Abstract
ABSTRACTBeneficial bacteria living in the rhizosphere pose several implications on plant growth promotion and are highly desirable for sustainable agriculture. In the current study, we explored the ameliorative capacity of Leifsonia xyli SE134, a plant growth-promoting rhizobacteria (PGPR), against copper (Cu) stress on tomato grown under elevated Cu levels of 50 and 100 mM. Initially, L. xyli SE134 modulated innate gibberellins (GAs) and indole-3-acetic acid (IAA) metabolism in response to elevated Cu toxicity. The IAA contents increased, whereas that of bioactive GAs decreased in relation to Cu concentration gradient in the broth media. Furthermore, exposure to elevated Cu caused detrimental effects on the physiological attributes as revealed by attenuated shoot length, root length, stem diameter, shoot dry weight, root dry weight, and chlorophyll content in non-inoculated tomatoes as compared to L. xyli SE134 inoculated plants. The growth rescuing effect of L. xyli SE134 may be attributed to the modulation of endogenous amino acids contents in plants, such as glutamic acid, threonine, phenylalanine, glycine, proline, and arginine. Moreover, L. xyli SE134 inoculation stimulated total polyphenol and flavonoid content, reduced super oxide dismutase activity, strongly inhibited Cu, and increased phosphorus and iron content in plants grown under elevated Cu stress. In the absence of Cu toxicity, L. xyli SE134 significantly enhanced amino acid content, improved total flavonoids, and increased phosphorus content, thus resulting in higher plant growth.
Highlights
Unwanted anthropogenic activities have caused significant increases of copper (Cu) levels in agricultural soil beyond the permitted level
The current results demonstrated the unique feature of L. xyli SE134 during copper stress by reprograming its plant growth-promoting characteristics in the form of lowering GA and increasing indole-3-acetic acid (IAA) production (Figure 1)
There is a lack of literature on this subject, and to the best of our knowledge, this is the first report concerning the effects of heavy metal stress on GA metabolism in plant growth-promoting rhizobacteria (PGPR)
Summary
Unwanted anthropogenic activities have caused significant increases of copper (Cu) levels in agricultural soil beyond the permitted level This has masked its beneficial status and importance for the proper functioning of photosynthesis, respiration, enzymes, and proteins in crop plants (Mostofa et al 2015). Other important aspects of PGPR are their phytohormone (gibberellins [GAs], auxins, and ethylene) production ability and their positive effects on plant growth promotion (Khan et al 2016). In auxin groups, indole-3-acetic acid (IAA) is responsible for cell division, elongation, differentiation, root initiation, regulation of gene expression, and ROS homeostasis under abiotic stress conditions to enhance the growth and development process of the plant (Siddiqui et al 2017)
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