Atmospheric nitric oxide stimulates plant growth and improves the quality of spinach (Spinacia oleracea)

Nitric oxide (NO) is an endogenous signalling molecule implicated in a growing number of plant processes and has been recognised as a plant hormone. The present research employed spinach plant ( Spinacia oleracea cv. Huangjia) and closed growth chambers to investigate the effects of gaseous NO application on vegetable production in greenhouses. Treatment of low concentration of NO gas (ambient atmosphere with 200 nL L^?1 NO gas) significantly increased the shoot biomass of the soil-cultivated plants as compared with the control treatment (ambient atmosphere). In addition, the NO treatment also increased the photosynthetic rate of leaves, indicating that the enhancement of photosynthesis is an important reason leading to more biomass accumulation induced by NO gas. Furthermore, the NO treatment decreased nitrate concentration but increased the concentrations of soluble sugar, protein, antioxidants (vitamin C, glutathione and flavonoids), and ferric reducing-antioxidant power (FRAP) in shoots of the plants grown in soil, suggesting that the gaseous NO treatment can not only increase vegetable production but also improve vegetable quality. In addition, the effects of the combined application of NO and CO₂ (NO 200 nL L^?1 and CO₂ 800 μL L^?1) on shoot biomass was even greater than the effects of elevated CO₂ (CO₂ 800 μL L^?1) or the NO treatment alone, implying that gaseous NO treatment can be used in CO₂-elevated greenhouses as an effective strategy in improving vegetable production.