Plant Science

Murashige-Skoog medium solutions have been used in a variety of plant plate growth assays, yet most research uses Arabidopsis thaliana as the study organism. For larger seeds such as maize (Zea mays), most protocols employ a paper towel roll method for experiments, which often involves wrapping maize seedlings in wet, sterile germination paper. What the paper towel roll method lacks, however, is the ability to image the roots over time without risk of contamination. Here, we describe a sterile plate growth assay that contains Murashige-Skoog medium to grow seedlings starting two days after germination. This protocol uses a section of a paper towel roll method to achieve uniform germination of maize seedlings, which are sterilely transferred onto large acrylic plates for the duration of the experiment. The media can undergo modification to include an assortment of plant hormones, exogenous sugars, and other chemicals. The acrylic plates allow researchers to freely image the plate without disturbing the seedlings and control the environment in which the seedlings are grown, such as modifications in temperature and light. Additionally, the protocol is widely adaptable for use with other cereal crops.

Key features

• Builds upon plate growth methods routinely used for Arabidopsis seedlings but that are inadequate for maize.

• Real-time photographic analysis of seedlings up to two weeks following germination.

• Allows for testing of various growth conditions involving an assortment of additives and/or modification of environmental conditions.

• Samples are able to be collected for genotype screening.

Graphical overview

The chloroplast lumen contains at least 80 proteins whose function and regulation are not yet fully understood. Isolating the chloroplast lumen enables the characterization of the lumenal proteins. The lumen can be isolated in several ways through thylakoid disruption using a Yeda press or sonication, or through thylakoid solubilization using a detergent. Here, we present a simple procedure to isolate thylakoid lumen by sonication using leaves of the plant Arabidopsis thaliana. The step-by-step procedure is as follows: thylakoids are isolated from chloroplasts, loosely associated thylakoid surface proteins from the stroma are removed, and the lumen fraction is collected in the supernatant following sonication and centrifugation. Compared to other procedures, this method is easy to implement and saves time, plant material, and cost. Lumenal proteins are obtained in high quantity and purity; however, some stromal membrane–associated proteins are released to the lumen fraction, so this method could be further adapted if needed by decreasing sonication power and/or time.

Paraquat is a cost-effective herbicide, widely used in many countries, that can induce severe oxidative stress in photosynthetic tissues. Studying plant herbicide resistance or antioxidant stress mechanisms requires determining the cellular paraquat level when plants are treated by paraquat. The traditional isotopic labeling method has the potential risk to cause problems to both human health and the environment. For radioisotope manipulation, special operation spaces and strict environmental inspection are also required. In addition, the radiolabeled paraquat is increasingly hard to buy due to the extended production cycle. Here, we describe a nonradioactive method to determine the paraquat level in a small number of Arabidopsis tissues or protoplasts, using a high resolution ultra-high-performance liquid chromatography (UHPLC)-mass spectrometry (MS)/MS method. This method is highly selective and sensitive, and more environmentally compatible and technically feasible than the isotope detection method.

Identifying genetic variations or treatments that confer greater resistance to drought is paramount to ensuring sustainable crop productivity. Accurate and reproducible measurement of drought stress symptoms can be achieved via automated, image-based phenotyping. Many phenotyping platforms are either cost-prohibitive, require specific technical expertise, or are simply more complex than necessary to effectively evaluate drought resistance. Certain mutations, allelic variations, or treatments result in plants that constitutively use less water. To accurately identify genetic differences or treatments that confer a drought phenotype, plants from all experimental groups must be subjected to equal levels of drought stress. This can be easily achieved by growing and imaging plants that are grown in the same pot. Here, we provide a detailed protocol to configure a Raspberry Pi computer and camera module to image seedlings of multiple genotypes growing in shared pots and to transfer images and metadata via the cloud for downstream analyses. Also detailed is a method to calculate percent soil water content of pots while being imaged to allow for comparison of stress symptoms with water availability. This protocol was recently used to uncouple differential water usage from drought resistance in a dwarf Arabidopsis thaliana mutant chiquita1-1/cost1 compared to the wild-type control. It is cost effective, suitable for any plant species, customizable to various biological questions, and requires no prior experience with electronics or basic software programming.

