T Shibuya, R Endo, N Hayashi, Y Kitaya – Photosynthetica
This study evaluated the photosynthetic responses of Cucumis sativus leaves acclimated to illumination from three-band white fluorescent lamps with a high red:far-red (R:FR) ratio (R:FR = 10.5) and the photosynthetic responses of leaves acclimated to metal-halide lamps that provided a spectrum similar to that of natural light (R:FR = 1.2) at acclimation photosynthetic photon flux density (PPFD) of 100 to 700 μmol m–2 s–1. The maximum gross photosynthetic rate (PG) of the fluorescent-acclimated leaves was approximately 1.4 times that of the metal-halide-acclimated leaves at all acclimation PPFDs. The ratio of quantum efficiency of photosystem II (ФPSII) of the fluorescent-acclimated leaves to that of the metal-halide-acclimated leaves tended to increase with increasing acclimation PPFD, whereas the corresponding ratios for the leaf mass per unit area tended to decrease with increasing acclimation PPFD. These results suggest that the greater maximum PG of the fluorescent acclimated leaves resulted from an interaction between the acclimation light quality and quantity, which was mainly caused by the greater leaf biomass for photosynthesis per area at low acclimation PPFDs and by the higher ФPSII as a result of changes in characteristics and distribution of chloroplasts, or a combination of these factors at high acclimation PPFDs… The light: dark period was 12:12 h throughout the acclimation period. The spectrum under each light source (Fig. 1) was measured using a BLK-CXR-SR spectrometer (StellarNet Inc., Tampa, FL, USA) at the level of the leaf surface.
![Fig. 1. Spectra of light produced by the (A) fluorescent lamps with a high red:far-red (R:FR) ratio and (B) metal-halide lamps that provided a spectrum similar to that of natural light measured at the leaf surface. Relative photon flux densities were expressed in values relative to the maximum. R:FR ratio was estimated by dividing the cumulative photon flux density [μmol m–2 s–1] from red light (600 to 700 nm) by that from far-red light (700 to 800 nm) light. The plants were shielded from the metal-halide light by a water filter to avoid leaf temperature increases.](https://www.stellarnet.us/wp-content/uploads/illumination-of-Cucumis-Sativius-leaves.jpg)
Fig. 1. Spectra of light produced by the (A) fluorescent lamps with a high red:far-red (R:FR) ratio and (B) metal-halide lamps that provided a spectrum similar to that of natural light measured at the leaf surface. Relative photon flux densities were expressed in values relative to the maximum. R:FR ratio was estimated by dividing the cumulative photon flux density [μmol m–2 s–1] from red light (600 to 700 nm) by that from far-red light (700 to 800 nm) light. The plants were shielded from the metal-halide light by a water filter to avoid leaf temperature increases.
