Abstract
The artificial light used in growth chambers is usually devoid of green (G) light, which is considered to be less photosynthetically efficient than blue (B) or red (R) light. To verify the role of G light supplementation in the spectrum, we modified the RB spectrum by progressively replacing R light with an equal amount of G light. The tomato plants were cultivated under 100 µmol m–2 s–1 of five different combinations of R (35–75%) and G light (0–40%) in the presence of a fixed proportion of B light (25%) provided by light-emitting diodes (LEDs). Substituting G light for R altered the plant’s morphology and partitioning of biomass. We observed a decrease in the dry biomass of leaves, which was associated with increased biomass accumulation and the length of the roots. Moreover, plants previously grown under the RGB spectrum more efficiently utilized the B light that was applied to assess the effective quantum yield of photosystem II, as well as the G light when estimated with CO2 fixation using RB + G light-response curves. At the same time, the inclusion of G light in the growth spectrum reduced stomatal conductance (gs), transpiration (E) and altered stomatal traits, thus improving water-use efficiency. Besides this, the increasing contribution of G light in place of R light in the growth spectrum resulted in the progressive accumulation of phytochrome interacting factor 5, along with a lowered level of chalcone synthase and anthocyanins. However, the plants grown at 40% G light exhibited a decreased net photosynthetic rate (Pn), and consequently, a reduced dry biomass accumulation, accompanied by morphological and molecular traits related to shade-avoidance syndrome.
Highlights
The light environment strongly influences plant development and physiology because the broad-spectrum of incident radiation absorbed by different groups of photoreceptors represents a signal for light-induced photomorphogenesis (Paik and Huq 2019)
Supplementation of the RGB spectrum with up to 30% of G light exerted mostly beneficial effects, whilst the addition of 40% of G light was undesirable as it potentiated the shade-avoidance syndrome (SAS) response and significantly reduced the dry biomass of plants
Replacing G light with R stimulated the elongation of petioles and altered the pattern of biomass accumulation; under RGB light, plants transport more assimilates to the roots rather than to leaves, as compared to those grown under the RB-light-emitting diodes (LEDs)
Summary
The light environment strongly influences plant development and physiology because the broad-spectrum of incident radiation absorbed by different groups of photoreceptors represents a signal for light-induced photomorphogenesis (Paik and Huq 2019). Phytochromes (PHYs) that regulate seed germination, de-etiolation, shade-avoidance syndrome (SAS) responses, circadian clock and blooming are the most sensitive to red (R) and far-red (FR) radiation. UV-A, blue (B) and green (G) light receptive cryptochromes (CRYs) are essential to the regulation of de-etiolation, entrainment of the circadian clock and flowering. Photosynthesis, is driven by the absorption of light via chlorophylls and auxiliary pigments, such as carotenoids. The wavelengths of light that drive photosynthesis are referred to as photosynthetically active radiation (PAR) and range from 400 to 700 nm. Due to different absorption rates, not all wavelengths are efficient in carbon dioxide assimilation (Cope et al 2014)
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