Significance: Although plant growth–promoting bacteria (PGPB) enhance the performance of plants, only a few mechanisms have been identified so far. We show that the sulfur metabolisms in both PGPB Enterobacter sp. SA187 and Arabidopsis plants play a key role in plant salt stress tolerance. Salt stress induces a sulfur starvation response in plants that is attenuated by SA187. Arabidopsis sulfur metabolic mutants are hypersensitive to salt stress but can be rescued by SA187. Most plant sulfur metabolism occurs in chloroplasts and is linked to stress-induced accumulation of reactive oxygen species that is suppressed by SA187. This work reveals that plant salt stress tolerance requires the coordinated regulation of the sulfur metabolic pathways in both beneficial microbe and host plant.

Recently, the use of nanofertilizers has received a great deal of attention in managing plants under biotic and abiotic stresses. However, studies that elucidate the role of silicon dioxide nanoparticles (SiO₂NPs) in regulating maize tolerance to drought stress are still at early stages of development. In this study, plants that were treated with SiO₂NPs (0.25 g/L as foliar spray) displayed considerable improvement in the growth indices, despite being subjected to drought stress. In addition, the action of SiO₂NPs led to a considerable rise in the levels of chlorophylls, proline, cell membrane integrity, leaf water content, and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (G-POX)). In contrast, an inverse trend was seen in the oxidative injury, the total amount of soluble sugars, and the activity of ascorbate peroxidase (APX). At the same time, carotenoids were unaffected in SiO₂NPs-treated and non-treated plants under drought stress. The results of the molecular investigation that was conducted using qRT-PCR showed that the relative expression of the D2 protein of photosystem II (PsbD) was elevated in SiO₂NPs-treated plants in response to drought stress, while the expression of the osmotic-like protein (OSM-34) and aquaporin (AQPs) was downregulated in SiO₂NPs-treated plants in response to drought stress. This research could pave the way for further investigations into how SiO₂NPs boost plant resistance to drought stress.

The use of beneficial microbes to mitigate drought stress tolerance of plants is of great potential albeit little understood. We show here that a root endophytic desert bacterium, Pseudomonas argentinensis strain SA190, enhances drought stress tolerance in Arabidopsis. Transcriptome and genetic analysis demonstrate that SA190-induced root morphogenesis and gene expression is mediated via the plant abscisic acid (ABA) pathway. Moreover, we demonstrate that SA190 primes the promoters of target genes in an epigenetic ABA-dependent manner. Application of SA190 priming on crops is demonstrated for alfalfa, showing enhanced performance under drought conditions. In summary, a single beneficial root bacterial strain can help plants to resist drought conditions.

Numerous plant metabolites, especially amino acids, are accumulated as a result of stress. These amino acids are crucial for plant metabolism and development and have historically been viewed as the building blocks of proteins. Several studies suggested that there is a link between proline buildup and exposure plants to stress. Proline performs important functions under stress in addition to be a great osmolyte, antioxidant enzyme, acts as an antioxidant defense and signaling molecules. Two field trials were during two successive winter seasons (2020/2021 and 2021/2022). The effects of proline foliar application (0, 100, 200, 300 and 400 mg L−1) and irrigation water levels (irrigation by 100, 80 and 60% of crop water requirements, CWR, CWR100, CWR80 and CWR60, respectively) on plant pigments, antioxidants activity, yield traits and nutrient contents of wheat were assessed. The experiment was designed in a split-plot involving 4 replicates. Drought stress (CWR80 and CWR60) led to reductions in photosynthetic pigments, and yield components. Under severe water stress (CWR60), proline 200 and 300 mg L−1 recorded the highest values of chlorophyll a, chlorophyll b, and total pigments. Application of proline 300 mg L−1 was the potent practice for enhancing the antioxidant activity% (DPPH radical scavenging) and phenols content under CWR100 and CWR80. Indole acetic acid (IAA) possessed the maximum values with proline 200 mg L−1 under all irrigation patterns. Under severe deficit water (CWR60), without proline spraying (for super oxide dismutase), 200, 300 or 400 mg L−1 proline (for peroxidase) and 200 or 400 mg L−1 proline (for polyphenol oxidase) recorded the highest values. Spraying proline 300 mg L−1 achieved the highest values of grain number spike−1, weight of 1000 grains and grain yield ha−1 under different irrigation regimes. In conclusion, proline is considered a good mitigator for drought stress, due to it increased wheat plant tolerance to water deficiency throughout improving plant physiology and consequently yields quantity and quality. The most efficient concentrations of proline for coping the adverse impact of drought were 200 and 300 mg L−1.

This study aimed to evaluate the effects of dietary supplementation with nano-curcumin (NCur) and a nano-curcumin/chitosan blend (NCur/Ch) on growth performance, digestibility, immune response, antioxidant status, intestinal morphometric characters, and gene regulation in Nile tilapia. Fish (n = 180, initial body weight = 12.0 ± 0.53 g) received supplementary NCur at rates of 0 (control), 0.00625, and 0.0125, and NCur/Ch at rates of 0.00625 + 0.5 g/kg diet for 4 weeks. Growth performance parameters (final weight and length, body mass gain, specific growth, and length gain rates) were markedly increased, and the feed conversion ratio was significantly decreased in the NCur- and NCur/Ch-supplemented groups. Digestive enzyme (amylase), immune response markers (immunoglobulin M, nitrous oxide, and lysozyme activity), plasma albumin, and total protein were increased significantly, mainly with a diet supplemented with 0.00625 g NCur/kg. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), glucose, and cortisol levels decreased in the supplemented groups compared to the control. Significantly increased glutathione peroxidase (GPx) and decreased malondialdehyde (MDA) levels were observed in the NCur/Ch group. Superoxide dismutase (SOD) activity was improved in the 0.0125 NCur group. Intestinal morphometric characters, including villus length, width, interspace, and goblet cell abundance, were increased to cope with improved growth performance and were associated with upregulation of insulin-like growth factor 1 (igf-1) and complement C-5 (cc5) compared to the control group. Therefore, NCur and an NCur/Ch blend could be supplemented in the Nile tilapia diets as a natural alternative to promote growth, digestion, immune status, liver function, antioxidant status, and related gene expression in O. niloticus.