Stress response in tomato as influenced by repeated waterlogging.

Introduction: Plants respond to water stress with a variety of physiological and biochemical changes, but their response varies among species, varieties and cultivars. Waterlogging in tomato reduces plant growth, degrade chlorophyll and increase concentration of oxidative parameters. Priming can alleviate stress in plants caused by waterlogging enabling plants to be more tolerant to an additional stress in the current or even subsequent generation. The aim of this study was to evaluate tomato genotypes for their sensitivity to waterlogging stress applied during early vegetative growth and at full flowering stage. Materials and methods: The study included two local genotypes, Trebinjski sitni (GB1126) and Zuti (GB1129), and the reference variety Novosadski jabucar (NJ), which is the variety most commonly used in Serbia and Bosnia and Herzegovina. The activity of class III peroxidase (POX), hydrogen peroxide (H2O2) content and malondialdehyde (MDA) content were measured spectrophotometrically, and for quantification of individual phenolic compounds, targeted approach was adopted, using UHPLC/DAD/(-)HESI-MS2 instrument (Dionex UltiMate 3000 UHPLC system with a DAD detector, configured with a triple quadrupole mass spectrometer TSQ Quantum Access Max (Thermo Fisher Scientific, Germany)). Results and discussion: Oxidative parameters (H2O2 and MDA) exhibited an increase in content in leaves of tomato plants that underwent waterlogging stress compared to control plants. Moreover, oxidative parameters showed positive correlation with proteins and phenolics content. The obtained correlations can indicate that one of the response strategies of tomato plants to waterlogging is the increased synthesis of proteins and phenolic compounds. The POX activity was not correlated with other parameters except with the polyphenols. A positive correlation was shown between POX activity and the content of phenolic compounds, indicating their independent roles in the removal of ROS. Changes in the phenolic profiles after the exposure of plants to waterlogging stress are recorded, and these changes were more severe in leaves and fruits of GB1129 and NJ genotypes than in GB1126. Thus, genotype GB1126 is the most efficient in maintaining the phenolic profiles of leaves and fruits, and therefore of the nutritive and organoleptic qualities of fruits following the exposure to waterlogging. Also, genotype GB1126 exhibited the ability to maintain the content of oxidative parameters during waterlogging at certain growth stages, implying certain waterlogging tolerance. Conclusion: Waterlogging triggered stress memory but not at all growth stages. The most pronounced stress memory was obtained in fruit samples in the phase of full fruit maturity on the 1st truss. This study shed light on the defense mechanisms of tomato plants to repeated waterlogging stress from the perspectives of the changes in the composition of major phenolics, and pointed to the 5-O-caffeoylquinic acid and rutin as the chemical markers of the waterlogging stress tolerance in tomato. However, it remains to be determined whether this modulation has a positive or negative effect on the overall plant metabolism. Further investigations are needed to fully elucidate the benefits of waterlogging pretreatment in this context.

Patterns of Genetic Variation of Nepeta nuda L. from the Central Balkans: Understanding Drivers of Chemical Diversity.

Nepeta nuda L., a notable medicinal species in the tradition of the Balkan region, is a rich source of bioactive iridoids and phenolics previously described as high-resolution taxonomical classifiers for the genus Nepeta. However, their potential in investigating intra-species differentiation is here described for the first time. The aim was to recognize the sources of natural chemical diversity and their association with the genetic variability both within and among N. nuda populations in the Central Balkans. Chemical diversity was assessed from methanol extracts and essential oils through untargeted and targeted metabolomics using state-of-the-art analytical tools, covering a broad spectrum of compounds that represent the N. nuda metabolome. We found that chemodiversity primarily resides within populations of N. nuda, and similar results were obtained at the DNA level using microsatellite markers. The low genetic and chemical differentiation of the studied N. nuda populations implies that their metabolomic profiles may be less influenced by geographic distance and variable environmental conditions within the Central Balkans, as they are under the pivotal control of their genetic backgrounds. Screening the distribution of the major bioactive compounds belonging to phenolics (phenolic acids and flavonoids) and iridoids (both aglycones and glycosylated forms), within and among N. nuda populations, is able to guarantee mass spectrometry-based tools for the selection of elite representative genotypes with practical importance. The knowledge acquired will allow us to delve deeper into the molecular background of N. nuda chemical diversity, which is the course of our further work.

