dase therefore behaves as a typical peroxidase, btit apparently is liniked to an aerobic system which produces H202 as a resuilt of the reactioni of free radical intermediates with 02 (23). Fuirther evideence for the peroxidase natuire of the enzyme was obtainied by Sttutz (21), who failed to separate IAA oxi(dase from peroxidase in preparationis from L'ptri1s by means of starch block electrophoresis.In attempts to correlate changes in IAA oxidlase activity in diseased tobacco tissuies (19) with the acctumtllation of phenolic inhibitors, it was nloted that the enzyme system from tobacco roots followved tuntustual kinetics. Highly active preparations did not exhibit the indtuction period typical of IAA oxidase from other souirces (17). It was felt that these resuilts couild be due to the simuiltanieouis action of IAA oxidase and a separate peroxi(lase in the system. It was also noted that fresh extracts from tobacco roots contained both IAA oxidase and peroxidase activities, but the ability to oxidize IAA disappearedl after the preparations were lyophilized or stored at -100 for several weeks, whereas the activity on polyphenols remained unaffected. The thermal inactivation points and the pH optima for both oxidations were different. \Vhereas these observations were not inconsistent with the view that a single enzyme with 2 separate centers for suibstrate attachment was involved, it seemed more 1200 www.plantphysiol.org on May 9, 2018 -Published by Downloaded from
1987. Detection of heavy metals in oak mycorrhizae of northeastern Pennsylvania forests, using x-ray microanalysis. Can. J. Bot. 65: 2622-2627. A survey of red and white oak mycorrhizae, using semi-quantitative x-ray microanalysis, has shown a significant difference in heavy-metal deposition between the forest-grown oaks on acidic (mor) and neutral (mull) soils. There are significantly higher levels of nickel, iron, aluminum, and copper within oak roots of Pocono (mor) forests than of Lehigh Valley (mull) forests. The Pocono oak roots were taken from acidic soils derived from sandstone, shales, and conglomerate parent rock materials, while Lehigh Valley oak roots were removed from neutral soils derived from carbonate-rich limestone and dolomite. Chemical analysis of these soils demonstrated higher plant-available heavy-metal content in the acidic soils. Digital line profiles indicated that heavy metals, especially nickel and iron, were concentrated in the peripheral mycorrhizal mantle region of cross-sectioned roots. Since nickel and other heavy metals are known to be toxic to fungi and plant tissues, the high concentrations of metals may be responsible for the decreased frequencies of advantageous ectomycorrhizal associations in oaks growing under certain acid-stressed conditions. WASSERMAN, J. L., MINEO, L., MAJUMDAR, S. K., et VAN TYNE, C. 1987. Detection of heavy metals in oak mycorrhizae of northeastern Pennsylvania forests, using x-ray microanalysis. Can. J. Bot. 65 : 2622-2627. A I'aide d'une mCthode semi-quantitative de microanalyse aux rayons-X, les auteurs ont observe, chez les mycorhizes des chknes rouge et blanc, une difference significative dans la dCposition de mCtaux lourds selon que les chknes ont poussC sur des sols acides (mor) ou neutres (mull). On retrouve significativement plus de nickel, de fer, d'aluminium et de cuivre chez les chknes blancs provenant des forkts de Pocono (mor) que ceux provenant des for& de Lehigh Valley (mull). Les racines de chgne venant de Pocono ont Ct C prelevCes sur des sols acides dCrivCs d'une roche-mkre comportant du grks, des schistes et du conglomCrat alors que les racines de chkne venant de Lehigh Valley ont Ct C prClevCes sur des sols neutres dCrivCs d'une rochemkre contenant de la pierre-i-chaux riche en carbonates et de la dolomie. A I'analyse chimique, ces sols acides rtvklent des teneurs plus ClevCes en mCtaux lourds accessibles aux plantes. Les profils d'analyse digitale montrent une plus grande accunlulatin des mCtaux lourds, particulikrement le nickel et le fer, dans la region pCriphCrique du manteau des mycorhizes observCes en coupes transversales. Puisqu'on connait I'effet toxique du nickel et des autres mCtaux lourds sur les champignons et les tissus vCgCtaux, il se pourrait que ces fortes concentrations et les tissus vCgCtaux, il se pourrait que ces fortes concentrations en mCtaux soient responsables pour la diminution de frkquence des associations ectomycorhiziennes avantageuses chez les chknes poussant dans certains sols acides.[Traduit par la ...
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