Wheat Rhizosphere: Effects of ACC deaminase-producing rhizobacteria (Enterobacter cloacae ZNP-4)on wheat growth

A group from Department of Bioengineering and Biotechnology, Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India, etc. has reported about the effects of 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD) producing Plant growth promoting rhizobacterium (PGPR) designated as Enterobacter cloacae ZNP-4 on wheat growth under abiotic stressors such as salt (NaCl) and metal (ZnSO4) stress.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9075627/

Many of the rhizosphere bacteria produce ACCD, which reduces the level of ‘stress ethylene’ in their associated plants by degrading ACC to ammonia and α-ketobutyrate, thereby minimizing the substrate availability for ethylene generation. It has been shown that micro-organisms with ACCD activity >20 nmol α-ketobutyrate mg-1 h-1 are sufficient to enhance plant growth under stress conditions.

Like many other crops, germination of wheat seed and seedling growth are severely affected by salt and metal stress worldwide. The various conventional methods are in practice for alleviating salt stress, but most of them are costly and deleterious to environments. The micro-organisms residing in the rhizosphere have proved to regulate plant growth under normal and stress conditions. Therefore, this study aimed to investigate the effectiveness of ACCD-producing bacterium Enterobacter cloacae ZNP-4 as a biological tool for alleviating the adverse effects of abiotic stressors and examined for its potential to alleviate stress-induced plant growth inhibition.

As a result, the inoculation of strain ZNP-4 significantly improved the various growth parameters of wheat plant such as shoot length (41%), root length (31%), fresh weight (28%), dry weight (29%), photosynthetic pigments chlorophyll a (62%) and chlorophyll b (34%). Additionally, the strain was found to be efficient for minimizing the imposed Zn stress in terms of improving plant growth, biomass and photosynthetic pigments in pots containing different levels of metal stress of 150 mg kg-1 (treatment T1) and 250 mg kg-1 (treatment T2), where (T0: 0 mM; T1: 150 mM, T2: 200 mM NaCl) are different salinity conditions.

In addition, Effect of bacterial inoculation on generation of abiotic stress-induced reactive oxygen species (ROS) was monitored under salinity and metal stress treatments.
The positive effects of PGPR occurred concurrently with the decrease in abiotic stress-induced reactive oxygen species (ROS) molecules such as hydrogen peroxide (H2O2) and superoxide (O2) contents, which lead to lipid peroxidation, membrane deterioration, metabolic and structural dysfunctions, further leading to cell death.
The bacterial inoculation significantly reduced the H2O2 level under tested salinity stress. The highest significant (p=0.05) decrease of 43.2% was recorded at treatment T1 followed by 32.5% at treatment T2. The salinity induced generation of O2 content was also minimized with 52.7% (p=0.05) and 49% (p=0.05) at treatment T1 and T2 in bacterial treated plants.