Endogenous Salicylic Acid Levels Research Articles

Salicylic acid mitigates 'Hayward' kiwifruit chilling injury by regulating hormone and proline metabolism, as well as maintaining cellular structure

The 'Hayward' kiwifruit is extremely susceptible to chilling injury (CI) during the late stages of cold storage, thus limiting its storage quality and life. Therefore, mitigating the losses caused by CI is imperative. Salicylic acid (SA) has been demonstrated to mitigate CI in fruit and vegetables. In this study, we conducted a comparative analysis of proline metabolism, key endogenous hormone levels, as well as the effects on cell structure and membrane lipid oxidation in kiwifruit treated with 1 mM SA during low-temperature storage. The results showed that SA could attenuate lipoxygenase (LOX) activity, enhance catalase (CAT) activity, suppress the elevation of malondialdehyde (MDA) content, mitigate starch granule degradation in cells, and preserve cell structure integrity. Moreover, SA was found to enhance proline biosynthesis by activating ornithine transaminase (OAT) and pyrroline-5-carboxylate synthase (P5CS) while concurrently suppressing proline dehydrogenase (PDH) activity. Additionally, exogenous SA increased endogenous levels of both SA and abscisic acid (ABA), while simultaneously decreasing the concentration of gibberellic acid (GA) in fruit. In conclusion, exogenous SA treatment could alleviate the development of CI in kiwifruit by maintaining cell structure, promoting proline synthesis, and balancing endogenous hormone content. Our study offers a theoretical foundation for understanding the mechanism by which SA mitigates cold damage in kiwifruit, and provides novel insights into the low-temperature preservation of kiwifruit.

Halotolerant endophytic bacteria alleviate salinity stress in rice (oryza sativa L.) by modulating ion content, endogenous hormones, the antioxidant system and gene expression

Excessive salinity reduces crop production and negatively impacts agriculture worldwide. We previously isolated endophytic bacterial strains from two halophytic species: Artemisia princeps and Chenopodium ficifolium. We used three bacterial isolates: ART-1 (Lysinibacillus fusiformis), ART-10 (Lysinibacillus sphaericus), and CAL-8 (Brevibacterium pityocampae) to alleviate the impact of salinity stress on rice. The impact of 160 mM NaCl salinity on rice was significantly mitigated following inoculation with these bacterial strains, resulting in increased growth and chlorophyll content. Furthermore, OsNHX1, OsAPX1, OsPIN1 and OsCATA expression was increased, but OsSOS expression was decreased. Inductively coupled plasma mass spectrometry (ICP-MS) revealed reduced K+ and Na+ levels in shoots of bacteria-inoculated plants, whereas that of Mg2+ was increased. Bacterial inoculation reduced the content of total flavonoids in rice leaves. Salinized plants inoculated with bacteria showed reduced levels of endogenous salicylic acid (SA) and abscisic acid (ABA) but increased levels of jasmonic acid (JA). In conclusion, the bacterial isolates ART-1, ART-10, and CAL-8 alleviated the adverse effect of salinity on rice growth, which justifies their use as an eco-friendly agricultural practice.

Microbial Filtrates Improved Growth Parameters of In vitro PVX Infected Potato Plantlets

This study focuses on utilizing the phenomenon of systemic acquired resistance (SAR) to control plant viruses and increased growth in vitro. The study demonstrated the induction of SAR in potato plantlets against Potato Virus X by using bacterial culture filtrates invitro. These biotic inducers included Pseudomonas spp. and Bacillus spp. The study observed the occurrence of induced resistance and enhanced growth in potato plantlets treated with culture filtrates containing these microorganisms. This was evident through a reduction in PVX infection, disease severity and associated biochemical changes (such as elevated levels of endogenous salicylic acid, protein content, chlorophyll content, peroxidase and polyphenol oxidase activities), as well as improvements in growth parameters.