Cytokinins enhance the metabolic activity of in vitro-grown catmint (Nepeta nuda L.).

The phytohormones cytokinins are essential mediators of developmental and environmental signaling, primarily during cell division and endophytic interactions, among other processes. Considering the limited understanding of the regulatory mechanisms that affect the growth and bioactivity of the medicinal plant Nepeta nuda (Lamiaceae), our study aimed to explore how cytokinins influence the plant's metabolic status. Exogenous administration of active cytokinin forms on in vitro N. nuda internodes stimulated intensive callus formation and de novo shoot regeneration, leading to a marked increase in biomass. This process involved an accumulation of oxidants, which were scavenged by peroxidases using phenolics as substrates. The callus tissue formed upon the addition of the cytokinin 6-benzylaminopurine (BAP) acted as a sink for sugars and phenolics during the allocation of nutrients between the culture medium and regenerated plants. In accordance, the cytokinin significantly enhanced the content of polar metabolites and their respective in vitro biological activities compared to untreated in vitro and wild-grown plants. The BAP-mediated accumulation of major phenolic metabolites, rosmarinic acid (RA) and caffeic acid (CA), corresponded with variations in the expression levels of genes involved in their biosynthesis. In contrast, the accumulation of iridoids and the expression of corresponding biosynthetic genes were not significantly affected. In conclusion, our study elucidated the mechanism of cytokinin action in N. nuda in vitro culture and demonstrated its potential in stimulating the production of bioactive compounds. This knowledge could serve as a basis for further investigations of the environmental impact on plant productivity.

Functional iridoid synthases from iridoid producing and non-producing Nepeta species (subfam. Nepetoidae, fam. Lamiaceae).

Iridoids, a class of atypical monoterpenes, exhibit exceptional diversity within the Nepeta genus (subfam. Nepetoidae, fam. Lamiaceae).The majority of these plants produce iridoids of the unique stereochemistry, with nepetalactones (NLs) predominating; however, a few Nepeta species lack these compounds. By comparatively analyzing metabolomics, transcriptomics, gene co-expression, and phylogenetic data of the iridoid-producing N. rtanjensis Diklic & Milojevic and iridoid-lacking N. nervosa Royle & Bentham, we presumed that one of the factors responsible for the absence of these compounds in N. nervosa is iridoid synthase (ISY). Two orthologues of ISY were mined from leaves transcriptome of N. rtanjensis (NrPRISE1 and NrPRISE2), while in N. nervosa only one (NnPRISE) was identified, and it was phylogenetically closer to the representatives of the Family 1 isoforms, designated as P5ßRs. Organ-specific and MeJA-elicited profiling of iridoid content and co-expression analysis of IBG candidates, highlighted NrPRISE2 and NnPRISE as promising candidates for ISY orthologues, and their function was confirmed using in vitro assays with recombinant proteins, after heterologous expression of recombinant proteins in E. coli and their His-tag affinity purification. NrPRISE2 demonstrated ISY activity both in vitro and likely in planta, which was supported by the 3D modeling and molecular docking analysis, thus reclassification of NrPRISE2 to NrISY is accordingly recommended. NnPRISE also displays in vitro ISY-like activity, while its role under in vivo conditions was not here unambiguously confirmed. Most probably under in vivo conditions the NnPRISE lacks substrates to act upon, as a result of the loss of function of some of the upstream enzymes of the iridoid pathway. Our ongoing work is conducted towards re-establishing the biosynthesis of iridoids in N. nervosa.