Use of Tradescantia clone 4430 for direct long-term soil mutagenicity studies

Abstract

Soil mutagens permanently and directly affect terrestrial plants, soil microorganisms and invertebrates and indirectly impact vertebrate and human populations. However, the dynamic response to soil mutagens under conditions of long-term exposure has been studied insufficiently. The clonal nature of Tradescantia #4430 and the well-developed associated test systems for evaluation of genotoxicity allow investigation of the permanent effects of direct exposure to the soil not only on plants of the same genotype, but even with the same individual plants, as was done in the present study. Twenty soil samples of different origin were studied in Tradescantia after 0.5, 1 and 2 years of direct exposure to the soil, in order to examine the induction of pink cells (PC), colorless cells (CC) and branched hairs (BH). Additionally, after 0.5 years, micronucleus (MN) formation was assessed, and after 1 year, the variation of random amplified polymorphic DNA (RAPD) markers was evaluated. Nine soil samples were of urban origin, and the others came from different soils from former military grounds. The results of the 0.5-year exposure were compared with the effects of aqueous/DMSO extracts tested in previous work. The long-term exposure period allowed not only a better differentiation of the soils within territories, but also permitted detection of differences between soils of urban and military origin. The results also depended on the test used to evaluate genotoxicity. The 'burst' phenomenon, consisting of a sudden increase of BH variation and, especially, of CC, was observed only in tests of samples from several military sites, mainly after a 2-year exposure. MN formation was less frequent after 0.5 years of exposure compared with the results from aqueous extracts, and this difference was highly significant. The variation of the RAPD markers in a significant portion of the soil samples coincided with a higher level of variation according to other tests (PC, CC, BH), but predicting the genotoxicity of the soils based on their elemental soil composition at the end of the experiment was impossible. At several points where a 'burst' was observed, the concentration of a number of elements was lower. A cumulative effect is hypothesized to explain these observations. Tradescantia clone #4430 is the most suitable system for such studies.

Keywords: Burst effects; DNA-RAPD test; Direct exposure; Long-term dynamics; Soil genotoxicity; Tradescantia tests.