Clonal diversity and rare phenes in Taraxacum officinale s.l. coenopopulations from the East-Ural radioactive trace zone

Abstract

The East-Ural radioactive trace (EURT) resulting from an accident at the Mayak Production Association in 1957 is a unique region for estimating the genetic consequences of long-term exposure of natural populations to ionizing radiation. We previously used the example of Taraxacum officinale to demonstrate an increased variation in the viability and radiosensitivity of seed progeny, as well as higher frequencies of abnormal morphogenesis, chromosomal aberrations, and allozyme diversity of plant samples [10, 12]. In this study, we estimated the clonal diversity and qualitative composition of rare morphs in dandelion populations from the EURT zone. The dandelion Taraxacum officinale s.l. is a perennial herbaceous polycarpic plant from the Asteraceae Dumort family. This is an apomictic, triploid ( n = 8), polymorphic species [9]. Within the EURT, two experimental plots located on the central axis of the trail were studied. The impact plot was located in the EURT head (13 km away from the accident center); the buffer plot was located in the middle of the trail (86 km from the center). The background plot was outside the region of radionuclide pollution. Etiolated plant leaves (from at least 70 plants) were used for allozyme analysis in 6.4% polyacrylamide gel in a Tris‐EDTA‐borate system [14]. The gel was stained using the standard technique [13]. The clones, i.e., plant groups with identical multilocal allozyme phenotypes, were distinguished from the allozyme spectra of PGI (two zones of activity), 6-PGDH, FDH, EST, GDH, and GOT. Rare morphs were those represented by one to three plants per sample [3]. Detailed radioecological characteristic of the EURT zone were reported earlier [8, 10]. Note that, taking into account the natural radiation background, additional exposure of meristematic plant tissues on the buffer and impact plots exceeded the background level by factors of 4 and 240, respectively. The community was of the secondary dry herb‐grass meadow type in all plots; the soil of the gray forest type in all plots. In total, 21 clones were identified in all populations studied, most of these clones being unique (figure). In the background and buffer samples, ten and seven allozyme phenotypes were determined, which were represented by 32 (78%) and 82 (87%) plants, respectively. In the impact coenopopulation containing 18 plants (42%), six clones were identified. The only common clone (no. 2) was found in chronically irradiated conopopulations. Although this clone dominated in both plots (53.7 and 27.8% in the middle and head EURT regions, respectively), the proportions of this plant phenotype differed almost twofold in the samples. Coenopopulations of the buffer and background regions also contained a common clone (no. 1), and the corresponding proportions of plants were similar. No common allozyme phenotypes were found in the background and impact coenopopulations. Each population from the EURT zone contained five unique clones,