Growth-Promoting Effect of Rhizobacterium (Bacillus subtilis IB22) in Salt-Stressed Barley Depends on Abscisic Acid Accumulation in the Roots

Abstract

An ABA-deficient barley mutant (Az34) and its parental cultivar (Steptoe) were compared. Plants of salt-stressed Az34 (100 mmol m−3 NaCl for 10 days) grown in sand were 40% smaller than those of “Steptoe”, exhibited a lower leaf relative water content and lower ABA concentrations. Rhizosphere inoculation with IB22 increased plant growth of both genotypes. IB22 inoculation raised ABA in roots of salt-stressed plants by supplying ABA exogenously and by up-regulating ABA synthesis gene HvNCED2 and down-regulating ABA catabolic gene HvCYP707A1. Inoculation partially compensated for the inherent ABA deficiency of the mutant. Transcript abundance of HvNCED2 and related HvNCED1 in the absence of inoculation was 10 times higher in roots than in shoots of both mutant and parent, indicating that ABA was mainly synthesized in roots. Under salt stress, accumulation of ABA in the roots of bacteria-treated plants was accompanied by a decline in shoot ABA suggesting bacterial inhibition of ABA transport from roots to shoots. ABA accumulation in the roots of bacteria-treated Az34 was accompanied by increased leaf hydration, the probable outcome of increased root hydraulic conductance. Thereby, we tested the hypothesis that the ability of rhizobacterium (Bacillus subtilis IB22) to modify responses of plants to salt stress depends on abscisic acid (ABA) accumulating in roots.

The effects of multiwalled carbon nanotubes and Bacillus subtilis treatments on the salt tolerance of maize seedlings

“…In the present study, the ABA content in the plant leaves decreased after the application of MWCNTs, consistent with the findings from a study by Zhang et al (2017a). Low ABA levels are often maintained in the leaves of B. subtilis-treated plants ( Barnawal et al, 2017;Woo et al, 2020;Akhtyamova et al, 2021). In our study, a significant negative correlation was observed between the ABA content and leaf/root K + content (Figure 4, P < 0.001), and PCA revealed a close relationship between the K + content and ABA content (Figure 3, P < 0.001).…”

Effects of Phytohormone-Producing Rhizobacteria on Casparian Band Formation, Ion Homeostasis and Salt Tolerance of Durum Wheat

“…Using a similar experimental model, we have recently shown that bacterization leads to an increase in the concentration of abscisic acid (ABA) in the roots of salt-stressed plants [ 29 , 44 ]. In those experiments, the highest level of ABA was recorded in plants inoculated with B. subtilis IB-22.…”

“…In those experiments, the highest level of ABA was recorded in plants inoculated with B. subtilis IB-22. Accumulation of ABA in plants treated with B. subtilis IB-22 was shown to be due to upregulation of the ABA synthesis gene HvNCED2 and downregulation of the ABA catabolic gene HvCYP707A1 [ 44 ]. The role of this hormone in the regulation of ion homeostasis in salt-stressed plants is being actively discussed [ 6 , 45 ] and deserves further study.…”

The Effects of Rhizosphere Inoculation with Pseudomonas mandelii on Formation of Apoplast Barriers, HvPIP2 Aquaporins and Hydraulic Conductance of Barley

“…Furthermore, bacteria could increase the root ABA levels by stimulating plant ABA synthesis. Recently, we have shown an increase in the expression level of the NCED gene responsible for ABA synthesis in barley plants treated with Bacillus subtilis IB22 [ 36 ]. Auxins can also up-regulate this rate-limiting gene responsible for ABA synthesis [ 37 ].…”