Responses of wheat plants to interactions of 24-epibrassinolide and Glomus mosseae in saline condition

Promotion of Ca2+ Accumulation in Roots by Exogenous Brassinosteroids as a Key Mechanism for Their Enhancement of Plant Salt Tolerance: A Meta-Analysis and Systematic Review

Brassinosteroids (BRs), the sixth major phytohormone, can regulate plant salt tolerance. Many studies have been conducted to investigate the effects of BRs on plant salt tolerance, generating a large amount of research data. However, a meta-analysis on regulating plant salt tolerance by BRs has not been reported. Therefore, this study conducted a meta-analysis of 132 studies to elucidate the most critical physiological mechanisms by which BRs regulate salt tolerance in plants from a higher dimension and analyze the best ways to apply BRs. The results showed that exogenous BRs significantly increased germination, plant height, root length, and biomass (total dry weight was the largest) of plants under salt stress. There was no significant difference between seed soaking and foliar spraying. However, the medium method (germination stage) and stem application (seedling stage) may be more effective in improving plant salt tolerance. BRs only inhibit germination in Solanaceae. BRs (2 μM), seed soaking for 12 h, and simultaneous treatment with salt stress had the highest germination rate. At the seedling stage, the activity of Brassinolide (C28H48O6) was higher than that of Homobrassinolide (C29H50O6), and post-treatment, BRs (0.02 μM) was the best solution. BRs are unsuitable for use in the germination stage when Sodium chloride is below 100 mM, and the effect is also weakest in the seedling stage. Exogenous BRs promoted photosynthesis, and antioxidant enzyme activity increased the accumulation of osmoregulatory and antioxidant substances and reduced the content of harmful substances and Na+, thus reducing cell damage and improving plant salt tolerance. BRs induced the most soluble protein, chlorophyll a, stomatal conductance, net photosynthetic rate, Glutathione peroxidase, and root-Ca2+, with BRs causing Ca2+ signals in roots probably constituting the most important reason for improving salt tolerance. BRs first promoted the accumulation of Ca2+ in roots, which increased the content of the above vital substances and enzyme activities through the Ca2+ signaling pathway, improving plant salt tolerance.

Exogenous 24-epibrassinolide promoted growth and nitrogen absorption and assimilation efficiency of apple seedlings under salt stress

Introduction

High salinity significantly hampers global agricultural productivity. Plants typically undergo lower nitrogen utilization efficiency (NUE) under salt stress. As an active byproduct from brassinolide biosynthesis, 24-epibrassinolide (EBR) is involved in regulating the stress-treated plant N absorption and assimilation. However, the exogenous EBR application effects' on N absorption and assimilation in apple exposed to the salt-stressed condition remains unclear.

Methods

We sprayed exogenous EBR (0.2 mg L^-1) on apple dwarf rootstock (M9T337) seedlings (growing hydroponically) under salt (NaCl) stress in a growth chamber. We analyzed the seedling development, photosynthesis and its-mediated C fixation, N ( NO 3 - ) absorption and assimilation in reponse to exogenous EBR application under salt stress.

Results

The findings demonstrated that NaCl stress greatly hampered seedlings' root growth and that exogenous EBR application obviously alleviated this growth suppression. Exogenous EBR-treated plants under NaCl stress displayed the more ideal root morphology and root activity, stronger salt stress tolerance and photosynthetic capacity as well as higher C- and N-assimilation enzyme activities, NO 3 - ion flow rate and nitrate transporter gene expression level than did untreated plants. Furthermore, the results of isotope labeling noted that exogenous EBR application also enhanced ¹³C-photoassimilate transport from leaves to roots and ¹⁵ NO 3 - transport from roots to leaves under NaCl stress.

Conclusion

Our findings imply that exogenous EBR application, through strengthening photosynthesis, C- and N-assimilation enzyme activities, nitrate absorption and transport as well as synchronized optimizing the distribution of seedlings' C and N, has a fundamental role in improving NUE in apple rootstock seedlings under salt stress.

Brassinolide improves the tolerance of Malus hupehensis to alkaline stress

Malus hupehensis is one of the most widely used apple rootstocks in china but is severely damaged by alkaline soil. Alkaline stress can cause more serious harmful effects on apple plants than salt stress because it also induces high pH stress except for ion toxicity, osmotic stress, and oxidative damage. Brassinolide (BL) plays important roles in plant responses to salt stress. However, its role and function mechanism in apple plants in response to alkaline stress has never been reported. This study showed that applying exogenous 0.2 mg/L BL significantly enhanced the resistance of M. hupehensis seedlings to alkaline stress. The main functional mechanisms were also explored. First, exogenous BL could decrease the rhizosphere pH and promote Ca²⁺ and Mg²⁺ absorption by regulating malic acid and citric acid contents and increasing H⁺ excretion. Second, exogenous BL could alleviate ion toxicity caused by alkaline stress through enhancing Na⁺ efflux and inhibiting K⁺ expel and vacuole compartmentalization. Last, exogenous BL could balance osmotic stress by accumulating proline and reduce oxidative damage through increasing the activities of antioxidant enzymes and antioxidants contents. This study provides an important theoretical basis for further analyzing the mechanism of exogenous BL in improving alkaline tolerance of apple plants.

