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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.

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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.

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