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Physiological Responses of Cucumber Seedlings to Different Supplemental Light Duration of Red and Blue LED.

ABSTRACT: Normal development of plants is inhibited by inadequate light in winter in greenhouses in Northwest China. Growth lamps, using light-emitting diodes (LEDs) with red blue light (7R2B), were used to supplement daylight for 1, 2, and 3 h. Seedling growth, photosynthesis, and photosynthetic product; the Calvin cycle key and sugar metabolism-related enzymes and their encoding genes; and the light signal sensing regulation of key gene expression were studied in greenhouse cucumbers under three treatments to determine the best supplemental light durations to enhance cucumber cultivation in greenhouses in winter. Treatment with LED red and blue light for 3 h significantly promoted the growth and development of cucumbers, root growth, and dry matter accumulation. It improved the photosynthetic rate, photosynthetic pigment content, and light energy utilization efficiency in cucumbers. Supplementation with red and blue LED light for 3 h upregulated the expression levels of key genes encoding the Calvin cycle and enzymes related to sugar metabolism in cucumber leaves, which promoted the synthesis and accumulation of photosynthates. The expression levels of phytochrome B, cryptochrome 1, and hypocotyl 5 in the cucumber leaves were also significantly upregulated after 3 h of light supplementation. Combined LED red and blue light for 3 h should be used to supplement natural light to enhance the cucumber cultivation in greenhouses in winter.

SUBMITTER: Wang S

PROVIDER: S-EPMC8311605 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Light is one of the most important environmental signals in plant growth, development, and stress response. Green light has been proved to enhance plant defense against biotic and/or abiotic stress. To illustrate the effects of green light partially replaced red light and blue light on the plant under drought condition, cucumber (Cucumis sativus L. cv. Xinchun No. 4) seedlings were treated with short-term drought stress and were concomitantly exposed to four treatments, which were set up by adjusting the relative amount of green light as 0 (RB), 25 (RBG25), 50 (RBG50), and 75 (RBG75) μmol m-2 s-1, respectively, with a total photosynthetic photon flux density of 250 μmol m-2 s-1 and a fixed red-to-blue ratio of 4:1. The results showed that compared with RB, RBG50 significantly increased shoot fresh weight (FW) and dry weight (DW), root DW, plant height, stem diameter, leaf area, and leaf dry mass per unit area (LMA) by 10.61, 7.69, 66.13, 6.22, 10.02, 4.10, and 12.41%, respectively. Also, the addition of green light significantly increased the root volume and root tip number. Moreover, green light partial replacement of red light and blue light increased total water content, especially free water content, improved leaf water status, and alleviated water loss in plants caused by drought stress. Also, the addition of green light increased net photosynthetic rate (Pn), reduced both stomata conductance (gs) and transpiration rate (E), enhanced the intrinsic water-use efficiency (WUE) and instantaneous water-use efficiency (iWUE) of leaves, and increased the content of chlorophylls a and b. Green light substituting a proportion of blue and red light regulated stomatal aperture by significantly increasing abscisic acid (ABA) and γ-aminobutyric acid (GABA) content. In addition, the increase of GABA was resulted from the upregulation of Glutamate Decarboxylase 2 (CsGAD2). However, the relative electrolytic leakage and contents of malondialdehyde (MDA), superoxide anion ( O2- ), and hydrogen peroxide (H2O2) vigorously decreased as the intensity of green light was added to the spectrum under drought. Conclusively, green light partially replaced red light and blue light and improved drought tolerance of cucumber seedlings by upregulating the expression of CsGAD2 gene and promoting the synthesis of GABA. The increase in GABA content further downregulated the expression of aluminum-activated malate transporter 9 (CsALMT9) gene, induced stomata to close, improved water utilization, and alleviated damage caused by drought. This study highlights a role of green light in plant physiological processes. Moreover, analyzing the function of green light on improving drought tolerance of plants could open alternative avenues for improving plant stress resilience.

Project description:Raising young plants is important for modern greenhouse production. Upon transfer from the raising to the production environment, young plants should maximize light use efficiency while minimizing deleterious effects associated with exposure to high light (HL) intensity. The light spectrum may be used to establish desired traits, but how plants acclimated to a given spectrum respond to HL intensity exposure is less well explored. Cucumber (Cucumis sativus) seedlings were grown in a greenhouse in low-intensity sunlight (control; ∼2.7 mol photons m-2 day-1) and were treated with white, red, blue, or green supplemental light (4.3 mol photons m-2 day-1) for 10 days. Photosynthetic capacity was highest in leaves treated with blue light, followed by white, red, and green, and was positively correlated with leaf thickness, nitrogen, and chlorophyll concentration. Acclimation to different spectra did not affect the rate of photosynthetic induction, but leaves grown under blue light showed faster induction and relaxation of non-photochemical quenching (NPQ) under alternating HL and LL intensity. Blue-light-acclimated leaves showed reduced photoinhibition after HL intensity exposure, as indicated by a high maximum quantum yield of photosystem II photochemistry (F v /F m ). Although plants grown under different supplemental light spectra for 10 days had similar shoot biomass, blue-light-grown plants (B-grown plants) showed a more compact morphology with smaller leaf areas and shorter stems. However, after subsequent, week-long exposure to full sunlight (10.7 mol photons m-2 day-1), B-grown plants showed similar leaf area and 15% higher shoot biomass, compared to plants that had been acclimated to other spectra. The faster growth rate in blue-light-acclimated plants compared to other plants was mainly due to a higher photosynthetic capacity and highly regulated NPQ performance under intermittent high solar light. Acclimation to blue supplemental light can improve light use efficiency and diminish photoinhibition under high solar light exposure, which can benefit plant growth.

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Physiological Responses of Cucumber Seedlings to Different Supplemental Light Duration of Red and Blue LED.

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