Effects of Long-term Exposure to Different O₂ Concentrations on Growth and Phytochemical Content in Red Leaf Lettuce

Abstract

Oxygen gas is one of the environmental factors closely related to photosynthesis and respiration. In this article, we investigated the effects of long-term exposure to different O2 concentrations on growth and phytochemical contents in leaf lettuce. In order for provide exposure to low O2 for longer periods, we developed a new growth chamber combined with N2 gas generator. Plants were hydroponically cultured under 3, 10 or 21% O2. The leaf area of the plants grown at 3% O2 was significantly smaller than that for plants grown at 21% O2; however, there was no significant difference in dry weight. Owing to this, the specific leaf area of plants grown at 3% O2 was significantly lower than that for plants grown at 21% O2. While the nitrogen content of plants grown at 3% O2 was significantly lower than that for plants grown at 21% O2, the anthocyanin content of plants grown at 3 and 10% O2 was significantly higher than that for plants grown at 21% O2. According to results, we discussed that reduced leaf expansion observed in plants grown at low O2 was the result of the decreased nitrogen.

Responses of growth, photosynthesis, and associated components to hypoxia at different light intensities in red leaf lettuce

“…Some researchers have reported similar results using leaf lettuce (Iwabuchi et al, 1996;Rajapakse et al, 2009;Kawasaki et al, 2015). In a previous study, we showed that the nitrogen and carbon content was affected by hypoxia treatment, and expected an increase in sucrose content (Kawasaki et al, 2015). In the present study, the decrease of nitrogen and increase of carbon and sucrose content in each leaf under hypoxic conditions was reconfirmed (Table 2).…”

“…Moreover, the reduction was induced only during the light period; hence, they speculated that the leaf expansion response was not associated with respiration or photorespiration because C 4 plants concentrate CO 2 in the bundle sheath cells, inhibiting photorespiratory metabolism (Taiz and Zeiger, 2010). We also reported a decrease in leaf area with long-term hypoxia treatment (3% O 2 ) during the light period in red leaf lettuce (Kawasaki et al, 2015). Also, we found a decrease in the specific leaf area of plants grown at 3% O 2 .…”

“…Therefore, we inferred that the accumulation of soluble sugar in leaves occurred under hypoxic conditions, and that this was a factor in the thickening of leaves. In addition, anthocyanin content of plants grown at 3 and 10% O 2 was considerably higher than that of plants grown at 21% O 2 (Kawasaki et al, 2015). Rajapakse et al (2009) and He et al (2013) also showed an increase in anthocyanin content in plants grown under hypoxic conditions.…”

“…A detailed description and a schematic view of the chamber have been presented by Kawasaki et al (2015). Briefly, the chamber dimensions are W 1800 × D 1000 × H 1800 mm.…”

“…investigators have reported the reduced leaf expansion of plants grown under hypoxic conditions for a long period (Fukuyama et al, 1974a(Fukuyama et al, ,b, 1975Takeda et al, 1978;Iwabuchi et al, 1996;Kawasaki et al, 2015). Takeda et al (1978) evaluated the effect of long-term hypoxia treatment on the growth of C 3 and C 4 plants and found reductions in leaf expansion in both types under hypoxic conditions.…”