Impact of lead on the amount of chlorophyll and carotenoids in the leaves of Triticum durum and T. aestivum, Hordeum vulgare and Avena sativa

H. Souahi

doi:10.15421/012125

Abstract

Lead is one of the most dangerous pollutants to both the environment and humans. It causes structural changes in photosynthetic apparatus and reduced biosynthesis of chlorophyll pigments inhibits carbon metabolism. The aim of our study was to determine the dynamics of photosynthetic pigments in leaves of wheat (Triticum durum and T. aestivum), barley (Hordeum vulgare) and oats (Avena sativa) at different lead acetate, Pb(CH3COO)2 levels: 0, 0.15, 0.30 and 0.60 g/L. The results of this research indicate that these concentrations significantly affected chlorophyll content of H. vulgare and A. sativa as compared to T. durum and T. aestivum. Analysis of variance showed that lead concentration and interaction between cereal species had a significant effect on all chlorophyll characteristics at 0.1% probability and on carotenoids contents at 1% significance. Lead acetate in 0.3 and 0.6 g/L concentrations had a highly significant effect on chlorophyll a, b and carotenoids in H. vulgare seedlings, its carotenoid contents increased from 0.002 mg/g FW at 0 g/L to 0.107 mg/g FW at 0.6 g/L, whereas its chlorophyll content decreased under heavy metal stress, corresponding to the concentration of the metal ion. Carotenoids of A. sativa were not affected compared to Chl a and Chl b, while higher concentrations significantly increased chlorophyll contents of the seedlings from 1.384 mg/g FW of total chlorophyll at 0 g/L to 1.883 mg/g FW at 0.6 g/L. The increased amount of carotenoids was indicative of the formation of free radicals in plants under heavy metal stress, while decreased levels of chlorophyll content were an indication of reduction in the growth of the plants leading to decrease in the yield. It is suggested that chlorophyll content can be adopted as a very useful in vivo indicator of heavy metal toxicity.

Highlights

Heavy metals, for example lead (Pb), occur naturally on the earth’s surface and are released during the weathering process
The most extreme acceptable weekly intake of Pb in human food is about 25 μg/kg of human body weight (Fang et al, 2014). It is available in small amounts in almost all food crops and its concentration is considerably heightened when crops are grown in Pbcontaminated soils
Vascular bundles and total chlorophyll contents, and reduced CO2 influx because of stomatal closure are the vital reasons for the shortened photosynthesis under lead stress (Romanowska et al, 2006)

Summary

Introduction

For example lead (Pb), occur naturally on the earth’s surface and are released during the weathering process. It has been shown that plants exposed to lead ions exhibited a decrease in the photosynthetic rate because of distorted chloroplast, limited synthesis of chlorophyll, blocked electron transport, stopped activities of Calvin cycle enzymes, as well as deficiency of CO2 as a result of stomatal closing (Sharma & Dubey, 2005). It causes accumulation of a large number of ROS, which disrupt the ultrastructure of cellular organelles especially the cell membranes (Shahid et al, 2015). The objective of the research presented here was the dynamics of photosynthetic pigments of crops after the plants’ exposure to Pb(CH3COO)

Materials and methods

Results

Conclusions