H2O2 Functions as a Downstream Signal of IAA to Mediate H2S-Induced Chilling Tolerance in Cucumber

An indole-3-acetic acid inhibitor mitigated mild cadmium stress by suppressing peroxide formation in rice seedling roots

Cadmium (Cd) is a widely distributed heavy metal pollutant that is detrimental to growth and development of plants. The secretion of indole-3-acetic acid is one of the defense mechanisms when plants inflict heavy metal stress. This study aimed to explore how 4-phenoxyphenylboronic acid, an effective IAA inhibitor, induces changes in IAA level, Cadmium accumulation, and activation of defense responses in rice seedling roots under different Cadmium concentrations. Our research results show that: 1) root growth was promoted with PPBa addition under mild Cadmium treatment. 2) the root IAA level improved with increasing Cadmium concentration, and PPBa had a significant inhibitory effect on IAA level. 3) PPBa had no effect on the Cadmium accumulation in rice seedling roots. 4) PPBa had a significant inhibitory effect on the generation of H2O2 under mild and moderate Cadmium treatment. 5) PPBa exacerbated the imbalance of osmotic substances in rice seedling roots under severe Cadmium treatment. This study helps us understand the tolerance and endogenous regulation of plants to heavy metal stress.

Hydrogen Sulfide in the Oxidative Stress Response of Plants: Crosstalk with Reactive Oxygen Species

Growing evidence suggests that exposure of plants to unfavorable environments leads to the accumulation of hydrogen sulfide (H2S) and reactive oxygen species (ROS). H2S interacts with the ROS-mediated oxidative stress response network at multiple levels. Therefore, it is essential to elucidate the mechanisms by which H2S and ROS interact. The molecular mechanism of action by H2S relies on the post-translational modification of the cysteine sulfur group (-SH), known as persulfidation. H2S cannot react directly with -SH, but it can react with oxidized cysteine residues, and this oxidation process is induced by H2O2. Evidently, ROS is involved in the signaling pathway of H2S and plays a significant role. In this review, we summarize the role of H2S-mediated post-translational modification mechanisms in oxidative stress responses. Moreover, the mechanism of interaction between H2S and ROS in the regulation of redox reactions is focused upon, and the positive cooperative role of H2S and ROS is elucidated. Subsequently, based on the existing evidence and clues, we propose some potential problems and new clues to be explored, which are crucial for the development of the crosstalk mechanism of H2S and ROS in plants.

cGMP functions as an important messenger involved in SlSAMS1-regulated salt stress tolerance in tomato

Salt stress adversely affects the growth, development, and yield of tomato (Solanum lycopersicum). SAM Synthetase (SAMS), which is responsible for the biosynthesis of S-adenosylmethionine (SAM, a precursor of polyamine biosynthesis), participates in plant response to abiotic stress. However, the regulatory mechanism of SAMS-mediated salt stress tolerance remains elusive. In this study, we characterized a SAMS homologue SlSAMS1 in tomato. We found that SlSAMS1 is highly expressed in tomato roots, and its expression can be induced by salt stress. Crucially, overexpression of SlSAMS1 in tomato enhances salt stress tolerance. Through metabolomic profiling, we identified some differentially accumulated metabolites, especially, a secondary messenger guanosine 3',5'-cyclic monophosphate (cGMP) which may play a key role in SlSAMS1-regulated salt tolerance. A series of physiological and biochemical data suggest that cGMP alleviates salt stress-induced growth inhibition, and potentially acts downstream of the polyamine-nitric oxide (PA-NO) signaling pathway to trigger H2O2 signaling in response to salt stress. Taken together, the study reveals that SlSAMS1 regulates tomato salt tolerance via the PA-NO-cGMP-H2O2 signal module. Our findings elucidate the regulatory pathway of SlSAMS1-induced plant response to salt stress and indicate a pivotal role of cGMP in salt tolerance.

Transcriptomic Insights into Functions of LkABCG36 and LkABCG40 in Nicotiana tabacum

ATP-binding cassette transporters (ABC transporters) play crucial physiological roles in plants, such as being involved in the growth and development of organs, nutrient acquisition, response to biotic and abiotic stress, disease resistance, and the interaction of the plant with its environment. The ABCG subfamily of proteins are involved in the process of plant vegetative organ development. In contrast, the functions of the ABCG36 and ABCG40 transporters have received considerably less attention. Here, we investigated changes in the transcriptomic data of the stem tissue of transgenic tobacco (Nicotiana tabacum) with LkABCG36 and LkABCG40 (Larix kaempferi) overexpression, and compared them with those of the wild type (WT). Compared with the WT, we identified 1120 and 318 differentially expressed genes (DEGs) in the LkABCG36 and LkABCG40 groups, respectively. We then annotated the function of the DEGs against the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The results showed enrichment in cell wall biogenesis and hormone signal transduction functional classes in transgenic LkABCG36 tobacco. In transgenic LkABCG40 tobacco, the enrichment was involved in metabolic and biosynthetic processes, mainly those related to environmental adaptation. In addition, among these DEGs, many auxin-related genes were significantly upregulated in the LkABCG36 group, and we found key genes involved in environmental adaptation in the LkABCG40 group, including an encoding resistance protein and a WRKY transcription factor. These results suggest that LkABCG36 and LkABCG40 play important roles in plant development and environmental adaptation. LkABCG36 may promote plant organ growth and development by increasing auxin transport, whereas LkABCG40 may inhibit the expression of WRKY to improve the resistance of transgenic tobacco. Our results are beneficial to researchers pursuing further study of the functions of ABCG36 and ABCG40.