Salicylic acid alleviates Zn-induced inhibition of growth via enhancing antioxidant system and glutathione metabolism in alfalfa

Zinc (Zn) is considered as one of the heavy metal pollutants in soil affecting agriculture. Salicylic acid (SA) is an important phytohormone that can mitigate effects against various abiotic stresses in plants, however, its exploration to improve Zn stress tolerance in alfalfa plants is still elusive. Thus, in the present study, exogenous SA treatment was conducted on alfalfa plants under Zn stress. The effects of exogenous SA on the physiological effects of alfalfa plants and the expression levels related genes were studied. This study tested the biomass, relative water content, chlorophyll levels, photosynthetic capacity, proline and soluble sugar contents, detected the activity of antioxidant enzymes (such as peroxidase and superoxide dismutase), glutathione biosynthesis, and endogenous SA levels, and quantified the genes associated with the antioxidant system and glutathione metabolism-mediated Zn stress. The results showed that exogenous SA could elevate the physiological adaptability of alfalfa plants through enhancing photosynthesis, proline and soluble sugar levels, stimulating antioxidant system and glutathione metabolism, and inducing the transcription level of related genes, thereby diminishing oxidative stress, inhibiting excessive Zn accumulation of alfalfa plants, increasing tolerance to Zn stress, and reducing the toxicity of Zn. Collectively, the application of SA alleviates Zn toxicity in alfalfa plants. The findings gave first insights into the regulatory mechanism of the Zn stress tolerance of alfalfa by exogenous SA and this might have positive implications for managing other plants which are suffering Zn stress.

Simultaneous editing of two DMR6 genes in grapevine results in reduced susceptibility to downy mildew.

The reduction of pesticide treatments is of paramount importance for the sustainability of viticulture, and it can be achieved through a combination of strategies, including the cultivation of vines (Vitis vinifera) that are resistant or tolerant to diseases such as downy mildew (DM). In many crops, the knock-out of Downy Mildew Resistant 6 (DMR6) proved successful in controlling DM-resistance, but the effect of mutations in DMR6 genes is not yet known in grapevine. Today, gene editing serves crop improvement with small and specific mutations while maintaining the genetic background of commercially important clones. Moreover, recent technological advances allowed to produce non-transgenic grapevine clones by regeneration of protoplasts edited with the CRISPR/Cas9 ribonucleoprotein. This approach may revolutionize the production of new grapevine varieties and clones, but it requires knowledge about the targets and the impact of editing on plant phenotype and fitness in different cultivars. In this work we generated single and double knock-out mutants by editing DMR6 susceptibility (S) genes using CRISPR/Cas9, and showed that only the combined mutations in VviDMR6-1 and VviDMR6-2 are effective in reducing susceptibility to DM in two table-grape cultivars by increasing the levels of endogenous salicylic acid. Therefore, editing both genes may be necessary for effective DM control in real-world agricultural settings, which could potentially lead to unwanted phenotypes. Additional research, including trials conducted in experimental vineyards, is required to gain a deeper understanding of DMR6-based resistance.

Стрес-протекторні та регуляторні властивості саліцилової кислоти і перспективи її використання в рослинництві

Salicylic acid (SA), as a secondary phenolic metabolite with phytohormonal activity, is an important component of the plant defense system against biotic and abiotic stresses. The scale of industrial synthesis of SA in the world is constantly growing, it is used as an intermediate for the synthesis of drugs and dyes, it is also used in cosmetology, food industry, plant biotechnology, etc. Recently, it has been considered as a promising growth-regulating agent in crop production for decreasing harmful effects of biotic and abiotic stresses in plants. Over the past two decades, numerous data have been published concerning the metabolic pathways of SA synthesis and its signaling in plant immunity. It regulates and affects various stages of plant ontogenesis and metabolism: seed germination, flowering, stomatal movements, pigment synthesis, photosynthesis and respiration, ethylene biosynthesis, thermoregulation, the activity of antioxidant enzymes, nutrient absorption, membrane integrity and functioning, nodulation in legumes, synthesis of secondary metabolites, general growth and development of plants. Numerous studies have confirmed that endogenous SA and/or its derivatives are involved in stress responses to heavy metals (HMs), hyper- and hypothermia, salinity, water deficiency, and, primarily, pathogenic infections. In parallel with fundamental studies of regulatory functions of SA and/or its derivatives, new ways of their exogenous application are constantly discovered. The use of low concentrations of exogenous SA (0.1–0.5 mM) for seed priming or foliar treatment is reported as an economically viable alternative approach for increasing plant tolerance from both economic and environmental points of view. Exogenous SA leads to an increase in endogenous SA levels that induces plant adaptive responses by changing phytohormonal status, increased synthesis of a number of secondary metabolites (alkaloids, cyanogenic glycosides, phenolics, terpenes), by increasing activity of antioxidant enzymes. One of the main advantages of using SA in crop production is the ability to reduce the dosage of pesticides and fertilizers that are potentially harmful to the environment and human health. It is also reported that the use of SA in some cases may lead to negative results – growth retardation, sterility, and yield decrease; the causes of this phenomenon are actively investigated. Further studies are necessary to clarify the mechanisms of exogenic SA action and its use on various crops in different growing conditions. This review aims to analyze the recent data on SA, crop production, and biotechnology areas where it is possible to effectively apply the SA and/or its derivatives.

