Plants are subjected to various abiotic stresses, such as drought, extreme temperature, salinity, and heavy metals. Abiotic stresses have negative impact on the physiology and morphology of plants through defects in the genetic regulation of cellular pathways. Plants employ several tolerance mechanisms and pathways to avert the effects of stresses that are triggered whenever alterations in metabolism are encountered. Phytohormones are among the most important growth regulators; they are known for having a prominent impact on plant metabolism, and additionally, they play a vital role in the stimulation of plant defence response mechanisms against stresses. Exogenous phytohormone supplementation has been adopted to improve growth and metabolism under stress conditions. Recent investigations have shown that phytohormones produced by root-associated microbes may prove to be important metabolic engineering targets for inducing host tolerance to abiotic stresses. Phytohormone biosynthetic pathways have been identified using several genetic and biochemical methods, and numerous reviews are currently available on this topic. Here, we review current knowledge on the function of phytohormones involved in the improvement of abiotic stress tolerance and defence response in plants exposed to different stressors. We focus on recent successes in identifying the roles of microbial phytohormones that induce stress tolerance, especially in crop plants. In doing so, this review highlights important plant morpho-physiological traits that can be exploited to identify the positive effects of phytohormones on stress tolerance. This review will therefore be helpful to plant physiologists and agricultural microbiologists in designing strategies and tools for the development of broad spectrum microbial inoculants supporting sustainable crop production under hostile environments.

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Phytohormones and Beneficial Microbes: Essential Components for Plants to Balance Stress and Fitness.

Mechanistic understanding and holistic approach of phytoremediation: A review on application and future prospects

Beneficial features of plant growth-promoting rhizobacteria for improving plant growth and health in challenging conditions: A methodical review.

The genus Bacillus is one of the predominant bacterial genera found in soil, and several species of this genus have been reported from diverse ecological niches. Endowed with tremendous genetic and metabolic diversity, Bacillus spp. serve multiple ecological functions in soil ecosystem from nutrient cycling to conferring stress tolerance to plants. Members of the genus Bacillus are known to have multiple beneficial traits which help the plants directly or indirectly through acquisition of nutrients, overall improvement in growth by production of phytohormones, protection from pathogens and other abiotic stressors. This functionally versatile genus is one of the most commercially exploited bacteria in the agro-biotechnology industry. Still its potential has not been realized sufficiently and requires an emphasis towards translating the relevant technologies from laboratory to land for the benefit of mankind.

https://sfamjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/jam.14506

Bacillus species in soil as a natural resource for plant health and nutrition

Being sessile in nature, plants have to withstand various adverse environmental stress conditions including both biotic and abiotic stresses. Comparatively, abiotic stresses such as drought, salinity, high temperature and cold pose major threat to agriculture by negatively impacting plant growth and yield worldwide. Rice is one of the most widely consumed staple cereals across the globe, the production and productivity of which is also severely affected by different abiotic stresses. Therefore, several crop improvement programs are directed towards developing stress tolerant rice cultivars either through marker assisted breeding or transgenic technology. Alternatively, some known rhizospheric competent bacteria are also known to improve plant growth during abiotic stresses. A plant growth promoting rhizobacteria (PGPR), Bacillus amyloliquefaciens NBRI-SN13 (SN13) was previously reported by our lab to confer salt stress tolerance to rice seedlings. However, the present study investigates the role of SN13 in ameliorating various abiotic stresses such as salt, drought, desiccation, heat, cold, and freezing on a popular rice cv. Saryu-52 under hydroponic growth conditions. Apart from this, seedlings were also exogenously supplied with abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA) and ethephon (ET) to study the role of SN13 in phytohormone-induced stress tolerance as well as its role in abiotic and biotic stress cross-talk. All abiotic stresses and phytohormone treatments significantly affected various physiological and biochemical parameters like membrane integrity and osmolyte accumulation. SN13 also positively modulated stress-responsive gene expressions under various abiotic stresses and phytohormone treatments suggesting its multifaceted role in cross-talk among stresses and phytohormones in response to PGPR. To the best of our knowledge, this is the first report on detailed analysis of plant growth promotion and stress alleviation by a PGPR in rice seedlings subjected to various abiotic stresses and phytohormone treatments for 0, 1, 3, 10 and 24 h.

