Application of Plant Growth-Promoting Bacteria as an Eco-Friendly Strategy for Mitigating the Harmful Effects of Abiotic Stress on Plants

Abstract

Plant growth-promoting bacteria (PGPB) play an important role in improving agricultural production under several abiotic stress factors. PGPB can be used to increase crop growth and development through hormonal balance and increase nutrient uptake. The positive effect of PGPB may be due to its pivotal role in morphophysiological and biochemical characteristics like leaf number, leaf area, and stem length. Furthermore, relative water content, chlorophyll content, carotenoids, antioxidant enzymes, and plant hormones were improved with PGPB treatment. Crop yield and yield components were also increased with PGPB treatment in numerous crops. The anatomical structure of plant organs was increased such as lamina thickness, stem diameter, xylem vessel diameter, and number of xylem vessels as well as phloem thickness under treatment with PGPB. Additionally, PGPB can alleviate the negative effects of several abiotic stresses by regulating the antioxidant defense system to scavenge the reactive oxygen species resulting in an improvement of yield production in the stressed plants. Additionally, gene expres-sions were controlled by calcium ion modulation during secondary messengers that act upon calcium-dependent protein kinase and protein phosphatases. This includes many transcription factors such as MYB, AP2/ERF, bZIP, and NAC which regulate genes related to salinity stress signals. PGPB can demonstrate induction genes of signaling under abiotic stress conditions. This review gives an outline of the PGPB role in alleviating the harmful effects of abiotic factors such as salinity, drought, and heat associated with the improvement of the morpho-physiological and biochemical features especially, leaves and branches number, leaf area, antioxidant compounds, plant hor-mones, and relative water content.