Exophiala sp. LHL08 reprograms Cucumis sativus to higher growth under abiotic stresses

Endophytic fungi are potential sources of secondary metabolites; however, they are little known for phytohormones secretion and amelioration of plant growth under abiotic stresses. We isolated a novel endophyte from the roots of Cucumis sativus and identified it as a strain of Exophiala sp. by sequencing internal transcribed spacer/large subunit rDNA and phylogenetic analysis. Prior to identification, culture filtrate (CF) of Exophiala sp. has shown significant growth promotion of Waito‐C [a gibberellins (GAs)‐deficient mutant cultivar] and Dongjin‐byeo (normal GAs biosynthesis cultivar) rice seedlings. CF analysis of Exophiala sp. showed the presence of physiologically active GAs (GA₁, GA₃, GA₄ and GA₇) and inactive GAs (GA₅, GA₈, GA₉, GA₁₂ and GA₂₀). Exophiala sp. had higher GAs in its CF than wild‐type strain of Gibberella fujikuroi except GA₃. Influence of Exophiala sp. was assessed on cucumber plant's growth and endogenous abscisic acid (ABA), salicylic acid (SA) and bioactive GAs under salinity and drought stresses. Exophiala sp.‐treated plants have shown significantly higher growth and rescued the host plants from stress promulgated water deficit, osmotic and cellular damage. The altered levels of stress‐responsive ABA showed low level of stress confined to endophyte‐applied plants than control. Elevated levels of SA and bioactive GAs (GA₃ and GA₄) in endophyte‐associated plants suggest stress‐modulating response toward salinity and drought. In conclusion, symbiotic relations between Exophiala and cucumber have reprogrammed the host plant growth under abiotic stresses, thus indicating a possible threshold role of endophytic fungi in stress alleviation. This study could be extended for improving agricultural productivity under extreme environmental conditions.     

Bacterial endophyte Sphingomonas sp. LK11 produces gibberellins and IAA and promotes tomato plant growth

Plant growth promoting endophytic bacteria have been identified as potential growth regulators of crops. Endophytic bacterium, Sphingomonas sp. LK11, was isolated from the leaves of Tephrosia apollinea. The pure culture of Sphingomonas sp. LK11 was subjected to advance chromatographic and spectroscopic techniques to extract and isolate gibberellins (GAs). Deuterated standards of [17, 17-²H₂]-GA₄, [17, 17-²H₂]-GA₉ and [17, 17-²H₂]-GA₂₀ were used to quantify the bacterial GAs. The analysis of the culture broth of Sphingomonas sp. LK11 revealed the existence of physiologically active gibberellins (GA₄: 2.97 ± 0.11 ng/ml) and inactive GA₉ (0.98 ± 0.15 ng/ml) and GA₂₀ (2.41 ± 0.23). The endophyte also produced indole acetic acid (11.23 ± 0.93 μM/ml). Tomato plants inoculated with endophytic Sphingomonas sp. LK11 showed significantly increased growth attributes (shoot length, chlorophyll contents, shoot, and root dry weights) compared to the control. This indicated that such phyto-hormones-producing strains could help in increasing crop growth.     

Endophytic fungal pre-treatments of seeds alleviates salinity stress effects in soybean plants

In the present study, four endophytic fungi (GM-1, GM-2, GM-3, and GM-4) were tested for their ability to improve soybean plant growth under salinity stress conditions. The seed germination and plant growth were higher in seeds pretreated with endophytic fungal cultures than their controls. The positive influence of fungi on plant growth was supported by gibberellins analysis of culture filtrate (CF), which showed wide diversity and various concentrations of GAs. Specifically, GA₄, GA₇, GA₈, GA₉, GA₁₂, and GA₂₀ were found in fungal CFs. Under salinity stress conditions, GM-1 significantly enhanced the length and fresh weight of soybean plants relative to other fungal treatments. GM-1 effectively mitigated the adverse effects of salinity by limiting lipid peroxidation and accumulating protein content. GM-2, GM-3, and GM-4 also counteracted the salinity induced oxidative stress in soybean plants through reduction of lipid peroxidation and enhancement of protein content, maintaining the length and fresh weight of shoots. The activities of the antioxidant enzymes catalase, superoxide dismutase and peroxidase were inhibited in salinity exposed plants, while GM-1 significantly enhanced these antioxidant enzyme activities in plants under salt stress. GM-1 treatment also showed lower levels of abscisic acid and elevated levels of salicylic acid in plants under salinity stress. Hence, GM-1 was identified as Fusarium verticillioides (teleomorph Gibberella moniliformis) isolate RK01 based on its DNA sequence homology. These results suggest that endophytic fungal (F. verticillioides) pre-treatment of soybean seeds would be an effective method to promote soybean plant growth under salinity stress conditions.     