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Bacillus amyloliquefaciens Confers Tolerance to Various Abiotic Stresses and Modulates Plant Response to Phytohormones through Osmoprotection and Gene Expression Regulation in Rice.

Plant growth promoting rhizobacteria (PGPR) are diverse, naturally occurring bacteria that establish a close association with plant roots and promote the growth and immunity of plants. Established mechanisms involved in PGPR-mediated plant growth promotion include regulation of phytohormones, improved nutrient availability, and antagonistic effects on plant pathogens. In this study, we isolated a bacterium from the rhizospheric soil of a soybean field in Chungcheong buk-do, South Korea. Using 16S rRNA sequencing, the bacterium was identified as Bacillus aryabhattai strain SRB02. Here we show that this strain significantly promotes the growth of soybean. Gas chromatography-mass spectrometry analysis showed that SRB02 produced significant amounts of abscisic acid, indole acetic acid, cytokinin and different gibberellic acids in culture. SRB02-treated soybean plants showed significantly better heat stress tolerance than did untreated plants. These plants also produced consistent levels of ABA under heat stress and exhibited ABA-mediated stomatal closure. High levels of IAA, JA, GA12, GA4, and GA7, were recorded in SRB02-treated plants. These plants produced longer roots and shoots than those of control plants. B. aryabhattai SRB02 was found to be highly tolerant to oxidative stress induced by H2O2 and MV potentiated by high catalase (CAT) and superoxide dismutase (SOD) activities. SRB02 also tolerated high nitrosative stress induced by the nitric oxide donors GSNO and CysNO. Because of these attributes, B. aryabhattai SRB02 may prove to be a valuable resource for incorporation in biofertilizers and other soil amendments that seek to improve crop productivity.

/pdf/bacillus-aryabhattai-srb02-tolerates-oxidative-and-mqcuj3e94w.pdf

Bacillus aryabhattai SRB02 tolerates oxidative and nitrosative stress and promotes the growth of soybean by modulating the production of phytohormones

In the soil ecosystem, microbial diversity exists and these diverse organisms interact with plant roots and influence the physicochemical properties of plants. Some of these diverse microorganisms can cause diseases or can provide beneficial interactions with plants. Rhizobacteria are well-known beneficial microorganism that colonize the plant root zone (rhizosphere) and are referred to as plant growth-promoting rhizobacteria (PGPR) that contribute to the promotion of plant growth either directly or indirectly. PGPRs are also known for their biocontrol abilities. Sclerotinia sclerotiorum, an Ascomycetous soil inhabiting fungus, causes white rot disease in cucumbers. This disease results in the loss of millions of dollars annually. The current study was conducted to isolate naturally occurring soil inhabiting bacteria that may promote plant growth under diseased conditions and also antagonize the pathogen. The isolated LH4 strain was identified as Streptomyces sp. by 16S rRNA sequencing and phylogenetic analysis. The plant growth promoting effects and the antifungal antagonistic activities against Sclerotinia sclerotiorum were confirmed by measuring enzymatic activity of LH4 and demonstration in planta. In addition, Streptomyces sp. LH4 pure culture application exhibited significant growth inhibition of S. sclerotiorum in cucumber. Analysis of the major hormones related to pathogen defense; the jasmonic acid, and salicylic acid, showed that the modulation of these two hormones increased disease resistance in cucumber. The present study suggests a possible dual role of Streptomyces sp. LH4 as functional material for bio-fertilizer and biocontrol against pathogens.

