THROUGH THE LOOKING GLASS: Real-Time Imaging in Brachypodium Roots and Osmotic Stress Analysis

Microfluidics-Based Bioassays and Imaging of Plant Cells

Many plant processes occur in the context of and in interaction with a surrounding matrix such as soil (e.g. root growth and root-microbe interactions) or surrounding tissues (e.g. pollen tube growth through the pistil), making it difficult to study them with high-resolution optical microscopy. Over the past decade, microfabrication techniques have been developed to produce experimental systems that allow researchers to examine cell behavior in microstructured environments that mimic geometrical, physical and/or chemical aspects of the natural growth matrices and that cannot be generated using traditional agar plate assays. These microfabricated environments offer considerable design flexibility as well as the transparency required for high-resolution, light-based microscopy. In addition, microfluidic platforms have been used for various types of bioassays, including cellular force assays, chemoattraction assays and electrotropism assays. Here, we review the recent use of microfluidic devices to study plant cells and organs, including plant roots, root hairs, moss protonemata and pollen tubes. The increasing adoption of microfabrication techniques by the plant science community may transform our approaches to investigating how individual plant cells sense and respond to changes in the physical and chemical environment.

Designs, applications, and limitations of genetically encoded fluorescent sensors to explore plant biology

The understanding of signaling and metabolic processes in multicellular organisms requires knowledge of the spatial dynamics of small molecules and the activities of enzymes, transporters, and other proteins in vivo, as well as biophysical parameters inside cells and across tissues. The cellular distribution of receptors, ligands, and activation state must be integrated with information about the cellular distribution of metabolites in relation to metabolic fluxes and signaling dynamics in order to achieve the promise of in vivo biochemistry. Genetically encoded sensors are engineered fluorescent proteins that have been developed for a wide range of small molecules, such as ions and metabolites, or to report biophysical processes, such as transmembrane voltage or tension. First steps have been taken to monitor the activity of transporters in vivo. Advancements in imaging technologies and specimen handling and stimulation have enabled researchers in plant sciences to implement sensor technologies in intact plants. Here, we provide a brief history of the development of genetically encoded sensors and an overview of the types of sensors available for quantifying and visualizing ion and metabolite distribution and dynamics. We further discuss the pros and cons of specific sensor designs, imaging systems, and sample manipulations, provide advice on the choice of technology, and give an outlook into future developments.

Specialized Plant Growth Chamber Designs to Study Complex Rhizosphere Interactions

The rhizosphere is a dynamic ecosystem shaped by complex interactions between plant roots, soil, microbial communities and other micro- and macro-fauna. Although studied for decades, critical gaps exist in the study of plant roots, the rhizosphere microbiome and the soil system surrounding roots, partly due to the challenges associated with measuring and parsing these spatiotemporal interactions in complex heterogeneous systems such as soil. To overcome the challenges associated with in situ study of rhizosphere interactions, specialized plant growth chamber systems have been developed that mimic the natural growth environment. This review discusses the currently available lab-based systems ranging from widely known rhizotrons to other emerging devices designed to allow continuous monitoring and non-destructive sampling of the rhizosphere ecosystems in real-time throughout the developmental stages of a plant. We categorize them based on the major rhizosphere processes it addresses and identify their unique challenges as well as advantages. We find that while some design elements are shared among different systems (e.g., size exclusion membranes), most of the systems are bespoke and speaks to the intricacies and specialization involved in unraveling the details of rhizosphere processes. We also discuss what we describe as the next generation of growth chamber employing the latest technology as well as the current barriers they face. We conclude with a perspective on the current knowledge gaps in the rhizosphere which can be filled by innovative chamber designs.

Analysis of Aldo-Keto Reductase Gene Family and Their Responses to Salt, Drought, and Abscisic Acid Stresses in Medicago truncatula

Salt and drought stresses are two primary abiotic stresses that inhibit growth and reduce the activity of photosynthetic apparatus in plants. Abscisic acid (ABA) plays a key role in abiotic stress regulation in plants. Some aldo-keto reductases (AKRs) can enhance various abiotic stresses resistance by scavenging cytotoxic aldehydes in some plants. However, there are few comprehensive reports of plant AKR genes and their expression patterns in response to abiotic stresses. In this study, we identified 30 putative AKR genes from Medicago truncatula. The gene characteristics, coding protein motifs, and expression patterns of these MtAKRs were analyzed to explore and identify candidate genes in regulation of salt, drought, and ABA stresses. The phylogenetic analysis result indicated that the 52 AKRs in Medicago truncatula and Arabidopsis thaliana can be divided into three groups and six subgroups. Fifteen AKR genes in M. truncatula were randomly selected from each group or subgroup, to investigate their response to salt (200 mM of NaCl), drought (50 g·L^-1 of PEG 6000), and ABA (100 µM) stresses in both leaves and roots. The results suggest that MtAKR1, MtAKR5, MtAKR11, MtAKR14, MtAKR20, and MtAKR29 may play important roles in response to these stresses.