Efficacy of ABA-Mimicking Ligands in Controlling Water Loss and Maintaining Antioxidative Capacity of Spinacia oleracea

Melatonin extends shelf life in postharvest okra via delaying fruit softening and reducing weight loss

BACKGROUND

Melatonin, a hormone present in animals and some plants, has garnered attention for its potential in preserving harvested produce. Softening due to changes in cell wall composition and wilting caused by weight loss are the major reasons for the loss of commercial value in postharvest okra. This study aimed to evaluate the impact of melatonin on the softening and weight loss of postharvest okra.

RESULTS

The results revealed that the application of melatonin had a significant influence on the maintenance of fruit firmness by inhibiting the breakdown and dissolution of cell wall polysaccharides by suppressing the expression of specific genes responsible for cell wall degradation in okra. Conversely, melatonin treatment positively influenced the expression of genes involved in the synthesis of cell wall components. Furthermore, the treatment exhibited notable benefits in reducing weight loss in okra, which was accomplished by promoting the closure of stomata - the tiny pores on the surface of the fruit.

CONCLUSION

Melatonin could serve as a novel approach to reduce water loss, delay fruit softening and extend the shelf life of okra. © 2024 Society of Chemical Industry.

LcASR enhances tolerance to abiotic stress in Leymus chinensis and Arabidopsis thaliana by improving photosynthetic performance

As a crucial forage grass, Leymus chinensis plays significant roles in soil and water conservation owing to its robust stress resistance. However, the underlying molecular mechanisms of its stress tolerance remain unclear. In this study, a novel gene, designated as LcASR (Abiotic Stress Resistance in Leymus chinensis), imparting resilience to both high light and drought, was identified. Under normal growth conditions, heterologous overexpression of LcASR in Arabidopsis (HO lines) showed no significant difference in appearance compared to wild-type. Nevertheless, HO lines accumulate significantly higher chlorophyll content during the dark-to-light transition compared to the wild-type, indicating that the LcASR protein participates in chlorophyll synthesis during chloroplast development. Meanwhile, transgenic Arabidopsis and L. chinensis plants exhibited resistance to abiotic stresses such as high light and drought. Photosystem complexes analysis revealed that LHCII proteins remained stable within their respective complexes during high light stress. We hypothesize that LcASR may play a role in fine tuning of chlorophyll synthesis to enable plant adaptation to diverse stress conditions. Moreover, overexpression of LcASR in L. chinensis led to agronomically valuable traits such as deeper green color, higher biomass accumulation, prolonged withering period, and extended grazing durations. This study uncovers a novel gene in L. chinensis that enhances forage yield and provides valuable genetic resources for sheepgrass breeding.

Abscisic acid mimic-fluorine derivative 4 alleviates water deficit stress by regulating ABA-responsive genes, proline accumulation, CO2 assimilation, water use efficiency and better nutrient uptake in tomato plants

Water deficit represents a serious limitation for agriculture and both genetic and chemical approaches are being used to cope with this stress and maintain plant yield. Next-generation agrochemicals that control stomatal aperture are promising for controlling water use efficiency. For example, chemical control of abscisic acid (ABA) signaling through ABA-receptor agonists is a powerful method to activate plant adaptation to water deficit. Such agonists are molecules able to bind and activate ABA receptors and, although their development has experienced significant advances in the last decade, few translational studies have been performed in crops. Here, we describe protection by the ABA mimic-fluorine derivative 4 (AMF4) agonist of the vegetative growth in tomato plants subjected to water restriction. Photosynthesis in mock-treated plants is markedly impaired under water deficit conditions, whereas AMF4 treatment notably improves CO₂ assimilation, the relative plant water content and growth. As expected for an antitranspirant molecule, AMF4 treatment diminishes stomatal conductance and transpiration in the first phase of the experiment; however, when photosynthesis declines in mock-treated plants as stress persists, higher photosynthetic and transpiration parameters are recorded in agonist-treated plants. Additionally, AMF4 increases proline levels over those achieved in mock-treated plants in response to water deficit. Thus water deficit and AMF4 cooperate to upregulate P5CS1 through both ABA-independent and ABA-dependent pathways, and therefore, higher proline levels are produced Finally, analysis of macronutrients reveals higher levels of Ca, K and Mg in AMF4- compared to mock-treated plants subjected to water deficit. Overall, these physiological analyses reveal a protective effect of AMF4 over photosynthesis under water deficit and enhanced water use efficiency after agonist treatment. In summary, AMF4 treatment is a promising approach for farmers to protect the vegetative growth of tomatoes under water deficit stress.

