Abstract
Maize seedlings grown in a nutrient solution were treated with Cd (50, 100 µM) or Cu (50, 100 µM). Roots and separated leaf sections (from the youngest––basal, through the middle––mature, to the oldest––apical) were analysed. Shoot and root fresh weight, and root net growth rates were reduced significantly after Cu application in comparison to Cd. Copper (50, 100 µM) and cadmium (100 µM) decreased the sum of chlorophyll and total carotenoid pools mostly in mature and old leaf sections. The concentration of Cu and Cd increased in the old and mature leaf sections. Analysis of organic acids showed that both metals differently influenced the low-molecular-weight organic acids (LMWOAs) content in maize leaf sections. In mature sections, the excess Cu increased the succinate and tartrate contents, whereas in the young ones mainly the tartrate level was elevated. Cadmium elevated citrate accumulation in mature and old sections, compared to the control plants. Malate, the main LMWOA in maize leaves, increased only after addition of 100 µM of Cd (mature and old sections) or 50 µM of Cu (old sections). Analysis of LMWOAs in roots showed that the excess of Cd or Cu induced higher accumulation of tartrate and malate and, additionally, copper increased the citrate content.
Highlights
Some of the heavy metals (HMs) such as iron, zinc, or copper are essential for normal growth, their presence at excess concentrations in soil becomes toxic to plants
Analysis of organic acids showed that both metals differently influenced the lowmolecular-weight organic acids (LMWOAs) content in maize leaf sections
For MDA determination, 0.5 g of each plant leaf section or roots was homogenised in 0.1 % trichloroacetic acid (TCA) and centrifuged at 10,0009g for 10 min. 0.5 % 2-thiobarbituric acid (TBA) in 20 % TCA was added to the supernatant
Summary
Some of the heavy metals (HMs) such as iron, zinc, or copper are essential for normal growth, their presence at excess concentrations in soil becomes toxic to plants These trace elements as well as non-essential HMs. Acta Physiol Plant (2014) 36:1565–1575 such as lead or cadmium induce several mechanisms of plant adaptation to HMs stress. On the other hand, when HMs enter the cytosol, intercellular mechanisms are involved in detoxification thereof In such a situation, detoxification of HMs including an efflux of HMs from root cells due to H?coupled antiport activity (Burzynski et al 2005), metal transport, chelation, and sequestration into vacuole was observed (Rauser 1999; Sanitadi Toppi and Gabbrielli 1999). Low-molecular-weight organic acids (LMWOAs) participate in both strategies of HMs detoxification: firstly, as plant exudates, organic acids increase extracellular precipitation of HMs by the chelation oxidation–reduction reaction in the rhizosphere; secondly, likewise phytochelatins (PCs) and amino acids, LMWOAs chelate and sequestrate HMs in the vacuole (Rauser 1999; Ma 2000; Ryan et al 2001)
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