Tkalec Mirta, Malarić Kresimir, Pevalek-Kozlina Branka
Department of Botany, Division of Biology, Faculty of Science, University of Zagreb, Rooseveltov trg 6, HR-10000 Zagreb, Croatia.
Sci Total Environ. 2007 Dec 15;388(1-3):78-89. doi: 10.1016/j.scitotenv.2007.07.052. Epub 2007 Sep 7.
Widespread use of radiofrequency radiation emitting devices increased the exposure to electromagnetic fields (EMFs) from 300 MHz to 300 GHz. Various biological effects of exposure to these fields have been documented so far, but very little work has been carried out on plants. The aim of the present work was to investigate the physiological responses of the plant Lemna minor after exposure to radiofrequency EMFs, and in particular, to clarify the possible role of oxidative stress in the observed effects. Duckweed was exposed for 2 h to EMFs of 400 and 900 MHz at field strengths of 10, 23, 41 and 120 V m(-1). The effect of a longer exposure time (4 h) and modulation was also investigated. After exposure, parameters of oxidative stress, such as lipid peroxidation, H(2)O(2) content, activities and isoenzyme pattern of antioxidative enzymes as well as HSP70 expression were evaluated. At 400 MHz, lipid peroxidation and H(2)O(2) content were significantly enhanced in duckweed exposed to EMFs of 23 and 120 V m(-1) while other exposure treatments did not have an effect. Compared to the controls, the activities of antioxidative enzymes showed different behaviour: catalase (CAT) activity increased after most exposure treatments while pyrogallol (PPX) and ascorbate peroxidase (APX) activities were not changed. Exceptions were reduced PPX and APX activity after longer exposure at 23 V m(-1) and increased PPX activity after exposures at 10 and 120 V m(-1). By contrast, at 900 MHz almost all exposure treatments significantly increased level of lipid peroxidation and H(2)O(2) content but mostly decreased PPX activity and did not affect CAT activity. Exceptions were exposures to a modulated field and to the field of 120 V m(-1) which increased PPX and CAT activity. At this frequency APX activity was significantly decreased after exposure at 10 V m(-1) and longer exposure at 23 V m(-1) but it increased after a shorter exposure at 23 V m(-1). At both frequencies no differences in isoenzyme patterns of antioxidative enzymes or HSP70 level were found between control and exposed plants. Our results showed that non-thermal exposure to investigated radiofrequency fields induced oxidative stress in duckweed as well as unspecific stress responses, especially of antioxidative enzymes. However, the observed effects markedly depended on the field frequencies applied as well as on other exposure parameters (strength, modulation and exposure time). Enhanced lipid peroxidation and H(2)O(2) content accompanied by diminished antioxidative enzymes activity caused by exposure to investigated EMFs, especially at 900 MHz, indicate that oxidative stress could partly be due to changed activities of antioxidative enzymes.
发射射频辐射设备的广泛使用增加了对300兆赫至300吉赫电磁场（EMF）的暴露。到目前为止，已记录了暴露于这些场的各种生物学效应，但针对植物的相关研究很少。本研究的目的是调查浮萍（Lemna minor）暴露于射频电磁场后其生理反应，特别是阐明氧化应激在观察到的效应中可能发挥的作用。浮萍在10、23、41和120 V m⁻¹的场强下暴露于400和900兆赫的电磁场中2小时。还研究了更长暴露时间（4小时）和调制的影响。暴露后，评估氧化应激参数，如脂质过氧化、H₂O₂含量、抗氧化酶的活性和同工酶模式以及HSP70表达。在400兆赫时，暴露于23和120 V m⁻¹电磁场的浮萍中脂质过氧化和H₂O₂含量显著增加，而其他暴露处理没有影响。与对照组相比，抗氧化酶的活性表现出不同的行为：大多数暴露处理后过氧化氢酶（CAT）活性增加，而邻苯三酚（PPX）和抗坏血酸过氧化物酶（APX）活性没有变化。例外情况是在23 V m⁻¹下长时间暴露后PPX和APX活性降低，以及在10和120 V m⁻¹下暴露后PPX活性增加。相比之下，在900兆赫时，几乎所有暴露处理都显著增加了脂质过氧化水平和H₂O₂含量，但大多降低了PPX活性，且不影响CAT活性。例外情况是暴露于调制场和120 V m⁻¹的场中，PPX和CAT活性增加。在此频率下，在10 V m⁻¹下暴露以及在23 V m⁻¹下长时间暴露后APX活性显著降低，但在23 V m⁻¹下短时间暴露后增加。在两个频率下，对照植物和暴露植物之间抗氧化酶的同工酶模式或HSP70水平均未发现差异。我们的结果表明，对所研究的射频场进行非热暴露会在浮萍中诱导氧化应激以及非特异性应激反应，尤其是抗氧化酶的反应。然而，观察到的效应明显取决于所施加的场频率以及其他暴露参数（强度、调制和暴露时间）。暴露于所研究的电磁场，特别是在900兆赫时，导致脂质过氧化和H₂O₂含量增加，同时抗氧化酶活性降低，这表明氧化应激可能部分归因于抗氧化酶活性的改变。