Functional characterization of wild soybean (Glycine soja) GsSnRK1.1 protein kinase in plant resistance to abiotic stresses

Protein kinases play crucial roles in the regulation of plant resistance to various stresses. In this work, we determined that GsSnRK1.1 was actively responsive to saline-alkali, drought, and abscisic acid (ABA) stresses by histochemical staining and qRT-PCR analyses. The wild-type GsSnRK1.1 but not the kinase-dead mutant, GsSnRK1.1(K49M), demonstrated in vitro kinase activity by phosphorylating GsABF2. Intriguingly, we found that GsSnRK1.1 could complement the loss of SNF1 kinase in yeast Msy1193 (-snf1) mutant, rescue growth defects of yeast cells on medium with glycerol as a carbon resource, and promote yeast resistance to NaCl or NaHCO₃. To further elucidate GsSnRK1.1 function in planta, we knocked out SnRK1.1 gene from the Arabidopsis genome by the CRISPR/Cas9 approach, and then expressed GsSnRK1.1 and a series of mutants into snrk1.1-null lines. The transgenic Arabidopsis lines were subjected to various abiotic stress treatments. The results showed that GsSnRK1.1(T176E) mutant with enhanced protein kinase activity significantly promoted, but GsSnRK1.1(K49M) and GsSnRK1.1(T176A) mutants with disrupted protein kinase activity abrogated, plant stomatal closure and tolerance to abiotic stresses. In conclusion, this study provides the molecular clues to fully understand the physiological functions of plant SnRK1 protein kinases.

Melatonin Preserves the Postharvest Quality of Cut Roses through Enhancing the Antioxidant System

The vase life of cut rose is relatively short, therefore; preserving its postharvest quality via eco-friendly approaches is of particular economic importance. From the previous literature, despite melatonin (MT) plays diverse important roles in the postharvest quality maintenance, its impact on preserving the postharvest quality of cut flowers is really scarce. This research therefore was undertaken to find out the possibility of exogenous MT as an eco-friendly preservative to extend the vase life of cut roses. The flowering stems of Rosa hybrida cv. 'First Red' were pulsed in MT solutions at 0, 0.1, 0.2 and 0.3 mM for 30 min and then transferred to distilled water for evaluation. The vase life was significantly prolonged and relative water content was considerably maintained due to MT application compared to the control, more so with 0.2 mM concentration which nearly doubled the vase life (1.9-fold) higher than the control. SEM investigation showed that MT treatment reduced the stomatal aperture in lower epidermis which was widely opened in control flowers. MT treatment significantly increased the phenol content, glutathione (GSH) content and CAT, APX and GR enzyme activities compared to untreated flowers. Additionally, the radical scavenging capacity in MT-treated flowers was considerably higher than that of control and therefore MT treatment reduced H₂O₂ production and lipid peroxidation, which altogether reflected in membrane stability maintenance.

Abscisic Acid Signaling in the Regulation of Postharvest Physiological Deterioration of Sliced Cassava Tuberous Roots

Phytohormone abscisic acid (ABA) influences the shelf life of fruit, vegetables, and tubers after harvest. However, little is known about the core signaling module involved in ABA's control of the postharvest physiological process. Exogenous ABA alleviated postharvest physiological deterioration (PPD) symptoms of sliced cassava tuberous roots, increased endogenous ABA levels, and reduced endogenous H₂O₂ content. The specific ABA signaling module during the PPD process was identified as MePYL6-MePP2C16-MeSnRK2.1-MebZIP5/34. MebZIP5/MebZIP34 directly binds to and activates the promoters of MeGRX6/MeMDAR1 through ABRE elements. Exogenous ABA significantly induced the expression of genes involved in this module, glutaredoxin content, and monodehydroascorbate reductase activity. We presented a hypothesis suggesting that MePYL6-MePP2C16-MeSnRK2.1-MebZIP5/34-MeGRX6/MeMDAR1 is involved in ABA-induced antioxidative capacity, thus alleviating PPD symptoms in cassava tuberous roots. The identification of the specific signaling module involved in ABA's control of PPD provides a basis and potential targets for extending the shelf life of cassava tuberous roots.

