In rice plants grown under red light supplemented with blue light (red/blue-light PPFD ratio was 4/1), photosynthetic rates per unit leaf area measured under white light at 1,600 and 250 micromol m-2) s-1 were higher than those in the plants grown under red light alone. The higher photosynthetic rates were associated with higher total N content of leaves, which was accompanied by larger amounts of key components of photosynthesis-limiting processes, including Rubisco, Cyt f, Chl and LHCII. These results suggested that the increase in total N content of leaves induced by supplemental blue light enhanced both light-saturated and light-limited photosynthesis.
Blue light has been suggested to participate in the acclimation of photosynthesis to growth irradiance. We analyzed the effects of blue light intensity on the photosynthetic properties of leaves with regard to acclimation to irradiance. Spinach (Spinacia oleracea L.) plants were grown under mixtures of blue and red light with blue‐light photon flux densities (PFDs) of 0, 30, 100 and 150 µmol m−2 s−1 at a total photosynthetic PFD of 300 µmol m−2 s−1. The light‐saturated rate of photosynthesis under white light, leaf N content per unit leaf area, leaf dry weight per unit leaf area and the ratio of cytochrome (Cyt) f content to light‐harvesting chlorophyll‐binding protein of photosystem II (LHCII) content were evaluated. The photosynthetic rate tended to increase with increasing blue‐light PFD up to 100 µmol m−2 s−1, and this was associated with an increase in leaf N content per unit leaf area. However, the increase in leaf N content per unit leaf area did not necessarily result from an increase in leaf dry weight per unit leaf area. The Cyt f to LHCII content ratio increased linearly with increasing blue‐light PFD up to 100 µmol m−2 s−1, indicating that plants grown under higher blue‐light PFD up to this value resembled plants grown under higher irradiance in terms of N partitioning between electron‐transport components and light‐harvesting components. This result suggests that the level of blue light is involved only in the acclimation to relatively low growth irradiances at the chloroplast level.
The effects of blue light supplementation to red light on growth, morphology and N utilization in rice plants (Oryza sativa L. cv. Sasanishiki and Nipponbare) were investigated. Plants were grown under two light quality treatments, red light alone (R) or red light supplemented with blue light (RB; red/blue-light photosynthetic photon flux density [PPFD] ratio was 4/1), at 380 µmol m −2 s −1 PPFD. The biomass production of both cultivars grown under RB conditions was higher than that of plants grown under R conditions. This enhancement of biomass production was caused by an increase in the net assimilation rate (NAR). The higher NAR was associated with a higher leaf N content per leaf area at the whole-plant level, which was accompanied by higher contents of the key components of photosynthesis, including Rubisco and chlorophyll. In Sasanishiki, preferential biomass investment in leaf blades and expansion of wider and thinner leaves also contributed to the enhancement of biomass production. These morphological changes in the leaves were not observed in Nipponbare. Both the changes in physiological characteristics, including leaf photosynthesis, and the changes in morphological characteristics, including leaf development, contributed to the enhancement of biomass production under RB conditions, although the extent of these changes differed between the two cultivars.
Blue light effects on the acclimation of energy partitioning characteristics in PSII and CO2 assimilation capacity in spinach to high growth irradiance were investigated. Plants were grown hydroponically in different light treatments that were a combination of two light qualities and two irradiances,i.e. white light and blue-deficient light at photosynthetic photon flux densities (PPFDs) of 100 and 500 micromol m(-2) s(-1). The CO2 assimilation rate, the quantum efficiency of PSII(PhiPSII) and thermal dissipation activity (F(v)/F(m)-F'(v)/F'(m)) in young, fully expanded leaves were measured under 1,600 micromol m(-2) s(-1) white light. The CO2 assimilation rate and (PhiPSII) were higher, while F(v)/F(m)-F'(v)/F'(m) was lower in plants grown under high irradiance than in plants grown under low irradiance. These responses were observed irrespective of the presence or absence of blue light during growth. The extent of the increase in the CO2 assimilation rate and PhiPSII and the decrease in F(v)/F(m)-F'(v)/F'(m) by high growth irradiance was smaller under blue light-deficient conditions. These results indicate that blue light helps to boost the acclimation responses of energy partitioning in PSII and CO2 assimilation to high irradiance. Similarly, leaf N, Cyt f and Chl contents per unit leaf area increased by high growth irradiance, and the extent of the increment in leaf N, Cyt f and Chl was smaller under blue light-deficient conditions. Regression analysis showed that the differences in energy partitioning in PSIIand CO2 assimilation between plants grown under high white light and high blue-deficient light were closely related to the difference in leaf N.
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