Nucleoredoxin gene SINRX1 negatively regulates tomato immunity by activating SA signaling pathway

The tomato (Solanum lycopersicum) is widely consumed globally and renowned for its health benefits, including the reduction of cardiovascular disease and prostate cancer risk. However, tomato production faces significant challenges, particularly due to various biotic stresses such as fungi, bacteria, and viruses. To address this challenges, we employed the CRISPR/Cas9 system to modify the tomato NUCLEOREDOXIN (SlNRX) genes (SlNRX1 and SlNRX2) belonging to the nucleocytoplasmic THIOREDOXIN subfamily. CRISPR/Cas9-mediated mutations in SlNRX1 (slnrx1) plants exhibited resistance against bacterial leaf pathogen Pseudomonas syringae pv. maculicola (Psm) ES4326, as well as the fungal pathogen Alternaria brassicicola. However, the slnrx2 plants did not display resistance. Notably, the slnrx1 demonstrated elevated levels of endogenous salicylic acid (SA) and reduced levels of jasmonic acid after Psm infection, in comparison to both wild-type (WT) and slnrx2 plants. Furthermore, transcriptional analysis revealed that genes involved in SA biosynthesis, such as ISOCHORISMATE SYNTHASE 1 (SlICS1) and ENHANCED DISEASE SUSCEPTIBILITY 5 (SlEDS5), were upregulated in slnrx1 compared to WT plants. In addition, a key regulator of systemic acquired resistance, PATHOGENESIS-RELATED 1 (PR1), exhibited increased expression in slnrx1 compared to WT. These findings suggest that SlNRX1 acts as a negative regulator of plant immunity, facilitating infection by the Psm pathogen through interference with the phytohormone SA signaling pathway. Thus, targeted mutagenesis of SlNRX1 is a promising genetic means to enhance biotic stress resistance in crop breeding.

Endogenous Salicylic acid Estimation in Wheat leaves treated with Salicylic acid and infected with Alternaria triticina

This study was aime to measure the accumulation of endogenous salicylic acid, as indicator for systemic acquired re-sistance of wheat plants of “Utique” variety. The plant was sprayed with salicylic acid (SA) or water as control, at the five-leaf stage, later infected with leaf blight caused by Alternaria triticina. Leaf samples were removed after 10, 20, and 30 days of inoculation to test their endogenous content of salicylic acid as it is the primary internal signal indicating the emergence of systemic acquired resistance in plants, by the spectrophotometer measuring. Endogenous SA values were ascending dramatically from 10 days to 20 days and maximum with 30th day significantly, while control plants exhibit lower values in all day periods, insignificantly. SA treatments proved reduction in disease incidence after 10 days with 54% and after 20 days with 64%, while after 30 days the reduction recorded high percentage of 80%. In comparison between the time intervals, disease severity was clearly reduction and reached to 83% after 10 days of inoculation then decreased to 72% for both 20th and maintained its stability on the 30th day of inoculation by 72%. This study was proved the reduction of wheat leaf blight incidence and disease severity as a result of treatment by using 1Millimolar (mM) of SA was leading to accumulation of significant levels of endogenous SA as indicator for internal induced resistance in plant.

