Role of Zinc–Lysine on Growth and Chromium Uptake in Rice Plants under Cr Stress

Abstract

Chromium (Cr) is a very toxic heavy metal present in agricultural soils. Soils contaminated with Cr are the major source of Cr entrance into the food chain. The present experiment was designed to determine the effects of different levels of lysine chelated with zinc (Zn–lys) (0, 10, 20, 30 mg L−1) upon photosynthesis, biomass, anti-oxidant enzyme activities, oxidative stress, and the uptake of Cr by rice under various applied levels of Cr (0, 100, 500 mg kg−1). Cr stress decreased the physiological and morphological parameters as well as the activities of anti-oxidants enzymes; and caused oxidative stress by enhancing the Cr concentration in plants over that of controls. Zn–lys foliar treatment enhanced photosynthesis, biomass, Zn contents, and enzyme activities. The application of Zn–lys (30 mg L−1) under 500 mg kg−1 of Cr increased plant height by 50% and shoot dry weight by 74% but also the root dry weight by 129% over the control treatment. In addition, Zn–lys reduced oxidative stress and Cr concentration compared to that of Cr treatments alone. The application of Zn–lys (30 mg L−1) also reduced Cr contents in roots by 26 and 31% in 100 and 500 mg kg−1 Cr treatments, respectively. The results of our study revealed that Zn–lys foliar treatment enhanced rice growth and decreased oxidative stress and Cr concentration by stimulating the anti-oxidant defense system as well as by promoting photosynthesis and Zn uptake in rice plants. Overall, the Zn–lys foliar treatment was helpful in increasing plant growth and Zn concentration while reducing the Cr contents in rice. However, further studies at field levels are required to explore the mechanisms of Zn–lys mediated reduction of Cr and possibly other heavy metal toxicity in plants.