Accelerated high-throughput imaging and phenotyping system for small organisms

Caloric restriction extends lifespan in a clonal plant

When subjected to dietary caloric restriction (CR), individual animals often outlive well-fed conspecifics. Here, we address whether CR also extends lifespan in plants. Whereas caloric intake in animals comes from ingestion, in plants it derives from photosynthesis. Thus, factors that reduce photosynthesis, such as reduced light intensity, can induce CR. In two lab experiments investigating the aquatic macrophyte Lemna minor, we tracked hundreds of individuals longitudinally, with light intensity-and hence, CR-manipulated using neutral-density filters. In both experiments, CR dramatically increased lifespan through a process of temporal scaling. Moreover, the magnitude of lifespan extension accorded with the assumptions that (a) light intensity positively relates to photosynthesis following Michaelis-Menten kinetics, and (b) photosynthesis negatively relates to lifespan via a power law. Our results emphasize that CR-mediated lifespan extension applies to autotrophs as well as heterotrophs, and suggest that variation in light intensity has quantitatively predictable effects on plant aging trajectories.

The Duckbot: A system for automated imaging and manipulation of duckweed

Laboratory automation can boost precision and reproducibility of science workflows. However, current laboratory automation systems are difficult to modify for custom applications. Automating new experiment workflows therefore requires development of one-off research platforms, a process which requires significant time, resources, and experience. In this work, we investigate systems to lower the threshold to automation for plant biologists. Our approach establishes a direct connection with a generic motion platform to support experiment development and execution from a computational notebook environment. Specifically, we investigate the use of the open-source tool-changing motion platform Jubilee controlled using Jupyter notebooks. We present the Duckbot, a machine customized for automating laboratory research workflows with duckweed, a common multicellular plant. The Duckbot comprises (1) a set of end-effectors relevant for plant biology, (2) software modules which provide flexible control of these tools, and (3) computational notebooks which make use of these tools to automate duckweed experiments. We demonstrate the Duckbot's functionality by automating a particular laboratory research workflow, namely, duckweed growth assays. The Duckbot supports setting up sample plates with duckweed and growth media, gathering image data, and conducting relevant data analysis. We discuss the opportunities and limitations for developing custom laboratory automation with this platform and provide instructions on usage and customization.

Comparative Phytotoxicity of Metallic Elements on Duckweed Lemna gibba L. Using Growth- and Chlorophyll Fluorescence Induction-Based Endpoints

In this study, we exposed a commonly used duckweed species-Lemna gibba L.-to twelve environmentally relevant metals and metalloids under laboratory conditions. The phytotoxic effects were evaluated in a multi-well-plate-based experimental setup by means of the chlorophyll fluorescence imaging method. This technique allowed the simultaneous measuring of the growth and photosynthetic parameters in the same samples. The inhibition of relative growth rates (based on frond number and area) and photochemical efficiency (Fv/Fo and Y(II)) were both calculated from the obtained chlorophyll fluorescence images. In the applied test system, growth-inhibition-based phytotoxicity endpoints proved to be more sensitive than chlorophyll-fluorescence-based ones. Frond area growth inhibition was the most responsive parameter with a median EC50 of 1.75 mg L-1, while Fv/Fo, the more responsive chlorophyll-fluorescence-based endpoint, resulted in a 5.34 mg L-1 median EC50 for the tested metals. Ag (EC50 0.005-1.27 mg L-1), Hg (EC50 0.24-4.87 mg L-1) and Cu (EC50 0.37-1.86 mg L-1) were the most toxic elements among the tested ones, while As(V) (EC50 47.15-132.18 mg L-1), Cr(III) (EC50 6.22-19.92 mg L-1), Se(VI) (EC50 1.73-10.39 mg L-1) and Zn (EC50 3.88-350.56 mg L-1) were the least toxic ones. The results highlighted that multi-well-plate-based duckweed phytotoxicity assays may reduce space, time and sample volume requirements compared to the standard duckweed growth inhibition tests. These benefits, however, come with lowered test sensitivity. Our multi-well-plate-based test setup resulted in considerably higher median EC50 (3.21 mg L-1) for frond-number-based growth inhibition than the 0.683 mg L-1 median EC50 derived from corresponding data from the literature with standardized Lemna-tests. Under strong acute phytotoxicity, frond parts with impaired photochemical functionality may become undetectable by chlorophyll fluorometers. Consequently, the plant parts that are still detectable display a virtually higher average photosynthetic performance, leading to an underestimation of phytotoxicity. Nevertheless, multi-well-plate-based duckweed phytotoxicity assays, combined with chlorophyll fluorescence imaging, offer definite advantages in the rapid screening of large sample series or multiple species/clones. As chlorophyll fluorescence images provide information both on the photochemical performance of the test plants and their morphology, a joint analysis of the two endpoint groups is recommended in multi-well-plate-based duckweed phytotoxicity assays to maximize the information gained from the tests.