LED light gradient as a screening tool for light quality responses in model plant species

  1. P. Lejeune
  2. A. Fratamico
  3. F. Bouché
  4. S. Huerga Fernández
  5. P. Tocquin
  6. C. Périlleux

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Abstract

Current developments in light-emitting diodes (LEDs) technologies have opened new perspectives for sustainable and highly efficient indoor cultivation. The introduction of LEDs not only allows a reduction in the production costs on a quantitative level, it also offers opportunities to manipulate and optimise qualitative traits. Indeed, while plants respond strongest to red and blue lights for photosynthesis, the whole light spectrum has an effect on plant shape, development, and chemical composition. In order to evaluate LEDs as an alternative to traditional lighting sources, the species-specific plant responses to distinct wavelengths need to be evaluated under controlled conditions. Here, we tested the possibility to use light composition gradients in combination with semi-automated phenotyping to rapidly explore the phenotypic responses of different species to variations in the light spectrum provided by LED sources. Plants of seven different species ( Arabidopsis thaliana, Ocimum basilicum, Solanum lycopersicum, Brachypodium distachyon, Oryza sativa, Euphorbia peplus, Setaria viridis ) were grown under standard white fluorescent light for 30 days, then transferred to a Red:Blue gradient for another 30 days and finally returned to white light. In all species, differences in terms of dimension, shape, and color were rapidly observed across the gradient and the overall response was widely species-dependent. The experiment yielded large amounts of imaging-based phenotypic data and we suggest simple data analysis methods to aggregate the results and facilitate comparisons between species. Similar experimental setups will help achieve rapid environmental optimization, screen new crop species and genotypes, or develop new gene discovery strategies.

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  1. GigaScience

    This work has been peer reviewed in GigaScience (see paper https://doi.org/10.1093/gigascience/giab101), which carries out open, named peer-review.

    These reviews are published under a CC-BY 4.0 license and were as follows:

    Reviewer 2: Filippos Bantis

    The authors used imaging tools with three types of phenotypic descriptors (dimensions, shape, colour indices) and side- or top-camera views in order to determine non-destructive parameters of seven diverse species (Arabidopsis thaliana, Brachypodium distachyon, Euphorbia peplus, Ocimum basilicum, Oryza sativa, Solanum lycopersicum, and Setaria viridis) growing under different Red/Blue gradients (from 100% Blue to 100% Red). The results are important since they are non-destructive and provide a good basis for the selection of light treatments for specific plants in controlled environment agriculture. The introduction is informative and sufficiently describes the scope of the research. I like the way the authors describe/display the results. Relatively few words (compared to the volume of the obtained measurements) but beautifully built figures which provide all the necessary information. However, I would expect more discussion at the end of each set of parameters results' description, as well as possible comparisons with the literature, even if it is rather scarce. For example, in PDF page 11, subsection "Patterns of change over time", the results are barely discussed. Moreover, the review process would be facilitated if the manuscript had line numbering.

    Specific comments are following:

    • In the title, LED should be written with capital letters, not Led

    • Keywords must not be included in the title. Please remove or substitute LED and light quality Introduction * PDF page 4, L3. Controlled environment agriculture must be abbreviated the first time it is written in the text. The same applies with other terms such as RGB.

    • PDF page 5, L23. "Large-scale crops" is more appropriate term.

    • I agree with the active voice in the objectives' part of the introduction. However, you should refrain from beginning most sentences with "we". Results

    • PDF page 8. I suggest that "Data description" subsection is moved in the "Methods" section

    • This section should be renamed to "Results and Discussion" since there is also discussion within the results. Methods

    • PDF page 14. How many cabinets were used? How many treatments and plants were placed in each cabinet? Apart from figure 1 depiction, you should also describe the experimental design in order for the reader (and me as well) to fully understand it.

  2. GigaScience

    This work has been peer reviewed in GigaScience (see paper https://doi.org/10.1093/gigascience/giab101), which carries out open, named peer-review.

    These reviews are published under a CC-BY 4.0 license and were as follows:

    Reviewer 1: Yujin Park

    The manuscript presents the result of an experiment investigating the impact of red:blue ratio of light gradient on plant phenotypic traits in seven plant species. The subject of the manuscript is very innovative and interesting, but there are parts of the materials and methods that are less clear. Specific comments:

    • In this study, plant phenotypic traits were evaluated using an imaging platform. Plant biomass (fresh and dry weights of shoot and root) is one of the most important plant growth parameters. Are there any suggestions that plant biomass can be predicted from the plant phenotypic traits quantified by the imaging platform?

    • Growth conditions:

    • Does the irradiance of 130-150 µE∙m-2∙s-1 indicate the PPFD (400-700 nm)? How was it measured?

    • Please be consistent for the unit for photon flux density throughout the manuscript. µEinsteins were interchangeably used along with µmol∙m-2∙s-1 in the past, but the Einstein is not a unit in the SI of units. Thus, please use µmol∙m-2∙s-1 when you quantify the photon flux density. Also, please revise the µmoles∙m-2∙s-1 in Fig. 1 into µmol∙m-2∙s-1.

    • Could you provide the spectral distribution data for white light, red LED, and blue LED used in this study?

    • For the concentration of the slow release fertilizer, do you mean gram per liter? If so, please correct it to 6 g∙L-1.

    • What was the growing conditions (air temperature, relative humidity, photoperiod, etc) during the treatment of red:blue gradient?

    • Did you keep the control plants under white light continuously? Then, did you make sure that the control plants and treatment plants are grown under the same growing condition except for the light quality treatment?

    • It is not clear whether the experiment was replicated. The experimental unit is the physical entity which can be assigned, at random, to a treatment. Here the experiment unit was the experimental plot under each light gradient treatment. A single plant should be treated as an observational unit. So, without replications, the data is less reliable.

  3. Version published to 10.1101/2020.10.08.320002v1 on bioRxiv