Salinity stress resistance offered by endophytic fungal interaction between Penicillium minioluteum LHL09 and glycine max. L

Endophytic fungi are little known for their role in gibberellins (GAs) synthesis and abiotic stress resistance in crop plants. We isolated 10 endophytes from the roots of field-grown soybean and screened their culture filtrates (CF) on the GAs biosynthesis mutant rice line - Waito-C. CF bioassay showed that endophyte GMH-1B significantly promoted the growth of Waito-C compared with controls. GMH-1B was identified as Penicillium minioluteum LHL09 on the basis of ITS regions rDNA sequence homology and phylogenetic analyses. GC/MS-SIM analysis of CF of P. minioluteum revealed the presence of bioactive GA(4) and GA(7). In endophyte-soybean plant interaction, P. minioluteum association significantly promoted growth characteristics (shoot length, shoot fresh and dry biomasses, chlorophyll content, and leaf area) and nitrogen assimilation, with and without sodium chloride (NaCl)-induced salinity (70 and 140 mM) stress, as compared with control. Field-emission scanning electron microcopy showed active colonization of endophyte with host plants before and after stress treatments. In response to salinity stress, low endogenous abscisic acid and high salicylic acid accumulation in endophyte-associated plants elucidated the stress mitigation by P. minioluteum. The endophytic fungal symbiosis of P. minioluteum also increased the daidzein and genistein contents in the soybean as compared with control plants, under salt stress. Thus, P. minioluteum ameliorated the adverse effects of abiotic salinity stress and rescued soybean plant growth by influencing biosynthesis of the plant's hormones and flavonoids.     

Endophytic bacteria (Sphingomonas sp. LK11) and gibberellin can improve Solanum lycopersicum growth and oxidative stress under salinity

This study aims to understand the effects of salinity on the growth and oxidative stress enzymes of endophytic bacteria (Sphingomonas sp. LK11) and tomato plants. In response to salinity and gibberellic acid (GA₄), catalase (CAT), superoxide dismutase, and reduced glutathione were significantly regulated in LK11 as compared to peroxidase (POD) and polyphenol oxidase (PPO). Salinity stress to tomato plants caused significant cessation in growth and biomass, which was accompanied by threefold increase in lipid peroxidation and decrease in glutathione, CAT, POD, and PPO activities. In contrast, sole and combined treatment of LK11 and GA₄ rescued plant growth and biomass production whilst exhibited lower lipid peroxidation and higher glutathione content under salinity stress. The activities of CAT, POD, and PPO were either lower or nonsignificant as compared to control. In conclusion, inoculation of bacterial endophytes offers a relative stress counteracting potentials as evidenced by the known plant growth regulators.     

Plant growth promoting effect of <Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> H-2-5 on crop plants and influence on physiological changes in soybean under soil salinity

This study was aimed to identify plant growth-promoting bacterial isolates from soil samples and to investigate their ability to improve plant growth and salt tolerance by analysing phytohormones production and phosphate solubilisation. Among the four tested bacterial isolates (I-2-1, H-1-4, H-2-3, and H-2-5), H-2-5 was able to enhance the growth of Chinese cabbage, radish, tomato, and mustard plants. The isolated bacterium H-2-5 was identified as Bacillus amyloliquefaciens H-2-5 based on 16S rDNA sequence and phylogenetic analysis. The secretion of gibberellins (GA₄, GA₈, GA₉, GA₁₉, and GA₂₀) from B. amyloliquefaciens H-2-5 and their phosphate solubilisation ability may contribute to enhance plant growth. In addition, the H-2-5-mediated mitigation of short term salt stress was tested on soybean plants that were affected by sodium chloride. Abscisic acid (ABA) produced by the H-2-5 bacterium suppressed the NaCl-induced stress effects in soybean by enhancing plant growth and GA₄ content, and by lowering the concentration of ABA, salicylic acid, jasmonic acid, and proline. These results suggest that GAs, ABA production, and the phosphate solubilisation capacity of B. amyloliquefaciens H-2-5 are important stimulators that promote plant growth through their interaction and also to improve plant growth by physiological changes in soybean at saline soil.     

Phytohormones Related to Host Plant Manipulation by a Gall-Inducing Leafhopper

The maize orange leafhopper Cicadulina bipunctata (Hemiptera: Cicadellidae) induces galls characterized by growth stunting and severe swelling of leaf veins on various plants of Poaceae. Previous studies revealed that galls are induced not on feeding site but on distant, newly extended leaves during the feeding, and strongly suggested that some chemicals injected by the leafhopper affect at the leaf primordia. To approach the mechanism underlying gall induction by C. bipunctata, we examined physiological response of plants to feeding by the leafhopper. We performed high-throughput and comprehensive plant hormone analyses using LC-ESI-MS/MS. Galled maize leaves contained higher contents of abscisic acid (ABA) and trans-Zeatin (tZ) and lower contents of gibberellins (GA₁ and GA₄) than ungalled maize leaves. Leafhopper treatment significantly increased ABA and tZ contents and decreased GA₁ and GA₄ contents in extending leaves. After the removal of leafhoppers, contents of tZ and gibberellins in extending leaves soon became similar to the control values. ABA content was gradually decreased after the removal of leafhoppers. Such hormonal changes were not observed in leafhopper treatment on leaves of resistant maize variety. Water contents of galled leaves were significantly lower than control leaves, suggesting water stress of galled leaves and possible reason of the increase in ABA content. These results imply that ABA, tZ, and gibberellins are related to gall induction by the leafhopper on susceptible variety of maize.     