Metabolomic Profiling of Dongxiang Wild Rice Under Salinity Demonstrates the Significant Role of Amino Acids in Rice Salt Stress

Dongxiang common wild rice is a precious rice germplasm resource for the study and improvement of salt tolerance in rice.The metabolism profile of Dongxiang wild rice (DXWR) under salinity was determined by high performance liquid chromatography-mass spectrometry (HPLC-MS) to find differential metabolites and screen potential biomarkers for salt-tolerant rice varieties. A global untargeted metabolism analysis showed 4,878 metabolites accumulated in seedlings of Dongxiang wild rice. Principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) results provided a clear metabolism discrimination between DXWR under control and DXWR under salinity. A total of 90 metabolites were significantly changed (49 upregulated and 41 downregulated) under salinity, of which the largest increase was in DL-2-Aminoadipic acid (27.08-fold) and the largest decrease was in L-Carnitine (0.014-fold). Amino acids and nuclear glycosides were mainly upregulated, while carbohydrates and organic acids were mainly downregulated in the salt-treated group. Among the top 10 upregulated metabolites, five kinds of differential metabolites were amino acids. According to the survival rates of the seedlings under salinity, we selected three backcross inbred lines of DXWR with survival rates above 80% as salt-tolerant progenies (pro-DS) and three backcross inbred lines with survival rates below 10% as non-salt-tolerant progenies (pro-NDS) for an amino acid change analysis. This analysis found that the change in L-Asparagine (2.59-fold) was the biggest between pro-DS and pro-NDS under salinity, revealing that the contents of L-Asparagine may be one of the indices we can use to evaluate the salt tolerance of rice varieties.

Exogenous Brassinolide Alleviates Salt Stress in Malus hupehensis Rehd. by Regulating the Transcription of NHX-Type Na+(K+)/H+ Antiporters

Brassinolide (BL) mediates various physiological processes and improves plant tolerance to abiotic stresses. However, the effects and mechanism of exogenous BL on the salt tolerance of apple seedlings remain unclear. Herein, we investigated the role of BL in the salt stress response of Malus hupehensis Rehd., a widely grown apple rootstock. Salt-stressed apple seedlings showed significant decline in chlorophyll content and photosynthetic rate, and the application of 0.2 mg/L exogenous BL alleviated salt stress and maintained photosynthetic capacity. Exogenous BL application can strengthen the activities of superoxide dismutase and catalase and thereby eliminates reactive oxygen species (ROS) production induced by salt stress and promote the accumulation of proline and soluble sugar, thus maintaining osmotic balance. Furthermore, exogenous BL application decreased Na⁺ accumulation and increased K⁺ content in shoots and roots under salt stress by regulating the expression levels of Na⁺(K⁺)/H ⁺ antiporter genes (MhNHXs). MhBZR1 and MhBZR2, which are the key transcription factors in the BR signal transduction pathway, can directly bind to the promoter of MhSOS1 and MhNHX4-1, respectively, and inhibit their expression. Our findings would provide a theoretical basis for analyzing the mechanism of exogenous BL application on the salt tolerance of apples.

Brassinosteroids Affect the Symbiosis Between the AM Fungus Rhizoglomus irregularis and Solanaceous Host Plants

