Abstract
Plant growth promoting rhizobacteria (PGPR) with 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity has the potential to promote plant growth and development under adverse environmental conditions. In the present study, rhizobacterial strains were isolated from Garlic (Allium sativum) rhizosphere and were screened in vitro ACC deaminase activity in DF salt minimal media supplemented with 3 mM ACC. Out of six isolates, two could degrade ACC into α-ketobutyrate, exhibiting ACC deaminase activity producing more than ∼1500 nmol of α-ketobutyrate mg protein-1 h-1, and assessed for other plant growth promoting (PGP) functions including indole acetic acid production (greater than ∼30 μg/ml), siderophore, Ammonia, Hydrogen cyanide production and inorganic Ca3(PO4)2 (∼85 mg/L) and ZnSO4 solubilization. Besides facilitating multifarious PGP activities, these two isolates augmented in vitro stress tolerance in response to 6% w/v NaCl salt stress and drought stress (-0.73 Mpa). The strains ACC02 and ACC06 were identified Aneurinibacillus aneurinilyticus and Paenibacillus sp., respectively on the basis of 16S rDNA gene sequence analysis and were evaluated for growth promoting potential in French bean seedlings under non-saline and salinity stress conditions through pot experiments. The seed bacterization by ACC02 and ACC06 revealed that treatment of plants with bacterial isolates in the form of consortia significantly declined (∼60%) stress stimulated ethylene levels and its associated growth inhibition by virtue of their ACC deaminase activity. The consortia treatment alleviated the negative effects of salinity stress and increased root length (110%), root fresh weight (∼45%), shoot length (60%), shoot fresh weight (255%), root biomass (220%), shoot biomass (425%), and total chlorophyll content (∼57%) of French bean seedlings subjected to salinity stress.
Highlights
In most of the developing countries, the crop production is majorly hampered by the negative impact of abiotic and biotic stress
A total of twenty rhizobacteria were isolated from rhizospheric soil of A. sativum on enrichment media, of which, six strains were able to grow on DF minimal salt medium supplemented with 3 mM ACC as a nitrogen source, implying ACC deaminase activity
The highest ACC deaminase activity was exhibited by bacterial strain ACC02 (1677 nmol α-ketobutyrate mg protein−1 h−1) followed by ACC06 (1589 nmol α-ketobutyrate mg protein−1 h−1), ACC11 (936 nmol α-ketobutyrate mg protein−1 h−1), ACC04 (916 nmol α-ketobutyrate mg protein−1 h−1), ACC12 (891 nmol α-ketobutyrate mg protein−1 h−1) and ACC07 (824 nmol α-ketobutyrate mg protein−1 h−1) (Figure 1A).The highest enzymatic activity of ACC deaminase produced by ACC02 and ACC06, i.e., conversion of nitrogen source ACC into α-ketobutyrate, was further verified by Fourier-transform infrared spectroscopy (FTIR) spectra analysis results (Figure 2), which showed peaks at 1689 and 3343 cm−1, confirming the presence of a ketonic group and amino functional group, respectively recognized as α-ketobutyrate as per Sarkar et al (2018)
Summary
In most of the developing countries, the crop production is majorly hampered by the negative impact of abiotic (environmental stressors) and biotic stress. Ethylene is a plant hormone involved in regulation of various physiological processes of plants, but the climate change induced ethylene production in plants inflicts a significant reduction in plant growth and development and if not monitored properly could result in plant death (Iqbal et al, 2017; Dubois et al, 2018). Excessive presence of salts in soil (soil salinity) is one of the major problematic factors responsible for a reduction of plant growth and crop productivity across the globe. High concentration of salt (NaCl) enhanced the stress ethylene production and induced ion toxicity, oxidative stress, and disturbed the osmotic potential in plants. The problem of soil salinity is frequent in arid and semiarid regions, aggravating due to irrational use of chemical fertilizers and improper use of irrigation water (Bharti et al, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