Streptomyces sp. LH 4 promotes plant growth and resistance against Sclerotinia sclerotiorum in cucumber via modulation of enzymatic and defense pathways

This study identified the volatile organic compounds in the essential oils that are extracted from Chrysanthemum indicum Linne (C. indicum Linne) and investigated the effects of the inhalation of these compounds. We detected a total of 41 volatile organic compounds, including 32 hydrocarbons, four acids, three alcohols, two ketones, and one aldehyde. In a sniffing test, seven types of volatile organic compounds were identified. Furthermore, the volatile organic compounds in C. indicum Linne that were identified were found to be derived from 1,8-cineole and camphor. After inhalation of the essential oils, the subjects' systolic blood pressure and heart rate decreased. This indicates that inhalation of the essential oils extracted from C. indicum Linne provides mental and physical relaxation. We examined the changes in electroencephalogram findings that are observed after C. indicum Linne essential oil inhalation. An increase in theta and alpha waves, which usually appear during relaxation, as well as a decrease in beta and gamma waves, which appear during brain activity such as excessive attention, were noted. These results indicate that C. indicum Linne essential oil inhalation helps to reduce blood pressure and may provide mental and physical relaxation.

https://www.mdpi.com/1420-3049/23/8/2063/pdf

Effect of Volatile Organic Chemicals in Chrysanthemum indicum Linné on Blood Pressure and Electroencephalogram.

병풀(Centella asiatica L. Urban)은 피부상처의 치료제 등의 원료로 해마다 해외 수입량은 증가하고 있으나 국내의 자생하는 Centella asiatica종의 조사 및 재배에 관한 연구는 극히 미진하다. 따라서 본 연구는 경상남도 합천의 농가에서 재배중인 국내 자생종인 병풀에 대하여 항균성, 항염증 등을 조사하고, 피부의 상처 및 노화와 관련된 미백효능과 주름개선효과 등에 관한 기초 실험을 수행한 결과 항균 및 항염증 효능은 메탄올 추출물 그리고 미백효능은 물로 추출한 경우에 가장 높은 효능을 확인 할 수 있었으며 보다 상세하게 설명하면 다음과 같다. 7종의 세균과 1종의 곰팡이에 대하여 50% 메탄올로 추출한 병풀 추출물을 처리한 결과 대부분의 세균들은 대조군으로 처리한 오미자 추출물군과 비교하여 유사하거나 낮은 수준의 유의한 항균력을 나타내었으나 S. pyogenes은 유일하게 병풀추출물에서만 항균력을 보였다. 곰팡이인 C. albicans는 병풀과 오미자 모두의 처리에 대하여 항균활성을 확인 할 수가 없었다. Raw 264.7세포를 이용한 항염증효능을 조사한 결과 50%메탄올로 추출한 추출물을 농도별로 처리한 결과 대조구에 비하여 50% 이상의 산화질소 생성량이 감소함을 확인 할 수 있었다. 한편 B16F10세포주를 이용한 미백효능을 조사한 결과에서는 물로 추출한 추출물을 처리한 결과 대조구에 비하여 멜라닌의 농도가 약 20%까지 감소하였음을 확인하였다. NHDF세포를 이용하여 병풀추출물을 처리한 결과 주름개선효능의 지표에 해당하는 MMP-1의 급격한 감소율을 나타내는 처리농도(400 ppm)를 확인하였으나 강한 세포독성도 동시에 확인이 되어 향후 추가연구가 필요한 것으로 조사되었다.

Analysis of antibacterial, anti-inflammatory, and skin-whitening effect of Centella asiatica (L.) Urban

http://koreascience.or.kr:80/article/JAKO201828138053913.pdf

Dong Yeol Lee

Papers

Bacillus aryabhattai SRB02 tolerates oxidative and nitrosative stress and promotes the growth of soybean by modulating the production of phytohormones

Streptomyces sp. LH 4 promotes plant growth and resistance against Sclerotinia sclerotiorum in cucumber via modulation of enzymatic and defense pathways

Effect of Volatile Organic Chemicals in Chrysanthemum indicum Linné on Blood Pressure and Electroencephalogram.

Analysis of antibacterial, anti-inflammatory, and skin-whitening effect of Centella asiatica (L.) Urban

Analysis of Triterpene Glycoside Levels and Antioxidant Activity in the Different Shoot Tissues of Centella asiatica (L.) Urban