Effects of cadmium on metallothionein gene expression and mineral elements uptake in tomato (lycopersicon esculentum)

Abstract

Cadmium is one of the most toxic heavy metal and important environmental pollutants. It is a nonessential element that affects plant growth and development. Plants have evolved different mechanisms to minimize its harmful effects. Metallothioneins (MT) are low molecular weight proteins that bind metal ions. MT genes can be induced by various heavy metals and they are expressed high levels in tissues. The accumulation of Cd in plants may cause several physiological, biochemical and structural changes such as alteration in mineral elements uptake. The goal of the present study is to determine the MT gene expression, Cd accumulation and mineral elements uptake in different tissues of tomato exposed to cadmium. Tomato seedlings were grown in pots under the greenhouse conditions. Total RNA were extracted by using Plant RNA isolation Kit (Biobasic). cDNA synthesis and real time PCR was performed QuantiTect SYBR Green RT-PCR protocols (Qiagen). The contents of Cd and mineral elements in dry matter were quantified using ICP-MS. Cadmium induced MT gene expression in all plant tissues. The induction was seen in all treatment groups and the highest MT response was detected in leaves of tomato. Expression level in ripening fruits was low as compared to roots and leaves. Binding of heavy metals to MTs protects plant from metal stress. The present results indicate that MTs was stimulated by cadmium uptake. Cd content increased in all treatment groups. The highest Cd level was determined in roots, followed by leaves and fruits. Cadmium affected the levels of mineral elements in plant, differently. Unlike the amount of Fe, Ca decreased depending on the increasing of Cd doses in leaves. Mg, Ca, Fe contents increased, whereas Mn content decreased in fruits. Cd show synergistic or antagonistic effects on the mineral accumulation in plant, depending on its amount and type of tissue.