maily consists of I^- in both Bok-choy and Ipomoea raquatica Forsk, and respectively with 66. 72% and 57.08% of total water soluble iodine being I^-. Iodine combined with protein is the main form of organic iodine, which respectively amounts to 22. 43% and 3. 68% of total iodine.