GLO-Roots: Growth and Luminescence Observatory is a collaborative effort between the labs of José R. Dinneny at Carnegie Institution for Science, Rubén Réllan-Álvarez at Langebio, Mexico and Guillame Lobet at the University of Liége, Belgium.
Raw Image data from Réllan-Álvarez et al. at Dryad
More information to follow!
We have recently developed a new imaging platform (GLO-Roots: Growth and Luminescence Observatory for Roots, U.S. patent application 13/970,960), which allows root architecture and gene expression to be studied in soil-grown plants (Rellán-Álvarez et al. 2015). GLO-Roots is composed of custom growth vessels, luminescent reporters and imaging systems. We use rhizotrons (thin transparent pots, dimensions: 15cm x 30cm x 2 mm) that have equivalent soil volumes to small pots (100 cm3) and support growth from germination to senescence. Shoot weight is not significantly different from pot-grown plants, but is greater than plants grown in gel-based systems. Roots show no evidence of constriction compared to pot or cylindrical growth vessels with the same soil volume (Rellán-Álvarez et al. 2015).
To visualize roots, we designed plant-codon optimized luciferase reporters that emit light of different wavelengths (LUC2o: 580 nm, PPyRE8o: 620 nm, Fig 1C). Constitutive expression of PPyRE8 is used to track root growth while the transcriptional response of a gene of interest can be studied by fusing LUC2o to any characterized promoter. To visualize reporter expression, plants are watered with a luciferin solution and imaged afterwards. We have designed a custom luminescence imaging system that automatically captures pictures of rhizotrons held vertically. The signal from each reporter is distinguished using band-pass filters held in a motorized wheel, which enables automated acquisition of images from plants expressing both structural and environmentally-responsive reporters. In collaboration with Guillame Lobet (Univ. of Liége, Belgium) we have developed GLO-RIA (GLO-Roots Image Analysis) software that allows for automated determination of root system area, convex hull, depth, width and directionality, which quantifies the angle that root segments make with respect to gravity. GLO-RIA is also able to relate root system parameters to local root-associated variables such as reporter expression intensity or soil-moisture content.
GLO-Roots provides important advantages over gel-based systems for studying WD responses: 1) Shoots are exposed to the atmosphere and vapor pressure deficit (VPD) is maintained at levels that allow for transpiration of water from the shoot. 2) Roots are protected from light, which is a well-characterized stimulus that affects root GSA. 3) Gene expression analysis shows that pot-grown roots have greater similarity in gene expression patterns to rhizotron-grown roots than to roots grown on gel-based plates (Rellan-Alvarez et al. 2015). 4) WD can be simulated in more realistic ways than in gel. Soil in rhizotrons is exposed to air at the top and dries from the top-down. Drying soil increases volume occupied by air-spaces, reducing contact of the root with liquid water. These effects are similar to changes in soil expected in the field during WD. 5) Changes in the optical properties of drying soil enable estimates of moisture content to be made based on analysis of bright-field images.