Our study aimed to evaluate intraspecific variability of pea ( L.) in Al tolerance and to reveal mechanisms underlying genotypic differences in this trait. At the first stage, 106 pea genotypes were screened for Al tolerance using root re-elongation assay based on staining with eriochrome cyanine R. The root re-elongation zone varied from 0.5 mm to 14 mm and relationships between Al tolerance and provenance or phenotypic traits of genotypes were found. Tolerance index (TI), calculated as a biomass ratio of Al-treated and non-treated contrasting genotypes grown in hydroponics for 10 days, varied from 30% to 92% for roots and from 38% to 90% for shoots. TI did not correlate with root or shoot Al content, but correlated positively with increasing pH and negatively with residual Al concentration in nutrient solution in the end of experiments. Root exudation of organic acid anions (mostly acetate, citrate, lactate, pyroglutamate, pyruvate and succinate) significantly increased in several Al-treated genotypes, but did not correlate with TI. Al-treatment decreased Ca, Co, Cu, K, Mg, Mn, Mo, Ni, S and Zn contents in roots and/or shoots, whereas contents of several elements (P, B, Fe and Mo in roots and B and Fe in shoots) increased, suggesting that Al toxicity induced substantial disturbances in uptake and translocation of nutrients. Nutritional disturbances were more pronounced in Al sensitive genotypes. In conclusion, pea has a high intraspecific variability in Al tolerance and this trait is associated with provenance and phenotypic properties of plants. Transformation of Al to unavailable (insoluble) forms in the root zone and the ability to maintain nutrient uptake are considered to be important mechanisms of Al tolerance in this plant species.

A b s t r a c tCrops vary considerably in their resistance to acidic soils, and many legumes, including pea (Pisum sativum L.), considered to be sensitive or moderately sensitive crops compared to cereals. The main factor determining the phytotoxicity of acidic soils is the increased concentration of mobile aluminum ions in the soil solution. Accumulation of aluminum in root tissues interferes with cell division, initiation of growth of lateral roots and uptake of minerals and water by plants. Under laboratory conditions the resistance of plants to aluminum is estimated by the degree of damage to the roots by aluminum using dyes (hematoxylin, eriochrome cyanine R) and the ability of roots to restore growth after toxic effect of this metal. This work dedicated to the development of rapid assessment of aluminum tolerance especially for peas, which is as follows: the seeds were germinated in the growth chamber in the nutrient solution for 3 days (7000 lx illumination, temperature of 19 С at night and 21 С during the day, photoperiod 16 h), treated with a toxic concentration of aluminum chloride (3 mg Al/l) for 24 hours, incubated in fresh nutrient solution without aluminum for 2 days and stained with 0.1 % eriochrome cyanine R for 10 min. Zone of root tissue damage by aluminum painted in the color purple. Plant resistance to aluminum was determined by the length of the root re-growth area after exposure to the toxicant. Using 19 varieties of pea from the N.I. Vavilov Research Institute of Plant Industry collection (VIR collection) it was shown that pea has high variability in tolerance to aluminum. Varieties with a minimum (1.01.5 mm) length of the root re-growth (k-2759, k-3654 and k-3283) were characterized by intense purple color of the root, but varieties with a maximum (14.014.5 mm) length of the root re-growth (k-4376, k-9504 and k-7307) had a faint but detectable staining. The proposed method makes it possible to identify genotypes contrasting in aluminum tolerance, is highly reproducible and can be used for screening and study of intraspecific variability in this trait of pea plants at very early developing stage.

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