A Chemically Induced New Pea (Pisum sativum) Mutant SGECdt with Increased Tolerance to, and Accumulation of, Cadmium
1 All-Russia Research Institute for Agricultural Microbiology, Podbelskogo 3, Pushkin 8, 196608, St Petersburg, Russian Federation
2 Department of Biochemistry and Physiology of Plants W5, Bielefeld University, University Str. 25, 33501, Bielefeld, Germany
* For correspondence. E-mail belimov{at}rambler.ru
Received: 27 July 2006 Returned for revision: 12 September 2006 Accepted: 18 October 2006
BACKGROUND AND AIMS: To date, there are no crop mutants described in the literature that display both Cd accumulation and tolerance. In the present study a unique pea (Pisum sativum) mutant SGECdt with increased Cd tolerance and accumulation was isolated and characterized.
METHODS: Ethylmethane sulfonate mutagenesis of the pea line SGE was used to obtain the mutant. Screening for Cd-tolerant seedlings in the M2 generation was performed using hydroponics in the presence of 6 µM CdCl2. Hybridological analysis was used to identify the inheritance of the mutant phenotype. Several physiological and biochemical characteristics of SGECdt were studied in hydroponic experiments in the presence of 3 µM CdCl2, and elemental analysis was conducted.
KEY RESULTS: The mutant SGECdt was characterized as having a monogenic inheritance and a recessive phenotype. It showed increased Cd concentrations in roots and shoots but no obvious morphological defects, demonstrating its capability to cope well with increased Cd levels in its tissues. The enhanced Cd accumulation in the mutant was accompanied by maintenance of homeostasis of shoot Ca, Mg, Zn and Mn contents, and root Ca and Mg contents. Through the application of La+3 and the exclusion of Ca from the nutrient solution, maintenance of nutrient homeostasis in Cd-stressed SGECdt was shown to contribute to the increased Cd tolerance. Control plants of the mutant (i.e. no Cd treatment) had elevated concentrations of glutathione (GSH) in the roots. Through measurements of chitinase and guaiacol-dependent peroxidase activities, as well as proline and non-protein thiol (NPT) levels, it was shown that there were lower levels of Cd stress both in roots and shoots of SGECdt. Accumulation of phytochelatins [(PCcalculated) = (NPT)–(GSH)] could be excluded as a cause of the increased Cd tolerance in the mutant.
CONCLUSIONS: The SGECdt mutant represents a novel and unique model to study adaptation of plants to toxic heavy metal concentrations.
Key words: Cadmium tolerance, calcium, glutathione, heavy metals, nutrient homeostasis, pea mutant, Pisum sativum
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