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This is the published version of a paper published in Physiologia Plantarum: An International Journal for Plant Biology.
Citation for the original published paper (version of record):
Calderon, R H. (2020)
Red LEDs leave plants singing the blues
Physiologia Plantarum: An International Journal for Plant Biology, 169(1): 7-9 https://doi.org/10.1111/ppl.13106
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I n t h e S p o t l i g h t
Red LEDs leave plants singing the blues
Robert H. Calderon
Department of Plant Physiology, Umeå University, Umeå, Sweden e-mail: robert.calderon@umu.se
Linked article: This spotlight refers to Zheng et al. (2020). To view this article, please visit https://doi.org/10.1111/ppl.13067
Methuselah, a bristlecone pine growing on the slope of a mountain in southeastern California, has almost certainly been growing at the exact location of that same mountain slope where it emerged from a seed over 4700 years ago.
As a consequence of their sessile nature, plants like Methuselah are strictly dependent on their ability to sense and react to their surroundings in order to optimize their chances of survival and reproduction. In nature, rapid and permanent changes to a plant’s light environment are relatively rare. Plants grown for horticulture or agricul- ture, like lettuce or tomatoes, may often be grown under low-light conditions as seedlings before being transferred to high-light environments like greenhouses orfields.
The ability of plants to acclimate from low light to high light has been well-documented, but a thorough under- standing of how the spectral quality of light affects this process is still relatively unknown. Given the prolifera- tion of monochromatic LEDs as low-energy and low-cost options for growing plants in small spaces like green- houses, it is important that the effects of these light sources on plant physiology are understood.
In one of the articles in this issue of Physiologia Plan- tarum, Zheng et al. (2020) have examined the adaptive responses of two ornamental plants under different light regimes: the sun species Chrysanthemum morifolium
‘Bolero’ and the shade species Spathiphyllum wallisii
‘Alfetta’. The plants were grown under low-light condi- tions as young plants and transferred to a high-light greenhouse. Specifically, they grew the young plants under the exact same intensity of either red, blue, red + blue or white light before transferring them to the green- house. Immediately after the transfer, and for the next 30 days, they measured the photosynthetic and photo- protective capacities of the plants.
The authors found that Chrysanthemum and Spathi- phyllum grown under red light were the worst equipped to deal with the initial transfer to the high-light green- house conditions. Both red light-grown species exhibited lower electron transport rates and lower levels of CO2- fixation at the higher light intensities in their first days in the greenhouse. They also had reduced rates of photosys- tem II (PSII) electron transport after the transfer, leading
the authors to hypothesize that these plants might be more prone to photodamage from excess light. To test this, they measured the plants capacity for photoprotection, which involves the dissipation of excess absorbed light energy.
Red-light grown plants had lower levels of regulated photoprotection (ΦNPQ) and higher levels of unregulated energy dissipation (ΦNO), a telltale sign of photodamage.
These negative effects, which the authors speculate might be due to changes in leaf or chloroplast architecture, were still detected up to 8 days after the transfer. At the end of the 30-day experiment, red light-grown Chrysanthemums were found to have lower dry weights than those grown under different light conditions.
Blue light-grown plants also experienced some difficul- ties on theirfirst days in the greenhouse. They showed a reduced capacity for photoprotection under high light and struggled with the initial transfer like their red light- grown counterparts, but they were able to recover with no observed long-term damage. What these observations tell us is that the colors of light that a plant perceives are important for helping it acclimate to future high light inten- sity. This could have implications in understanding the regulation of photoprotection in plants, a process whose manipulation has been shown to have positive effects in crop yield (Kromdijk et al. 2016).
The observations that growth in monochromatic light may have negative consequences for young plants when they are shifted to high-light conditions are especially rel- evant for plant cultivation. Despite the fact that the two plant species in this study appeared to suffer no negative long-term effects when grown under blue and red light together, dichromatic illumination may not be the solu- tion, as it has been reported to result in suboptimal plant growth. Lettuce grown under red and blue light together, for example, were found to have reduced photosynthesis and increased photodamage unless also supplemented with green LEDs (Bian et al. 2018). Horticulturalists and farmers looking to minimize resource usage while maxi- mizing plant productivity, for example, would be wise to consider the potential long-term effects of such mono- chromatic and dichromatic growth regimes for the plants they grow. Further studies are clearly required on the
Physiologia Plantarum 169: 7–9. 2020 ISSN 0031-9317
© 2020 The Author. Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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Physiol. Plant. 169, 2020 8
effects of different combinations of LEDs on the growth of plants and on crop yields. While these studies may not result in plants that produce tomatoes or lettuce over a Methuselah-length lifetime, they will certainly give us a better understanding of how plants adapt to and cope with changes to their light environment.
REFERENCES
Bian Z, Yang Q, Li T, Cheng R, Barnett Y, Lu C (2018) Study of the beneficial effects of green light on lettuce grown
under short-term continuous red and blue light-emitting diodes. Physiol Plant 164: 226–240
Kromdijk J, Głowacka K, Leonelli L, Gabilly ST, Iwai M, Niyogi KK, Long SP (2016) Improving photosynthesis and crop productivity by accelerating recovery from
photoprotection. Science 35: 857–861
Zheng L, Steppe K, Van Labeke MC (2020) Spectral quality of monochromatic LED affects photosynthetic
acclimation to high-intensity sunlight of Chrysanthemum and Spathiphyllum. Physiol Plant 169: 10–26
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