Sulfur dioxide improves the thermotolerance of maize seedlings by regulating salicylic acid biosynthesis

Heat stress (HS) has become a serious threat to crop growth and yield. Sulfur dioxide (SO2) is being verified as a signal molecule in regulating the plant stress response. However, it is unknown whether SO2 plays a significant role in the plant heat stress response (HSR). Herein, maize seedlings were pretreated with various concentrations of SO2 and then kept at 45 °C for heat stress treatment, aiming to study the effect of SO2 pretreatment on HSR in maize by phenotypic, physiological, and biochemical analyses. It was found that SO2 pretreatment greatly improved the thermotolerance of maize seedlings. The SO2-pretreated seedlings showed 30–40% lower ROS accumulation and membrane peroxidation, but 55–110% higher activities of antioxidant enzymes than the distilled water-pretreated seedlings under heat stress. Interestingly, endogenous salicylic acid (SA) levels were increased by ∼85% in SO2-pretreated seedlings, as revealed by phytohormone analyses. Furthermore, the SA biosynthesis inhibitor paclobutrazol markedly reduced SA levels and attenuated SO2-triggered thermotolerance of maize seedlings. Meanwhile, transcripts of several SA biosynthesis and signaling, and heat stress-responsive genes in SO2-pretreated seedlings were significantly elevated under HS. These data have demonstrated that SO2 pretreatment increased endogenous SA levels, which activated the antioxidant machinery and strengthened the stress defense system, thereby improving the thermotolerance of maize seedlings under HS. Our current study provides a new strategy for mitigating heat stress damage for safe crop production.

Spermine-Salicylic Acid Interplay Restrains Salt Toxicity in Wheat (Triticum aestivum L.).

Spermine (SPM) and salicylic acid (SA) are plant growth regulators, eliciting specific responses against salt toxicity. In this study, the potential role of 30 mgL-1 SPM and/or 100 mgL-1 SA in preventing salt damage was investigated. Wheat plants were grown under non-saline or saline conditions (6.0 and 12.0 dS m-1) with and without SA and/or SPM foliar applications. Exogenously applied SA and/or SPM alleviated the inhibition of plant growth and productivity under saline conditions by increasing Calvin cycle enzyme activity. Foliage applications also improved ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase activities, which effectively scavenged hydrogen peroxide and superoxide radicals in stressed plants. Furthermore, foliar treatments increased antioxidants such as ascorbate and glutathione, which effectively detoxified reactive oxygen species (ROS). Exogenous applications also increased N, P, and K+ acquisition, roots' ATP content, and H+-pump activity, accompanied by significantly lower Na+ accumulation in stressed plants. Under saline environments, exogenous SA and/or SPM applications raised endogenous SA and SPM levels. Co-application of SA and SPM gave the best response. The newly discovered data suggest that the increased activities of Calvin cycle enzymes, root H+-pump, and antioxidant defense machinery in treated plants are a mechanism for salt tolerance. Therefore, combining the use of SA and SPM can be a superior method for reducing salt toxicity in sustainable agricultural systems.

Salicylic acid treatment inhibits ethylene synthesis and starch-sugar conversion to maintain apple fruit quality during shelf life

Starch and sugars are widely acknowledged as taste determinants, energy substances, and signal molecules in fruits. Salicylic acid (SA) regulates many physiological and biochemical processes during fruit ripening. In this work, we investigated the effects of SA treatment on physiological parameters and SA synthesis, ethylene production, and starch-sugar metabolism of apples during shelf life. Results showed that SA maintained fruit firmness, reduced weight loss, and inhibited starch to sugar conversion during shelf life. The endogenous SA level was increased in SA-treated fruits, mediated by MdPAL, MdICS2, and MdNPR1, thus decreasing MdACS1 and MdACO1 expressions and inhibiting ethylene biosynthesis. Furthermore, the expression of starch and sugar-related genes, MdAMY, MdBam5, MdBam8, MdSPS, MdSUSY, MdNINV, and MdAINV, were inhibited by SA treatment during shelf life. It was inferred that exogenous SA could inhibit ethylene synthesis and starch-sugar conversion, maintain the quality, and prolong the shelf life of apples