The ascorbate peroxidase (APX) is a widely distributed antioxidant enzyme. It differs from catalase and other peroxidases in that it scavenges/reduces reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) to water using reduced ascorbate as the electron donor. It is advantageous over other similar antioxidant enzymes in scavenging ROS since ascorbate may react with superoxide, singlet oxygen, and hydroxyl radical, in addition to reacting with H₂O₂. The estimation of its activity is helpful to analyze the level of oxidative stress in living systems under stressful conditions. The present protocol was performed to analyze the impact of heavy metal chromium (Cr) toxicity on sorghum plants in the form of APX enzyme activity under the application of glycine betaine (GB) and arbuscular mycorrhizal fungi (AMF) as stress ameliorators. Plant defense strategies against heavy metals toxicity involve the utilization of APX and the instigation of AMF symbiotic system, as well as their possible collaboration with one another or with the plant antioxidant system; this has been examined and discussed in literature. In this protocol, an increased APX activity was observed on underlying functions and detoxification capabilities of GB and AMF that are typically used by plants to enhance tolerance to Cr toxicity.

Graphical abstract:

Flow chart of standardized or calibrated enzyme assay with leaf samples of sorghum

Nicotinamide adenine dinucleotide (NAD) is an essential cofactor of numerous enzymatic reactions found in all living cells. Pyridine nucleotides (NAD⁺ and NADH) are also key players in signaling through reactive oxygen species (ROS), being crucial in the regulation of both ROS-producing and ROS-consuming systems in plants. NAD content is a powerful modulator of metabolic integration, protein de-acetylation, and DNA repair. The balance between NAD oxidized and reduced forms, i.e., the NADH/NAD⁺ ratio, indicates the redox state of a cell, and it is a measurement that reflects the metabolic health of cells. Here we present an easy method to estimate the NAD⁺ and NADH content enzymatically, using alcohol dehydrogenase (ADH), an oxido-reductase enzyme, and with MTT (3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) as the substrate and 1-methoxy PMS (1-Methoxy-5-methylphenazinium methyl sulfate) as the electron carrier. MTT is reduced to a purple formazan, which is then detected. We used Arabidopsis leaf samples exposed to aluminum toxicity and under untreated control conditions. NADH/NAD⁺ connects many aspects of metabolism and plays vital roles in plant developmental processes and stress responses. Therefore, it is fundamental to determine the status of NADH/NAD⁺ under stress.

Embolism, the formation of air bubbles in the plant water transport system, has a major impact on plant water relations. Embolism formation in the water transport system of plants disrupts plant water transport capacity, impairing plant functioning and triggering plant mortality. Measuring embolism with traditional hydraulic methods is both time-consuming and requires large amounts of plant material. While the stem hydraulic methods measure loss of xylem hydraulic conductance due to embolism formation, the pneumatic method directly quantifies the amount of emboli inside the xylem as changes in xylem air content. The pneumatic method is an easy and fast (8+ embolism curves per day) method to measure plant embolism requiring minimal plant material. Here, we provide detailed descriptions and recent technical improvements on the pneumatic method.

Cell membrane prevents the entrance of extra molecules (e.g., transcription and translation inhibitors) into the cell. For studying the physiological effects of transcription and translation inhibitors on Hymenophyllum caudiculatum fronds, we incubate fronds with 0.1% DMSO to test if this increases cell membrane permeability relative to incubation with ultrapure water. The study showed that DMSO could significantly improve the cell membrane permeability of filmy fronds.

Filmy ferns can desiccate and recover after rehydration to resume photosynthesis. Slow and fast desiccation rates were compared in filmy fern fronds to determine whether structural or physiological differences may occur between desiccation rates. Slow desiccation is considered to be more similar to natural conditions experienced by plants that grow under the forest canopy. A fast desiccation rate will help to understand whether slow desiccation is important for recovery and viability.

High-throughput phenotyping of plant traits is a powerful tool to further our understanding of plant growth and its underlying physiological, molecular, and genetic determinisms. This protocol describes the methodology of a standard phenotyping experiment in PHENOPSIS automated platform, which was engineered in INRA-LEPSE (https://www6.montpellier.inra.fr/lepse) and custom-made by Optimalog company. The seminal method was published by Granier et al. (2006). The platform is used to explore and test various ecophysiological hypotheses (Tisné et al., 2010; Baerenfaller et al., 2012; Vile et al., 2012; Bac-Molenaar et al., 2015; Rymaszewski et al., 2017). Here, the focus concerns the preparation and management of experiments, as well as measurements of growth-related traits (e.g., projected rosette area, total leaf area and growth rate), water status-related traits (e.g., leaf dry matter content and relative water content), and plant architecture-related traits (e.g., stomatal density and index and lamina/petiole ratio). Briefly, a completely randomized (block) design is set up in the growth chamber. Next, the substrate is prepared, its initial water content is measured and pots are filled. Seeds are sown onto the soil surface and germinated prior to the experiment. After germination, soil watering and image (visible, infra-red, fluorescence) acquisition are planned by the user and performed by the automaton. Destructive measurements may be performed during the experiment. Data extraction from images and estimation of growth-related trait values involves semi-automated procedures and statistical processing.