Pretreatment with high oxygen controlled atmosphere enhanced fresh-cut white mushroom (Agaricus bisporus) quality via activating wounding stress defenses

BACKGROUND

High oxygen treatment has been proven to be effective in fresh-cut white mushroom preservation, however, the preservation effect and possible mechanisms in high oxygen controlled atmosphere pretreatment (HOCAP) on wounding stress are incompletely understood.

RESULTS

In this study, based on the time chosen of HOCAP research, whole white mushrooms treated with 3 h HOCAP (80% O₂  + 20% CO₂ ) and the wounding resistant responses of their slices were mainly investigated through phenylpropane pathway, reactive oxygen species (ROS) scavenging system, and ascorbate-glutathione (AsA-GSH) cycle. Results showed that 3 h HOCAP can induce the production of hydrogen peroxide (H₂ O₂ ) and superoxide anion (O₂ ^-• ) in the early stage, as well as the NADPH oxidase activity. Enzymes and endogenous antioxidants involved in ROS scavenging were enhanced by HOCAP during the whole storage. Besides, HOCAP maintained high level of phenylalanine ammonia-lyase (PAL) activity, enhanced the content of total phenolic and lignin, accelerated the AsA-GSH cycle.

CONCLUSION

The results demonstrated that HOCAP induced defense responses by increasing the ROS in the early stage which stimulated the activities of ROS scavenging enzymes, along with the capability of increasing for wounding stress defense and resistance. This study provides a theoretical pretreatment technology for fresh-cut white mushroom preservation. © 2021 Society of Chemical Industry.

PdeHCA2 affects biomass in Populus by regulating plant architecture, the transition from primary to secondary growth, and photosynthesis

PdeHCA2 regulates the transition from primary to secondary growth, plant architecture, and affects photosynthesis by targeting PdeBRC1 and controlling the anatomy of the mesophyll, and intercellular space, respectively. Branching, secondary growth, and photosynthesis are vital developmental processes of woody plants that determine plant architecture and timber yield. However, the mechanisms underlying these processes are unknown. Here, we report that the Populus transcription factor High Cambium Activity 2 (PdeHCA2) plays a role in the transition from primary to secondary growth, vascular development, and branching. In Populus, PdeHCA2 is expressed in undifferentiated provascular cells during primary growth, in phloem cells during secondary growth, and in leaf veins, which is different from the expression pattern of its homolog in Arabidopsis. Overexpression of PdeHCA2 has pleiotropic effects on shoot and leaf development; overexpression lines showed delayed growth of shoots and leaves, reduced photosynthesis, and abnormal shoot branching. In addition, auxin-, cytokinin-, and photosynthesis-related genes were differentially regulated in these lines. Electrophoretic mobility shift assays and transcriptome analysis indicated that PdeHCA2 directly up-regulates the expression of BRANCHED1 and the MADS-box gene PdeAGL9, which regulate plant architecture, by binding to cis-elements in the promoters of these genes. Taken together, our findings suggest that HCA2 regulates several processes in woody plants including vascular development, photosynthesis, and branching by affecting the proliferation and differentiation of parenchyma cells.

Characterization of a short-chain dehydrogenase/reductase and its function in patulin biodegradation in apple juice

Biodegradation based on microbial enzymes is considered to be one of the promising ways for controlling patulin contamination. However, few patulin degrading enzymes have been isolated and characterized until now. Here, a short-chain dehydrogenase/reductase (SDR) gene, CgSDR, was cloned from a yeast strain Candida guilliermondii, and expressed in Escherichia coli. The expression of CgSDR conferred a strong patulin tolerance and degradation ability to E. coli, and purified CgSDR could transform patulin into E-ascladiol in vitro with NADPH as a coenzyme. Moreover, addition of CgSDR at 150 μg/mL could reduce 80% of patulin in apple juice and the biodegradation process did not affect the quality of the apple juice. A molecular docking analysis and site-directed mutagenesis indicated that CgSDR might interact with patulin via VAL188 as an active binding sites. The findings provide new insights for developing enzymic formulations for mycotoxin detoxification in fruit derived products.