Effect of salicylic acid treatment on antioxidant capacity and endogenous hormones in winter jujube during shelf life

This study investigated the effects of exogenous salicylic acid (SA) treatment (0, control; 3 mmol L−1) on the antioxidant and hormone levels of winter jujube during shelf life (20 d) at 4 °C. The results showed that 3 mmol L−1 SA treatment preferably maintained firmness, color, titratable acidity, and total soluble solids, and effectively reduced the respiratory intensity and TSS/TA value (13.08%) of the fruit. Compared with the control group, the SA group had a higher content of sucrose (14.03%) and malic acid (29.13%). Meanwhile, SA reduced the accumulation of H2O2 (27.73%) and O2− (45.44%) by enhancing the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and the content of antioxidant substances (ascorbic acid, total phenols, total flavonoids, and glutathione) in the fruit. In addition, 3 mmol L−1 SA treatment led to higher levels of endogenous abscisic acid (18.49%) and SA (20.47%) in fruit, and lower concentration of jasmonic acid (42.68%), but had a weak effect on indole acetic acid levels.

A low concentration of exogenous salicylic acid enhances cold tolerance in Hami melons (Cucumis melo var. saccharinus) by modulating salicylic acid-response CmGST genes

Long-term cold storage of Hami melons (Cucumis melo var. saccharinus) induces severe chilling injuries, downgrading their storage quality. Three different concentrations (1, 3, and 9 mM) of exogenous salicylic acid (SA) were applied under cold stress conditions (0.5 ± 0.5 °C) to prolong the shelf-life of cold-sensitive ‘Golden Empress-308′ (GE-melon) Hami melons. Afterward, the phenotypic index, bioinformatics of CmGSTs, expression patterns of CmGSTs, endogenous SA content, molecular docking, and molecular dynamics simulation were investigated. The phenotypic index indicated that low concentrations (1 and 3 mM) of SA ameliorated chilling injuries, whereas a high concentration of SA (9 mM) treatment adversely affected the GE-melons. The RT-qPCR analysis determined that SA treatment induced five out of seven CmGST-containing SA-response cis-elements. The content of endogenous SA was elevated by exogenous SA. Interestingly, both high and low levels of endogenous SA promoted chilling injuries in GE-melons under cold stress conditions. Furthermore, molecular docking and molecular dynamics simulation signaled that SA bound to the target CmGSTs in a stable conformation. In conclusion, administration of a low concentration of SA enhances cold tolerance in Hami melons by modulating the SA-responsive CmGSTs under cold stress conditions.

Antioxidant Machinery and Glyoxalase System Regulation Confers Salt Stress Tolerance to Wheat (Triticum aestivum L.) Plants Treated with Melatonin and Salicylic Acid

Plant growth regulators melatonin (MT) and salicylic acid (SA) have potent roles in plant salt tolerance. However, only a few reports have studied the influence of their combined treatment on plant salt tolerance. The current study, as a first investigation, was aimed to evaluate the effect of MT and SA combined treatment on the antioxidant and glyoxalase defense machineries of salt-stressed wheat plants. In the present study, the potential role of 70 μM MT and/or 75 mg l−1 SA on mitigating salt injury (6.0 and 12.0 dS m−1 salinity levels) was investigated in wheat (Triticum aestivum L. cv. Sids 14). Exogenously applied MT and/or SA improved the activity of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and glutathione S-transferase, which effectively scavenged reactive oxygen species (ROS) in stressed plants. Excessive accumulation of the toxic methylglyoxal was reversed via the up-regulation of the glyoxalase system (glyoxalase I and glyoxalase II) and the ascorbate–glutathione cycle. Foliar applications also reduced membrane damage by lowering lipid peroxidation and protein oxidation due to effective ROS detoxification by antioxidants such as ascorbate, glutathione, phenols, and flavonoids. Moreover, exogenous MT and/or SA applications increased endogenous MT and SA levels under both non-saline and saline conditions. The combined treatment of MT and SA yielded the best results. Overall, this combined treatment regulated the antioxidant machinery and glyoxalase system, suggesting a role for it in salt stress mitigation. Therefore, it can be considered as an effective method for reducing salt toxicity in sustainable agricultural systems.

