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High-throughput profiling of key enzyme activities of carbon, nitrogen, and antioxidant metabolism is emerging as a valuable approach to integrate cell physiological phenotyping into a holistic functional phenomics approach. However, the analyses of the large datasets generated by this method represent a bottleneck, often keeping researchers from exploiting the full potential of their studies. We address these limitations through the exemplary application of a set of data evaluation and visualisation tools within a case study. This includes the introduction of multivariate statistical analyses which can easily be implemented in similar studies, allowing researchers to extract more valuable information to identify enzymatic biosignatures. Through a literature meta-analysis, we demonstrate how enzyme activity profiling has already provided functional information on the mechanisms regulating plant development and response mechanisms to abiotic stress and pathogen attack. The high robustness of the distinct enzymatic biosignatures observed during developmental processes and under stress conditions underpins the enormous potential of enzyme activity profiling for future applications both in basic and applied research. Enzyme activity profiling will complement molecular -omics approaches to contribute to the mechanistic understanding required to narrow the genotype-to-phenotype knowledge gap and to identify predictive biomarkers for plant breeding to develop climate-resilient crops.

Agriculture has always been the most susceptible sector to climate change, as environmental stresses severely impact plant development and final yield. The interest in the application of plant growth promoting rhizobacteria (PGPR) in agriculture is exponentially increasing, as it provides a sustainable solution against hazardous agrochemicals. A vast amount of research has indicated that PGPRs can have bio stimulatory activity and function as biocontrol agents, providing protection against biotic and abiotic stresses and therefore offering a less environmentally invasive approach to food supply. This study was conducted to enlighten the effects of two PGPRs, the Enterobacter spp., and the commercially applied Bacillus amyloliquefaciens FZB42, on root growth and architecture as well as on carbohydrate-metabolic and antioxidant enzyme activity in barley (Hordeum vulgare cv Guld). Preliminary experimental results have shown that the impact of Enterobacter spp. is very similar to the effect of cytokinins on root growth. The bacterial inoculation response of the plants was initially characterized by phenotypical and biochemical analysis. There was no distinct effect on the root system and plant metabolism with FZB42 treatment, therefore further focus was given only to the impact of Enterobacter spp. Enterobacter spp. caused a strong inhibitory impact on root growth and affected the carbohydrate and antioxidant enzyme activity of plants grown in vitro. This specific effect on roots did not appear under soil conditions, in greenhouse experiments. The study around Enterobacter spp. was complemented with analysis of the available RNA Sequencing data. Expression profiling of the roots of barley plants identified the number of differentially regulated genes. Functional annotation of these differentially expressed genes was performed using Gene Ontology (GO) and the Kyoto Encyclopedia

It has been recognized that cytokinins are plant hormones that influence not only numerous aspects of plant growth, development and physiology, including cell division, chloroplast differentiation and delay of senescence but the interaction with other organisms, including pathogens. Cytokinins are not only produced by plants but are also by other prokaryotic and eukaryotic organism such as bacteria, fungi, microalgae and insects. Notably, cytokinins are produced both by pathogenic and also beneficial microbes and are known to induce resistance in plants against pathogen infections. In this review the contrasting role of cytokinin for the defence and susceptibility of plants against bacterial and fungal pathogen and pest insects is assessed. We also discuss the cross talk of cytokinins with other phytohormones and the underlying mechanism involved in enhancing plant immunity against pathogen infections and explore possible practical applications in crop plant production.

Plant–pathogen interactions have been widely studied, but mostly from the site of the plant secondary defense. Less is known about the effects of pathogen infection on plant primary metabolism. The possibility to transform a fluorescing protein into prokaryotes is a promising phenotyping tool to follow a bacterial infection in plants in a noninvasive manner. In the present study, virulent and avirulent Pseudomonas syringae strains were transformed with green fluorescent protein (GFP) to follow the spread of bacteria in vivo by imaging Pulse-Amplitude-Modulation (PAM) fluorescence and conventional binocular microscopy. The combination of various wavelengths and filters allowed simultaneous detection of GFP-transformed bacteria, PAM chlorophyll fluorescence, and phenolic fluorescence from pathogen-infected plant leaves. The results show that fluorescence imaging allows spatiotemporal monitoring of pathogen spread as well as phenolic and chlorophyll fluorescence in situ, thus providing a novel means to study complex plant–pathogen interactions and relate the responses of primary and secondary metabolism to pathogen spread and multiplication. The study establishes a deeper understanding of imaging data and their implementation into disease screening.