Melatonin delays leaf senescence of postharvest Chinese flowering cabbage through ROS homeostasis

Reactive oxygen species (ROS) trigger and accelerate leaf senescence. Melatonin, a low molecular compound with several biological functions in plants, is known to delay leaf senescence in different species, including Chinese flowering cabbage. However, the mechanism(s) underpinning melatonin-delayed leaf senescence remains unclear. Here, we found that melatonin lowered the expression of chlorophyll catabolic genes (BrPAO and BrSGR1) and senescence-associated genes (BrSAG12 and BrSEN4), decreased chlorophyll loss, minimized the alteration in Fv/Fm ratio and remarkably delayed senescence of Chinese flowering cabbage after harvest. Moreover, the over-accumulation of O₂^•-, hydrogen peroxide (H₂O₂) and malondialdehyde contents and the expression of respiratory burst oxidase homologues (RBOH) genes (BrRbohB, BrRbohC, BrRbohD, BrRbohD2 and BrRbohE) were significantly inhibited by melatonin treatment. Melatonin-treated cabbages also showed higher O₂^•-, OH^• and DPPH radical scavenging capacity and enhanced activities of peroxidase (POD), superoxide dismutase (SOD) and their gene expressions. Up-regulation of key components of ascorbate-glutathione (AsA-GSH) cycle, the metabolic pathway that detoxify H₂O₂, was also observed in melatonin-treated cabbages. These findings suggest that melatonin-delayed postharvest leaf senescence of postharvest Chinese flowering cabbage may be mediated, at least in part, by maintaining ROS homeostasis through restraining RBOHs-catalyzed ROS production and enhancing the activity of ROS-scavenging system including major antioxidant enzymes and AsA-GSH cycle.

Agonist, antagonist and signaling modulators of ABA receptor for agronomic and post-harvest management

Abscisic acid (ABA) is a ubiquitous phytohormone, plays important roles in several physiological processes, including stress adaptation, flowering, seed germination, fruit ripening, and leaf senescence etc. ABA binds with START domain proteins called Pyrabactin Resistance1 (PYR1)/PYR1-like (PYL)/Regulatory Components of ABA Receptors (RCARs) and controls the activity of PP2C phosphatase proteins and in turn the ABA-dependent signaling pathway. Fourteen ABA receptors have been identified in the model plant Arabidopsis thaliana and have shown to be involved in various biological functions. Under field conditions, exogenous application of ABA produces inadequate physiological response due to its rapid conversion into the biologically inactive metabolites. ABA shows selective binding preferences to PYL receptor subtypes and hence produces pleiotropic physiological and phenotypic effects which limit the usage of ABA in agriculture. An agrochemical meant for ameliorating the undesirable physiological effect of the plant should ideally have positive biological attributes without affecting the normal growth, development, and yield. Therefore, to overcome the limitations of ABA for its usage in various agricultural applications, several types of ABA-mimicking agents have been developed. Many compounds have been identified as having significant ABA-agonist/antagonist activity and can be employed to reverse the excessive/moderate ABA action. The present review highlights the potential usage of ABA signaling modulators for managing agronomic and postharvest traits. Besides, designing, development and versatile usage of ABA-mimicking compounds displaying ABA agonists and antagonist activities are discussed in detail.

Role of the Ring Methyl Groups in 2',3'-Benzoabscisic Acid Analogues

Five analogues of iso-PhABA (20) developed earlier by our research group were designed and synthesized. The bioassay results show that the number and position of methyl groups along with the substitution of hydrogen atoms of the methyl group have a great influence on the activity. Compared with iso-PhABA, the inhibitory activity of diMe-PhABA (21) on seed germination and rice seedling growth decreased slightly; however, it significantly reduced the capability of inhibiting wheat embryo germination. Both 3'-deMe- iso-PhABA (22) and 2'-deMe-PhABA (23) exhibited weak inhibitory activities, and 11'-methoxy iso-PhABA (24a/24b) was much more efficient than its isomer 24c/24d in all bioassays. These results reveal the preservation of quaternary carbon at the 2' or 3' position is necessary to maintain its ABA-like biological activity, and demethylation at the 3' position has a more significant effect. The selectivity of these compounds to different physiological processes makes them available as selective probes for different ABA receptors.