Does Green Really Mean Go? Increasing the Fraction of Green Photons Promotes Growth of Tomato but Not Lettuce or Cucumber.

Boston Swan,Paul Kusuma,Bruce Bugbee

doi:10.3390/plants10040637

Abstract

The photon flux in the green wavelength region is relatively enriched in shade and the photon flux in the blue region is selectively filtered. In sole source lighting environments, increasing the fraction of blue typically decreases stem elongation and leaf expansion, and smaller leaves reduce photon capture and yield. Photons in the green region reverse these blue reductions through the photoreceptor cryptochrome in Arabidopsis thaliana, but studies in other species have not consistently shown the benefits of photons in the green region on leaf expansion and growth. Spectral effects can interact with total photon flux. Here, we report the effect of the fraction of photons in the blue (10 to 30%) and green (0 to 50%) regions at photosynthetic photon flux densities of 200 and 500 µmol m−2 s−1 in lettuce, cucumber and tomato. As expected, increasing the fraction of photons in the blue region consistently decreased leaf area and dry mass. By contrast, large changes in the fraction of photons in the green region had minimal effects on leaf area and dry mass in lettuce and cucumber. Photons in the green region were more potent at a lower fraction of photons in the blue region. Photons in the green region increased stem and petiole length in cucumber and tomato, which is a classic shade avoidance response. These results suggest that high-light crop species might respond to the fraction of photons in the green region with either shade tolerance (leaf expansion) or shade avoidance (stem elongation).

Highlights

Overexpression of cryptochrome in rice led to a significant reduction in the expansion of the secondary leaf blade [70]. These results provide some evidence for the role of cryptochrome in reducing leaf expansion upon blue photon perception
We found no beneficial effect of adding green photons to lettuce or cucumber, but we did see a beneficial effect for both leaf area and dry mass in tomato (Table 2, Figure 3d–f, Figure 4d–f)
Green photons only benefitted tomatoes. These data are contrary to the early findings of Kim et al [5], who found that increased green fraction from fluorescent lamps increased the growth of lettuce compared to light-emitting diode (LED) without green

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Irradiance/photon fluxes in the blue (400 to 500 nm) and red (600 to 700 nm) regions are relatively reduced while the fluxes of photons in the green (500 to 600 nm) and far-red (700 to 750 nm) regions are relatively enriched. The term light is often used to refer to the photon flux, as in blue light, but this terminology does not describe the discrete nature of photons, which drive photobiological reactions. Light is closely connected to brightness in human perception of photons, photon is a preferable term. The terms blue, green, red and far-red photons refer to photons in the regions that induce blue, green, red or far-red color perception

Methods

Discussion

Conclusion