Gibberellin-producing Promicromonospora sp. SE188 improves Solanum lycopersicum plant growth and influences endogenous plant hormones

Plant growth-promoting rhizobacteria (PGPR) producing gibberellins (GAs) can be beneficial to plant growth and development. In the present study, we isolated and screened a new strain of Promicromonospora sp., SE188, isolated from soil. Promicromonospora sp. SE188 secreted GAs into its growth medium and exhibited phosphate solubilization potential. The PGPR produced physiologically active (GA₁ and GA₄) and inactive (GA₉, GA₁₂, GA₁₉, GA₂₀, GA₂₄, GA₃₄, and GA₅₃) GAs in various quantities detected by GC/MS-SIM. Solanum lycopersicum (tomato) plants inoculated with Promicromonospora sp. SE188 showed a significantly higher shoot length and biomass as compared to controls where PGPR-free nutrient broth (NB) and distilled water (DW) were applied to plants. The presence of Promicromonospora sp. SE188 significantly up-regulated the non C-13 hydroxylation GA biosynthesis pathway (GA₁₂→GA₂₄→GA₉→GA₄→ GA₃₄) in the tomato plants as compared to the NB and DW control plants. Abscisic acid, a plant stress hormone, was significantly down-regulated in the presence of Promicromonospora sp. SE188. Contrarily, salicylic acid was significantly higher in the tomato plant after Promicromonospora sp. SE188 inoculation as compared to the controls. Promicromonospora sp. SE188 showed promising stimulation of tomato plant growth. From the results it appears that Promicromonospora sp. SE188 has potential as a bio-fertilizer and should be more broadly tested in field trials for higher crop production in eco-friendly farming systems.     

Endophytes Aspergillus caespitosus LK12 and Phoma sp. LK13 of Moringa peregrina produce gibberellins and improve rice plant growth

Two new strains of endophytic fungi were isolated from the bark of Moringa peregrina and identified as Aspergillus caespitosus LK12 and Phoma sp. LK13. These endophytes were identified through amplifying polymerase chain reaction (PCR) and sequencing the 18S internal transcribed spacer of DNA extracted from both endophytes. Pure cultures of endophytic fungi were subjected to extract and isolate gibberellins (GAs). Deuterated standards of [17,17-²H₂]-GA₁, [17,17-²H₂]-GA₃, [17, 17-²H₂]-GA₄ and [17, 17-²H₂]-GA₇ were used to quantify the endophytic fungal GAs. The analysis revealed that both the endophytes are producing bioactive GAs in various quantities (ng mL^?1). A. caespitosus LK12 was producing GA₁ (54.51 ± 1.23), GA₄ (26.5 ± 0.65), and GA₇ (2.87 ± 1.23) while Phoma sp. LK13 was secreting GA₁ (4.8 ± 0.12), GA₃ (8.65 ± 0.21), GA₄ (23.7 ± 0.98), and GA₇ (22.7 ± 0.73). The culture filtrate (CF) of A. caespitosus and Phoma sp. significantly increased the shoot length of GAs-deficient mutant waito-c and normal Dongjin-beyo rice seedlings as compared to control. Application of such growth-promoting and GAs-producing endophytes can ameliorate poorly growing crop plants.     

Gibberellins and Abscisic Acid Promote Carbon Allocation in Roots and Berries of Grapevines

Carbon allocation within grapevines may affect berry growth and development. The plant hormones gibberellins (GAs) and abscisic acid (ABA) control various processes across the plant life and both have been involved in assimilate production and transport in different species. Hence, this work examined the distribution of sugars (sucrose, fructose, and glucose) and starch in grapevines at veraison after foliar applications of GA₃, ABA, and an inhibitor of GA biosynthesis, paclobutrazol (PBZ). The results demonstrated that GA₃ increased total grapevine mass, with carbon allocated to the whole grapevine (as structural and soluble carbohydrates). Both GA₃ and ABA increased monosaccharide (glucose and fructose) levels in berries (up to tenfold) and roots (up to threefold). However, GA₃ increased the net carbon fixation whereas ABA did not. PBZ diminished most growth parameters except grapevine mass, and allocated more carbohydrates to roots (up to threefold more sucrose and starch). Such results indicate that GAs promote net carbon fixation and transport, whereas ABA as a stress signal only enhances sugar transport; notwithstanding the two hormones promoted carbon allocation toward roots and berries.