Abstract
Cadmium stress significantly decreases agricultural productivity worldwide. Plant growth-promoting rhizobacteria (PGPR) are eco-friendly and inexpensive tool for mitigating heavy metal stress in crops. We isolated rhizospheric bacteria and screened them for various plant growth-promoting (PGP) traits as well as Cd tolerance. Only 6 bacterial isolates out of 55 assessed showed multiple PGP traits in response to different Cd concentrations. The Bacillus cereus ALT1 strain showed high tolerance to increased Cd amounts in the culture medium, while secreting indole-3-acetic acid (IAA) and organic acids into the culture medium. High Cd concentrations (0.7 mM, 1.4 mM, and 2.1 mM) reduced soybean shoot and root length, root/shoot fresh and dry weight, as well as chlorophyll content; however, inoculation with the bacterial isolate ALT1 mitigated Cd stress and enhanced both soybean growth parameters and chlorophyll content. It also decreased abscisic acid (ABA) amounts, enhanced salicylic acid (SA) production, and promoted antioxidant response by increasing total proteins (TP) and superoxide dismutase (SOD), while decreasing glutathione (GSH) content, lipid peroxidation (LPO), peroxidase (POD), superoxide anion (SOA), and polyphenol oxidase (PPO) in soybean plants. In addition, inductively coupled plasma mass spectrometry (ICP-MS) showed that soybean plants treated with the bacterial isolate ALT1 enhanced K uptake and decreased Cd amounts in comparison to control plants. The present study reveals that Cd-tolerant bacterial isolate ALT1 can alleviate Cd toxicity on plants by increasing their growth, thus imposing itself as an eco-friendly bio-fertilizer under Cd stress.
Highlights
Heavy metals are widespread pollutants in the surface soil layer and represent one of the world’s major environmental problems posing considerable risk to agricultural crops [1].Geological and anthropogenic activities further increase heavy metals’ concentration in soil to the levels that are harmful to both plants and animals [2,3]
Cd belongs to most toxic heavy metals that lead to decrease of crop productivity [2,4]
These results corroborate with the previous findings [41,42], which reported that bacterial genera such as Klebsiella and Serratia, and fungal species Neotyphodium gansuense are able to diminish Cd stress and enhance growth of Solanum nigrum and Achnatherum inebrians
Summary
Heavy metals are widespread pollutants in the surface soil layer and represent one of the world’s major environmental problems posing considerable risk to agricultural crops [1].Geological and anthropogenic activities further increase heavy metals’ concentration in soil to the levels that are harmful to both plants and animals [2,3]. Cd belongs to most toxic heavy metals that lead to decrease of crop productivity [2,4]. Many vegetable crops accumulate Cd in their tissues which can cause severe developmental disruptions [5]. Physiological, biochemical, and phytochemical changes in plants [2]. Morphological and physiological changes are visible through all growth stages such as germination, seedling development, vegetative phase and maturation [6,7,8]. Biochemical and phytochemical change include either inhibition or activation of cytoplasmic enzymes, modulation of phytohormones, photosynthesis pigment depletion, and cell structure damaging due to accumulation of reactive oxygen species [9,10]. K is involved in protein and amino acids’ synthesis, as well as in photosynthesis of plants growing under either normal or stressful conditions [12]
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