Overexpression of OsGF14f Enhances Quantitative Leaf Blast and Bacterial Blight Resistance in Rice.

Although it is known that rice 14-3-3 family genes are involved in various defense responses, the functions of OsGF14f in response to diseases have not been reported. Here, we showed that the transcription of OsGF14f was significantly induced by leaf blast infection, and the overexpression of OsGF14f quantitatively enhanced resistance to leaf blast and bacterial blight in rice. Further analysis showed that the expression levels of salicylic acid (SA) pathway-associated genes (PAL1, NH1, PR1a and PR10) in the OsGF14f-overexpressing plants, were higher than those in wild-type plants after inoculation with the blast isolate (Magnaporthe oryzae Barr). In addition, the expression level of OsGF14f was significantly induced after SA treatment, and higher endogenous SA levels were observed in the OsGF14f-overexpressing plants compared with that in wild-type plants, especially after blast challenge. Taken together, these results suggest that OsGF14f positively regulates leaf blast and bacterial blight resistance in rice via the SA-dependent signaling pathway.

Phosphorylation of OsTGA5 by casein kinase II compromises its suppression of defense-related gene transcription in rice.

Plants manage the high cost of immunity activation by suppressing the expression of defense genes during normal growth and rapidly switching them on upon pathogen invasion. TGAs are key transcription factors controlling the expression of defense genes. However, how TGAs function, especially in monocot plants like rice with continuously high levels of endogenous salicylic acid (SA) remains elusive. In this study, we characterized the role of OsTGA5 as a negative regulator of rice resistance against blast fungus by transcriptionally repressing the expression of various defense-related genes. Moreover, OsTGA5 repressed PTI responses and the accumulation of endogenous SA. Importantly, we showed that the nucleus-localized casein kinase II (CK2) complex interacts with and phosphorylates OsTGA5 on Ser-32, which reduces the affinity of OsTGA5 for the JIOsPR10 promoter, thereby alleviating the repression of JIOsPR10 transcription and increasing rice resistance. Furthermore, the in vivo phosphorylation of OsTGA5 Ser-32 was enhanced by blast fungus infection. The CK2 α subunit, depending on its kinase activity, positively regulated rice defense against blast fungus. Taken together, our results provide a mechanism for the role of OsTGA5 in negatively regulating the transcription of defense-related genes in rice and the repressive switch imposed by nuclear CK2-mediated phosphorylation during blast fungus invasion.

The salicylic acid mediates selenium-induced tolerance to drought stress in tomato plants

The role of selenium (Se) in mitigating detrimental effects of drought stress on the plants has been reported, but the mechanism is still unclear. In this study, the function of Se fertilization on tomato (Solanum lycopersicum L.) under drought stress was characterized. Our results showed that the growth reduction caused by drought stress was alleviated by application of exogenous Se to a large extent. In addition, the treatment of Se significantly increased the net photosynthetic rate (Pn), transpirational rate (Tr), stomatal conductance (Gs) and water use efficiency (WUE) than in the absence of Se under drought stress treatment. Se addition also significantly inhibited the increase of malondialdehyde (MDA), soluble sugar and proline levels of tomato leaves and produced less reactive oxygen species (ROS) accumulation under drought stress. Furthermore, Se supplementation to the nutrient solution significantly increased the endogenous salicylic acid (SA) and methylated SA (MeSA) levels in tomato roots and promoted the conversion from SA to MeSA in tomato leaves under drought stress conditions via regulating the expression levels of several genes involved in SA biosynthesis and conversion such as PAL1, ICS, SAMT and SABP2. But the pretreatment with ABT (1-aminobenzotriazole, a SA inhibitor) abolished the beneficial effect of Se on drought stress tolerance of plants. These results suggested that Se application promoted photosynthetic efficiency and plant growth, alleviated drought-induced oxidative stress, and increased the endogenous SA levels, thereby imparting drought stress tolerance of tomato plants. This study may provide a theoretical basis for utilization of Se fertilizer to improve the yield and quality of agricultural products under stress.

Application of UV-B radiation for enhancing the accumulation of bioactive phenolic compounds in pigeon pea [Cajanus cajan (L.) Millsp.] hairy root cultures.

