Author
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Nelson, Sven |
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Oliver, Melvin |
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Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/5/2017 Publication Date: 7/19/2017 Publication URL: https://handle.nal.usda.gov/10113/5832866 Citation: Nelson, S.K., Oliver, M.J. 2017. A soil-plate based pipeline for assessing cereal root growth in response to polyethylene glycol (PEG)-induced water deficit stress. Frontiers in Plant Science. 8:1272. https://doi.org/10.3389/fpls.2017.01272. DOI: https://doi.org/10.3389/fpls.2017.01272 Interpretive Summary: In order to develop strategies for improving drought tolerance, it is necessary to understand how plant roots respond to drying soils, but the methods currently available for studying root traits under controlled conditions often rely on growth under unrealistic laboratory conditions. The article describes a novel method for measuring seedling root growth in soils that have reduced water availability, simulating drought. This method provides the ability to study seedlings in soil, rather than in artificial medias that do not accurately mimic soil. It also provides the ability to measure many roots quickly and accurately using digital photography. Root lengths are determined by image analysis and data analysis is performed using a small and simple to use computer program written for this study. This computerized data “pipeline” reduces the time and effort required to analyze the effect of low soil moisture on root growth. The research has established a simple, easy to use method for breeders to screen cultivars of any cereal crop for root traits that impact the drought tolerance of the crop. This method will speed up our efforts to develop drought tolerant crops. Technical Abstract: Drought is a serious problem that causes losses in crop-yield every year, but the mechanisms underlying how roots respond to water deficit are difficult to study under controlled conditions. Methods for assaying root elongation and architecture, especially for seedlings, are commonly achieved on artificial media, such as agar, moistened filter paper, or in hydroponic systems. However, it has been demonstrated that measuring root characteristics under such conditions does not accurately mimic what is observed when plants are grown in soil. Morphological changes in root behavior occur because of differences in solute diffusion, mechanical impedance, exposure to light (in some designs), and gas exchange of roots grown under these conditions. To address such deficiencies, we developed a quantitative method for assaying seedling root lengths and germination in soil using a plate-based approach with wheat as a model crop. We also further developed the method to include defined water deficits stress levels using the osmotic properties of polyethylene glycol (PEG). Seeds were sewn into soil-filled vertical plates and grown in the dark. Root length measurements were collected using digital photography through the transparent lid under plant-safe green lighting. Photographs were analyzed using the cross-platform ImageJ plugin, SmartRoot, which can detect root edges and partially automate root calling. This allowed for quick measurements and straightforward and accurate assessments of non-linear roots. Other measurements, such as root width or angle, can also be collected by this method. An R function was developed to collect exported root length data, process and reformat the data, and output plots depicting root/shoot growth dynamics. For water deficit experiments, seedlings were transplanted side-by-side into well-watered plates and plates containing PEG solutions to simulate precise water deficits. |
