Expression analysis of metallothioneins and mineral contents in tomato (Lycopersicon esculentum) under heavy metal stress

Abstract

Heavy metals are considered to be the most important pollutants in the contamination of soils; they adversely affect plant growth and development and cause some physiological and molecular changes. The contamination of agriculturalsoils by heavy metals has changed the mineral element content of vegetables. Plant metallothioneins (MTs) are thought to have the functional role in heavy metal homeostasis, and they are used as the biomarkers for evaluating environmental pollution. We aimed to evaluate the expression of MT isoforms (MT1, 2, 3 and 4) and some mineral element composition of tomato roots, leaves and fruits exposed to copper and lead. RESULTS: Heavy metal applications increased MT1 and MT2 gene expressions compared to the control in the tissues of tomato. The highest level of MT1 and MT2 transcripts was found in roots and leaves, respectively. The expression of MT3 is induced in roots, leaves and fruits except for Pb treatment in roots. MT4 expression increased in fruits; however, other tissues did not show a clear change. Our results indicated that Cu content was higher than Pb in all tissues of tomato. The lower doses of Cu (10 ppm) increased the content of Mg, Fe, Ca and Mn in roots. Pb generally increased the level of minerals in leaves and fruits, but it decreased Mg, Mn and Fe contents in roots. CONCLUSION: Both heavy metals not only moved to aerial parts but also caused alterations to mineral element levels. These results show that MT transcripts are regulated by Cu and Pb, and expression pattern changes to MT isoforms and tissue types