UV-B radiation is an ideal elicitation strategy for promoting phytochemical accumulation in plant in vitro cultures, associated with various advantages of easy manipulation, cost-effectiveness, no residue, and instantaneous termination. For the first time, UV-B radiation was used to enhance the production of bioactive phenolic compounds (flavonoids and stilbenes) in pigeon pea hairy root cultures (PPHRCs). The total yield of eight flavonoids (414.95±50.68μg/g DW) in 42-day-old PPHRCs exposed to 4h of UV-B radiation increased by 1.49-fold as against control, whereas the yield of cajaninstilbene acid (6566.01±702.14μg/g DW) in PPHRCs undergoing 10h of UV-B radiation significantly increased by 2.31-fold over control. UV-B radiation was found to induce the oxidative stress in PPHRCs and cause the tissue damage to hairy roots, which improved the levels of endogenous salicylic acid thus triggering the expression of genes involved in phenylpropanoid biosynthesis pathway. And, a regulation competition in metabolic flow dominated by CHS and STS was responsible for the difference in accumulation trends of flavonoids and cajaninstilbene acid. Results of this study not only provide a feasible and simple UV-B supplementation strategy for the enhanced production of bioactive phenolic compounds (especially the high-value cajaninstilbene acid) in PPHRCs, but also contributed to the understanding of photobiological responses related to secondary metabolism.

Salicylic-Acid-Regulated Antioxidant Capacity Contributes to Growth Improvement of Okra (Abelmoschus esculentus cv. Red Balady)

The improvement of crop yield and quality are currently of prime concern to achieve global food security and sustainability. Plant elicitation with salicylic acid (SA) has been shown to play a key role in regulating plant growth and productivity. Here, the effects of foliar SA application (1, 2, and 4 mM) on antioxidant capacity and phenolic metabolism, among other biochemical parameters, were studied in okra leaves. The results showed that SA treatments markedly increase the levels of endogenous free SA and trigger the accumulation of chlorophylls, soluble proteins, proline, antioxidant capacity, and phenolic compounds, alongside the stimulation of the enzymatic activities of phenylalanine ammonia-lyase and peroxidase, with these changes being paralleled by decreased levels of lipid peroxidation. The beneficial effects of SA treatments were also tested on field-grown okra plants. Results revealed that yield-associated agronomic attributes significantly increased upon SA treatments, especially at 2 mM SA. Altogether, these results point to a connection between SA-induced antioxidant system strengthening and crop growth and productivity. Therefore, foliar application of SA seems to be a potent and workable approach to enhance okra crop quality and yield.

Tomato and cotton G protein beta subunit mutants display constitutive autoimmune responses.

Heterotrimeric G protein Gβ‐deficient mutants in rice and maize display constitutive immune responses, whereas Arabidopsis Gβ mutants show impaired defense, suggesting the existence of functional differences between monocots and dicots. Using CRISPR/Cas9, we produced one hemizygous tomato line with a mutated SlGB1 Gβ gene. Homozygous slgb1 knockout mutants exhibit all the hallmarks of autoimmune mutants, including development of necrotic lesions, constitutive expression of defense‐related genes, and high endogenous levels of salicylic acid (SA) and reactive oxygen species, resulting in early seedling lethality. Virus‐induced silencing of Gβ in cotton reproduced the symptoms observed in tomato mutants, confirming that the autoimmune phenotype is not limited to monocot species but is also shared by dicots. Even though multiple genes involved in SA and ethylene signaling are highly induced by Gβ silencing in tomato and cotton, co‐silencing of SA or ethylene signaling components in cotton failed to suppress the lethal phenotype, whereas co‐silencing of the oxidative burst oxidase RbohD can repress lethality. Despite the autoimmune response observed in slgb1 mutants, we show that SlGB1 is a positive regulator of the pathogen‐associated molecular pattern (PAMP)‐triggered immunity (PTI) response in tomato. We speculate that the phenotypic differences observed between Arabidopsis and tomato/cotton/rice/maize Gβ knockouts do not necessarily reflect divergences in G protein‐mediated defense mechanisms.