Together with several proteins involved in brassinosteroid (BR) signaling and synthesis, the membrane steroid binding protein 1 (MSBP1) was identified within the interactome of the sucrose transporter of tomato (SlSUT2). We asked whether MSBP1 is also involved in BR signaling as assumed for the AtMSBP1 protein from Arabidopsis and whether it impacts root colonization with arbuscular mycorrhizal (AM) fungi in a similar way as shown previously for SlSUT2. In addition, we asked whether brassinosteroids per se affect efficiency of root colonization by AM fungi. We carried out a set of experiments with transgenic tobacco plants with increased and decreased MSBP1 expression levels. We investigated the plant and the mycorrhizal phenotype of these transgenic plants and tested the involvement of MSBP1 in BR metabolism by application of epi-brassinolide and brassinazole, an inhibitor of BR biosynthesis. We show that the phenotype of the transgenic tobacco plants with increased or reduced MSBP1 expression is consistent with an inhibitory role of MSBP1 in BR signaling. MSBP1 overexpression could be mimicked by brassinazole treatment. Interestingly, manipulation of MSBP1 expression in transgenic tobacco plants not only affected plant growth and development, but also the host plant responses toward colonization with AM fungi, as well as arbuscular architecture. Moreover, we observed that brassinosteroids indeed have a direct impact on the nutrient exchange in AM symbiosis and on the biomass production of colonized host plants. Furthermore, arbuscular morphology is affected by changes in MSBP1 expression and brassinolide or brassinazole treatments. We conclude that host plant growth responses and nutrient exchange within the symbiosis with AM fungi is controlled by brassinosteroids and might be impeded by the MSBP1 protein.

Exogenous application of calcium to 24-epibrassinosteroid pre-treated tomato seedlings mitigates NaCl toxicity by modifying ascorbate-glutathione cycle and secondary metabolites

The present study tested the efficacy of 24-epibrassinolide (EBL) and calcium (Ca) for mediating salinity tolerance in tomato. Salinity stress affected the morphological parameters of tomato as well as leaf relative water content (LRWC), photosynthetic and accessory pigments, leaf gas exchange parameters, chlorophyll fluorescence and the uptake of essential macronutrients. The salt (NaCl) treatment induced oxidative stress in the form of increased Na+ ion concentration by 146%, electrolyte leakage (EL) by 61.11%, lipid peroxidation (MDA) 167% and hydrogen peroxide (H2O2) content by 175%. Salt stress also enhanced antioxidant enzyme activities including those in the ascorbate-glutathione cycle. Plants treated with EBL or Ca after salt exposure mitigated the ill effects of salt stress, including oxidative stress, by reducing the uptake of Na+ ions by 52%. The combined dose of EBL + Ca reversed the salt-induced changes through an elevated pool of enzymes in the ascorbate-glutathione cycle, other antioxidants (superoxide dismutase, catalase), and osmoprotectants (proline, glycine betaine). Exogenously applied EBL and Ca help to optimize mineral nutrient status and enable tomato plants to tolerate salt toxicity. The ability of tomato plants to tolerate salt stress when supplemented with EBL and Ca was attributed to modifications to enzymatic and non-enzymatic antioxidants, osmolytes and metabolites.

24-Epibrassinolide; an active brassinolide and its role in salt stress tolerance in plants: A review

Salt stress is one of most dramatic abiotic stresses, reduces crop yield significantly. Application of hormones proved effective salt stress ameliorating approach. 24-Epibrassinolide (EBL), an active by-product from brassinolide biosynthesis shows significant salt stress tolerance in plants. EBL application improves plant growth and development under salt stress by playing as signalling compound in different metabolic and physiological processes. This article compiles all identified ways by which EBL improves plant growth and enhances crop yield. Furthermore, EBL enhances photosynthetic rate, reduces ROS production and plays important role in ionic homeostasis. Furthermore EBL-induced salt stress tolerance suggest that complex transcriptional and translational reprogramming occurs in response to EBL and salt stress therefore transcriptional and translational changes in response to EBL application are also discussed in this article.

Abiotic Stress Signaling in Wheat - An Inclusive Overview of Hormonal Interactions During Abiotic Stress Responses in Wheat

Rapid global warming directly impacts agricultural productivity and poses a major challenge to the present-day agriculture. Recent climate change models predict severe losses in crop production worldwide due to the changing environment, and in wheat, this can be as large as 42 Mt/°C rise in temperature. Although wheat occupies the largest total harvested area (38.8%) among the cereals including rice and maize, its total productivity remains the lowest. The major production losses in wheat are caused more by abiotic stresses such as drought, salinity, and high temperature than by biotic insults. Thus, understanding the effects of these stresses becomes indispensable for wheat improvement programs which have depended mainly on the genetic variations present in the wheat genome through conventional breeding. Notably, recent biotechnological breakthroughs in the understanding of gene functions and access to whole genome sequences have opened new avenues for crop improvement. Despite the availability of such resources in wheat, progress is still limited to the understanding of the stress signaling mechanisms using model plants such as Arabidopsis, rice and Brachypodium and not directly using wheat as the model organism. This review presents an inclusive overview of the phenotypic and physiological changes in wheat due to various abiotic stresses followed by the current state of knowledge on the identified mechanisms of perception and signal transduction in wheat. Specifically, this review provides an in-depth analysis of different hormonal interactions and signaling observed during abiotic stress signaling in wheat.