Magic Blue Light: A Versatile Mediator of Plant Elongation

Abstract

Blue light plays an important role in regulating plant elongation. However, due to the limitations of older lighting technologies, the responses of plants to pure blue light have not been fully studied, and some of our understandings of the functions of blue light in the literature need to be revisited. This review consolidates and analyzes the diverse findings from previous studies on blue-light-mediated plant elongation. By synthesizing the contrasting results, we uncover the underlying mechanisms and explanations proposed in recent research. Moreover, we delve into the exploration of blue light-emitting diodes (LEDs) as a tool for manipulating plant elongation in controlled-environment plant production, highlighting the latest advancements in this area. Finally, we acknowledge the challenges faced and outline future directions for research in this promising field. This review provides valuable insights into the pivotal role of blue light in plant growth and offers a foundation for further investigations to optimize plant elongation using blue light technology.

Keywords: applications; blue LED; future directions; mechanisms; plant elongation.

Figure 1

Plant elongation responses to pure and impure blue light in four ornamental plant species [43]. R = narrow-band red LED as a control treatment; B = pure blue light from a narrow-band blue LED; BR = impure blue light created by mixing B with a small amount (10% total PPFD) of R; BRF = impure blue light created by mixing BR with a small amount of far-red light, with red/far-red ≈ 1. The PPFD of the LED lighting was either 50 or 100 µmol m⁻² s⁻¹ for all treatments. The reference bar length in these pictures is 8.5 cm.

Figure 2

Plant elongation responses to blue or red LED light for different plant genotypes. R = red LED; B = blue LED. The PPFD of the LED lighting was 100 µmol m⁻² s⁻¹ for both treatments. The reference bar length in these pictures is 2.8 cm for (A,B) and 1.6 cm for (C–E). This figure is part of our unpublished works.

Figure 3

Plants’ elongation responses to blue or red LED light when growing at commercial planting intensity or in rockwool cubes. R = red LED; B = blue LED. The PPFD of the LED lighting was 100 µmol m⁻² s⁻¹ for both treatments. The reference bar length in these pictures is 4.3 cm for (A) and 2.5 cm for (B–D). This figure is part of our unpublished works.

Figure 4

Leaf epinasty under red LEDs and leaf hyponasty under blue LEDs for sunflower microgreens. R = red LED; B = blue LED. The PPFD of LED lighting was 50 µmol m⁻² s⁻¹ (A,B) or 100 µmol m⁻² s⁻¹ (C,D) for both treatments. The reference bar length in these pictures is 2 cm. This figure is part of our unpublished works.

Figure 5

Epidermis cells of sunflower cotyledons under red or blue LED light. R = red LED; B = blue LED. The PPFD of LED lighting was 100 µmol m⁻² s⁻¹ for both treatments. The reference bar length in these pictures is 100 µm for (A–D) and 500 µm for (E,F). This figure is part of our unpublished works.

Figure 6

A proposed simple model for explaining the mechanisms involved in blue-LED-promoted plant elongation. BL = blue light; PPS = phytochrome photostationary state; phy = phytochrome; cry = cryptochrome; phot = phototropin; GA = gibberellic acid; BR = brassinosteroid. Light stimulus; promotional signal; speculated promotional signal; inhibitory signal; speculated inhibitory signal; speculated involved hormone; speculated affecting factor. The proposed model is based on the key findings from our previous studies [30,31,32,33,34,35,36,40,41,42,43,46,47,48], except for the GA signal from Fukuda’s group [17].

Figure 7

Potential ways to apply blue LEDs in plant production in a controlled environment. FR = far-red.