Effects of plant growth-promoting rhizobacteria strains producing ACC deaminase on photosynthesis, isoprene emission, ethylene formation and growth of Mucuna pruriens (L.) DC. in response to water deficit.
Agricultural sustainability is an increasing need considering the challenges posed by climate change and rapid human population growth. The use of plant growth-promoting rhizobacteria (PGPR) may represent an excellent, new agriculture practice to improve soil quality while promoting growth and yield of important crop species subjected to water stress conditions. In this study, two PGPR strains with 1-Aminocyclopropane-1-Carboxylate (ACC) deaminase activity were co-inoculated in velvet bean plants to verify the physiological, biochemical and molecular responses to progressive water stress. The results of our study show that the total biomass and the water use efficiency of inoculated plants were higher than uninoculated plants at the end of the water stress period. These positive effects may be derived from a lower root ACC content (-45 %) in water-stressed inoculated plants than in uninoculated ones resulting in lower root ethylene emission. Furthermore, the ability of inoculated plants to maintain higher levels of both isoprene emission, a priming compound that may help to protect leaves from oxidative damage, and carbon assimilation during water stress progression may indicate the underlining metabolic processes conferring water stress tolerance. Overall, the experimental results show that co-inoculation with ACC deaminase PGPR positively affects tolerance to water deficit, confirming the potential for biotechnological applications in water-stressed agricultural areas.
Brunetti C
，Saleem AR
，Della Rocca G
，Emiliani G
，De Carlo A
，Balestrini R
，Khalid A
，Mahmood T
，Centritto M
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Diversity analysis of ACC deaminase producing bacteria associated with rhizosphere of coconut tree (Cocos nucifera L.) grown in Lakshadweep islands of India and their ability to promote plant growth under saline conditions.
ACC deaminase producing Plant growth promoting rhizobacteria (PGPR) offers a great promise for ameliorating the negative impacts of salinity stress manifested on plants. In this context, 28 rhizospheric bacteria associated with ACC deaminase potential (198-1069 nmol α-ketobutyrate mg protein-1 h-1) were isolated from 5 different islands of Lakshadweep, union territory, India- Agatti, Kavaratti, Bangaram, Kadmat, and Thinnakara islands using DF-minimal medium. The diversity of cultivable ACC deaminase producing bacteria was analysed by PCR-RFLP (Restriction Fragment Length Polymorphism) method using three endonucleases AluI, MspI and HaeIII which led to the grouping of these isolates into six clusters at 80 % similarity index. Subsequently, isolates were functionally characterized for various PGP traits such that indole-3-acetic acid (IAA) production (∼10-80 μg mL-1); 16 isolates had phosphate solubilizing potential ranging from ∼19 to 88 P mg L-1 ; siderophore and ammonia production abilities were observed in 5 and 24 isolates, respectively while two strains tolerated up to 8% NaCl. Phylogenetic analysis of 16S rRNA gene sequences of representative strain from each cluster revealed that twenty-eight ACC deaminase producing PGPR belong to eight distinct genera: Pseudomonas, Bacillus, Azospirillum, Azotobacter, Escherichia, Paenibacillus, Burkholderia, and Klebsiella. Two isolates, CO1 (Pseudomonas putida) and CO8 (Bacillus paramycoides) were evaluated for plant growth promoting effects on French bean (Phaseolus vulgaris) under salinity (100 mM NaCl) stress. Both the selected isolates in consortium form significantly increased the root length, shoot length, root fresh and dry weight, shoot fresh and dry weight of French bean seedlings exposed to salinity stress, compared to non-inoculated control plants. The co-inoculation with selected strains CO1 and CO8 has significantly improved chlorophyll concentration, relative water content, membrane stability index, gas exchange parameters including net photosynthesis rate (PN), stomatal conductance (gs), transpiration rate (E) and water use efficiency of French bean plants by ∼100 %, ∼85 %, ∼40 %, ∼198 %, ∼80 %, ∼70 % and ∼75 %, respectively under saline conditions in comparison with non-inoculated plants. Moreover, the consortium treated French bean plants showed lower levels of stress-induced ethylene by 38 %, electrolyte leakage and Malondialdehyde (MDA) content by ∼15 % under salt stress compared to non-inoculated ones. This study unveiled the potential of halotolerant strains, Pseudomonas putida and Bacillus paramycoides as French bean biofertilizers in mitigating the adverse effects of salinity in plant growth in sustainable agriculture.
Pandey S
，Gupta S
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1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase-containing rhizobacteria protect Ocimum sanctum plants during waterlogging stress via reduced ethylene generation.
Ocimum sanctum grown as rain-fed crop, is known to be poorly adapted to waterlogged conditions. Many a times the crop suffers extreme damages because of anoxia and excessive ethylene generation due to waterlogging conditions present under heavy rain. The usefulness of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-containing plant growth promoting rhizobacteria was investigated under waterlogging stress. The comparison of herb yield and stress induced biochemical changes of waterlogged and non-waterlogged plants with and without ACC deaminase-containing microbiological treatments were monitored in this study. Ten plant growth promoting rhizobacteria strains containing ACC-deaminase were isolated and characterized. Four selected isolates Fd2 (Achromobacter xylosoxidans), Bac5 (Serratia ureilytica), Oci9 (Herbaspirillum seropedicae) and Oci13 (Ochrobactrum rhizosphaerae) had the potential to protect Ocimum plants from flood induced damage under waterlogged glass house conditions. Pot experiments were conducted to evaluate the potential of these ACC deaminase-containing selected strains for reducing the yield losses caused by waterlogging conditions. Bacterial treatments protected plants from waterlogging induced detrimental changes like stress ethylene production, reduced chlorophyll concentration, higher lipid peroxidation, proline concentration and reduced foliar nutrient uptake. Fd2 (A. xylosoxidans) induced maximum waterlogging tolerance as treated waterlogged plants recorded maximum growth and herb yield (46.5% higher than uninoculated waterlogged plants) with minimum stress ethylene levels (53% lower ACC concentration as compared to waterlogged plants without bacterial inoculation) whereas under normal non-waterlogged conditions O. rhizosphaerae was most effective in plant growth promotion.
Barnawal D
，Bharti N
，Maji D
，Chanotiya CS
，Kalra A
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