Date Published: March 13, 2019
Publisher: Public Library of Science
Author(s): Zahra Saeed, Muhammad Naveed, Muhammad Imran, Muhammad Asaad Bashir, Annum Sattar, Adnan Mustafa, Azhar Hussain, Minggang Xu, Ricardo Aroca.
The objective of the study was to evaluate role of zeolite and Enterobacter sp. MN17 on Cd uptake, growth, physiological and biochemical responses of Brassica napus on Cd-contaminated soil. A sandy clay loam soil in plastic pots was spiked with Cd (0 and 80 mg kg-1) and amended with zeolite (0 and 10 g kg-1). Seeds of B. napus were inoculated with Enterobacter sp. MN17. Both inoculated and non-inoculated seeds of B. napus were sown and plants were harvested after 60 days of growth and data were collected. Although sole application of zeolite and seed inoculation reverted adverse effects of Cd in B. napus plants, the combined use resulted in even higher growth and physiological responses compared to control plants. The combined use under Cd stress increased plant height, root length, dry biomass of shoot and root up to 32%, 57%, 42% and 64%, respectively compared to control. The different physiological attributes (photosynthetic rate, chlorophyll content, transpiration rate, stomatal conductance) of B. napus were improved from 6% to 137%. Moreover, combined use of zeolite and seed inoculation on Cd-contaminated soil reduced the stress to plants as antioxidant activities decreased up to 25–64%, however enzyme activities were still higher than plants grown on normal soil. Root and shoot analysis of B. napus for Cd content depicted that zeolite and bacterium decreased Cd uptake from soil. It is concluded that combined use of zeolite and strain MN17 reduces Cd uptake from soil and improves physiological and biochemical responses of B. napus which is helpful to alleviate Cd toxicity to plants.
Heavy metal pollution of water and soil resources is an emergent issue of the modern industrial world. Among heavy metals, cadmium (Cd) is considered as one of the most toxic, non-essential element. It enters into soils through anthropogenic activities, atmospheric deposition, volcanic eruptions and weathering of parent materials [1, 2, 3]. The accumulation of Cd in soil deteriorates its quality, affects soil microbes and interferes uptake of plant essential elements [4, 5, 6], thus seriously limiting crop productivity. Cadmium can cause several morpho-physiological and biochemical disorders in plants . Moreover, food chain contamination with Cd threatens human health [8, 9, 10].
This study evaluates the potential of amending soil with zeolite, an inorganic adsorbent, and seed inoculation with endophytic metal tolerant bacterium, Enterobacter sp. MN17, to mitigate the Cd induced changes in growth, physiology and antioxidant activity of B. napus. Moreover, potential of zeolite and strain MN17 to immobilize Cd in soil with reduced plant uptake has been investigated.
In conclusion, application of zeolite and Enterobacter sp. MN17 significantly enhanced the plant growth, improved physiological and biochemical responses of B. napus in normal and Cd contaminated soils. Moreover, both zeolite amendment and seed inoculation with strain MN17 decreased Cd uptake in root and shoot of B. napus. However, combined application of zeolite and Enterobacter sp. MN17 was found more effective in improving Brassica napus plant height, root length, dry biomass of root and shoot, chlorophyll content, photosynthetic rate, transpiration rate and stomatal conductance in Cd contaminated soil. The antioxidant activity of CAT, APX, SOD, GR, GPX and GST were decreased. Likewise, zeolite and strain MN17 together reduced Cd uptake in root and shoot of B. napus on Cd-contaminated soil.