Abscisic Acid Mediates Salicylic Acid Induced Chilling Tolerance of Grafted Cucumber by Activating H2O2 Biosynthesis and Accumulation

Grafting is widely applied to enhance the tolerance of some vegetables to biotic and abiotic stress. Salicylic acid (SA) is known to be involved in grafting-induced chilling tolerance in cucumber. Here, we revealed that grafting with pumpkin (Cucurbita moschata, Cm) as a rootstock improved chilling tolerance and increased the accumulation of SA, abscisic acid (ABA) and hydrogen peroxide (H₂O₂) in grafted cucumber (Cucumis sativus/Cucurbita moschata, Cs/Cm) leaves. Exogenous SA improved the chilling tolerance and increased the accumulation of ABA and H₂O₂ and the mRNA abundances of CBF1, COR47, NCED, and RBOH1. However, 2-aminoindan-2-phosphonic acid (AIP) and L-a-aminooxy-b-phenylpropionic acid (AOPP) (biosynthesis inhibitors of SA) reduced grafting-induced chilling tolerance, as well as the synthesis of ABA and H₂O₂, in cucumber leaves. ABA significantly increased endogenous H₂O₂ production and the resistance to chilling stress, as proven by the lower electrolyte leakage (EL) and chilling injury index (CI). However, application of the ABA biosynthesis inhibitors sodium tungstate (Na₂WO₄) and fluridone (Flu) abolished grafting or SA-induced H₂O₂ accumulation and chilling tolerance. SA-induced plant response to chilling stress was also eliminated by N,N'-dimethylthiourea (DMTU, an H₂O₂ scavenger). In addition, ABA-induced chilling tolerance was attenuated by DMTU and diphenyleneiodonium (DPI, an H₂O₂ inhibitor) chloride, but AIP and AOPP had little effect on the ABA-induced mitigation of chilling stress. Na₂WO₄ and Flu diminished grafting- or SA-induced H₂O₂ biosynthesis, but DMTU and DPI did not affect ABA production induced by SA under chilling stress. These results suggest that SA participated in grafting-induced chilling tolerance by stimulating the biosynthesis of ABA and H₂O₂. H₂O₂, as a downstream signaler of ABA, mediates SA-induced chilling tolerance in grafted cucumber plants.

Interactions of melatonin, reactive oxygen species, and nitric oxide during fruit ripening: an update and prospective view

Fruit ripening is a physiological process that involves a complex network of signaling molecules that act as switches to activate or deactivate certain metabolic pathways at different levels, not only by regulating gene and protein expression but also through post-translational modifications of the involved proteins. Ethylene is the distinctive molecule that regulates the ripening of fruits, which can be classified as climacteric or non-climacteric according to whether or not, respectively, they are dependent on this phytohormone. However, in recent years it has been found that other molecules with signaling potential also exert regulatory roles, not only individually but also as a result of interactions among them. These observations imply the existence of mutual and hierarchical regulations that sometimes make it difficult to identify the initial triggering event. Among these 'new' molecules, hydrogen peroxide, nitric oxide, and melatonin have been highlighted as prominent. This review provides a comprehensive outline of the relevance of these molecules in the fruit ripening process and the complex network of the known interactions among them.

Transcriptome and Physiological Analysis of Rootstock Types and Silicon Affecting Cold Tolerance of Cucumber Seedlings

Cucumbers grafted on rootstocks with different de-blooming capacity show varying levels of cold tolerance. The content of fruit bloom correlates with its silicon-metabolizing capacity, and rootstock grafting can alter not only the cold tolerance but also the silicon-metabolizing capacity of the scion. The molecular mechanisms responsible for resistance due to rootstocks and silicon and the pathway that affects cold tolerance, however, remain poorly understood. Therefore, we performed physiological and transcriptome analysis to clarify how rootstock types and silicon affect cold tolerance in cucumber seedlings. Then, we randomly selected eight differentially expressed genes (DEGs) for quantitative real time PCR (qRT-PCR) analysis to proof the reliability of the transcriptome data. The results showed that silicon can enhance the cold tolerance of cucumbers by boosting the phenylpropanoid metabolism, and rootstock grafting can boost the active oxygen scavenging ability and synthesis level of hormones in cucumbers and maintain the stability of the membrane structure to enhance cold tolerance. The difference in cold tolerance between the two rootstocks is because the cold-tolerant one has stronger metabolic and sharp signal transduction ability and can maintain the stability of photosynthesis, thereby contributing to the stability of the cellular system and enhancing tolerance to cold.