|MadSci Network: General Biology|
According to the reference(1), concentration of total Zn in root of wheat seedling's cytoplasm can be 0.4mM (i.e. about 25mg/L). However, based on a widely used recipe of plant growing medium -- Murashige and Skoog salt(2), Zn concentration at 0.03 mM (1.95mg/L of Zn2+) will be enough for many kinds of plants. I am not sure what plant your are testing and what the environment you are applying on the plant, both would influence your experimental result. But generally speaking, plant in 0.1mg/l solution would probably show one or several Zn deficiency symptoms, like: young leaves growth reduction; leaf margin distorted or puckered; light sensitive and interveinel choloroses in leaves; retardation of stem growth(3). However I did not find reference about the effects of excessive Zn for plant, probably because in nature, the problem for plants is deficiency of Zn rather than excess of it. I would like to know your experimental results, especially the one about 100mg/L Zn. About the function of Zn, you are right, it is mainly about enzyme. Zn, which is absorbed as divalent form, is important for more than 80 enzyme's function. Although I can not tell you the names of all these enzymes, most of the critical function of Zn in cells is related to its ability to form tetrahedral coordination bonds in different cell development stages. For example, some amino acids can form tetrahedral coordination bonds with Zn rather than with Fe, thus prevents Fe induced production of highly toxic hydroxyl radicals. Also, over-oxidation will result as toxic resource to cells, especially for electron-transport reactions which are critical part for photosynthesis and respiration; Zn might be involved in the expression of some enzymes which can decrease oxidative level, thus protect cell from oxidative damages. In addition, animal studies showed that Zn is involved in restriction of programmed cell death. All the above demonstrated that Zn is important for plant growth and development. Reference: (1) Cakmak I.Tansley Review No.111- Possible roles of zinc in protecting cells from damage by reactive oxygen species. New Pgytologist. 146(2):185- 205, 2000 May (2) Murashige, T and Skoog, F.(1962) Physiol. Plant.15,485 (3)Frank B Salisbury and Cleon W.Ross. Plant Phyiology. (1992) Wadsworth Publish Co.ISBN 0-534-15162-0 Chapter 6.
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