Green Light Improves Photosystem Stoichiometry in Cucumber Seedlings (Cucumis sativus) Compared to Monochromatic Red Light

Abstract

It has been shown that monochromatic red and blue light influence photosynthesis and morphology in cucumber. It is less clear how green light impacts photosynthetic performance or morphology, either alone or in concert with other wavelengths. In this study, cucumber (Cucumis sativus) was grown under monochromatic blue, green, and red light, dichromatic blue-green, red-blue, and red-green light, as well as light containing red, green, and blue wavelengths, with or without supplemental far-red light. Photosynthetic data collected under treatment spectra at light-limiting conditions showed that both red and green light enhance photosynthesis. However, photosynthetic data collected with a 90% red, 10% blue, 1000 µmol photons m^-2 s^-1, saturating light show significantly lower photosynthesis in the green, red, and red-green treatments, indicating a blue light enhancement due to photosystem stoichiometric differences. The red-green and green light treatments show improved photosynthetic capacity relative to red light, indicating partial remediation by green light. Despite a lower quantum efficiency and the lowest ambient photosynthesis levels, the monochromatic blue treatment produced among the tallest, most massive plants with the greatest leaf area and thickest stems.

Keywords: Cucumis sativus L. (cucumber); blue light; green light; intrinsic water use efficiency (iWUE); light-emitting diode (LED); morphology; photostationary state of phytochrome (PSS); photosynthesis; photosynthetic photon flux density (PPFD); red light; yield photon flux (YPF).

Figure 1

Net photosynthesis (A) vs. cellular CO₂ concentration (C_c) curve fitting for each light treatment. Filled circles represent observed net photosynthesis (A) relative to calculated Cc values. The solid line shows Rubisco limitation, while the dotted line fits RuBP limitation. Triose-phosphate utilization (TPU) limitation was not apparent.

Figure 2

Net photosynthesis (A) under ambient treatment lighting. Different lowercase letters indicate significant differences (p ≤ 0.05; n = 6). Error bars are the standard error. Uppercase letters indicate light treatments.

Figure 3

Profile and overhead images of representative plants, chosen by selecting the plant that was closest in dry weight and height to the treatment average. This image is a composite to allow for visual comparison between treatments. Cucumber seedlings were grown under blue (B), green (G), green–blue (GB), red (R), red–blue (RB), red–green (RG), red–green–blue (RGB), and red–green–blue with far-red (RGB + FR) light. The white bar in the upper middle is 10 cm for profile images, while the yellow bar in the lower middle is 10 cm for overhead images.

Figure 4

Shoot characteristics of cucumber under diverse spectra. Different lowercase letters indicate significant differences (p ≤ 0.05; n is between 25 and 30 for each treatment). Uppercase letters indicate light treatments.

Figure 5

(A): Stomatal conductance under saturating light by light treatment. Different lowercase letters indicate significant differences (p ≤ 0.05; n is between 25 and 30 for each treatment). (B): Stomatal conductance under ambient, treatment lighting (Stomatal conductance_A) vs. adaxial stomatal density. (C): Net photosynthesis under ambient, treatment lighting vs. stomatal conductance under ambient, treatment lighting. (D): Water content vs. instantaneous water use efficiency. (E): Stomatal conductance under saturating light vs. stomatal conductance under ambient, treatment lighting. (F): Water content vs. abaxial stomatal density. Uppercase letters indicate light treatments.

Figure 6

Light treatment spectra: monochromatic blue (B), monochromatic green (G), monochromatic red (R), green–blue (GB), red–blue (RB), red–green (RG), red–green–blue (RGB), and red–green–blue with far red (RGB + FR).