Nitrate Content and Expression of Putative Nitrate Transporter Genes in Lettuce Fertilized with Nitrogen Fertilizers

Nutrient Deficiency Affects the Growth and Nitrate Concentration of Hydroponic Radish

In hydroponics, a continuous supply of mineral nutrients is essential for plant growth. However, constitutive nutrient-rich conditions also increase the nitrate content in the plants, which can be harmful to human health. Here, we investigated the effect of nutrient deficiency on the growth and component composition of hydroponic radish by changing the timing of nutrient removal from the hydroponic solution. Radish plants that were 14 days old were transferred to four different nutrient conditions for 14 days: nutrient deficiency for 14 days (WW), full nutrient for 14 days (NN), nutrient deficiency for the last 7 days (NW), and nutrient deficiency for the first 7 days (WN). After the treatments, the NW plants had similar taproot growth to NN plants. In contrast, the WN plants significantly reduced taproot growth. The WW plants reduced the shoot and taproot weight and their water contents. The nitrate content in the taproots was reduced in the NW and WW plants. The WW plants contained lower total phenol and higher ascorbic acid and sugar contents. These results suggest that the uptake of nutrient minerals at the young growth stage is important for the growth of radish taproot. Nutrient deficiency management can be one of the most effective tools for regulating radish growth and composition.

Hazards of nitrogen fertilizers and ways to reduce nitrate accumulation in crop plants

In modern agriculture, farm produce accumulates a lot of nitrates that can reach toxic levels owing to the unfair use of nitrogen fertilizers, cultural methods, farming policies in multiple areas of the world, thereby increasing concerns about the availability of hygienic food supply and environmental hazards. Over the past few decades, global interest in achieving greater output through intensive fertilization has been a growing trend. The fertilizer based on urea or ammonium mainly yields ammonium, which is then transformed to nitrate through the oxidation process that is biologically mediated. Nitrate tends to accumulate differently in distinct crop plants and distinct components of agricultural commodities based on species, crop variety, genetic history, environmental circumstances, harvest phase, post-harvest storage conditions, agronomic variables, nature, and fertilizer application rate. The current article highlights various factors that could directly or indirectly contribute to the accumulation of nitrates in different parts of crop plants and discusses strategies to minimize the accumulation of nitrates in farm produce, thus ensuring healthy food supply and protecting the environment from the accumulation of nitrates.

Evaluation of the plant growth-promoting activity of Pseudomonas nitroreducens in Arabidopsis thaliana and Lactuca sativa

KEY MESSAGE

Pseudomonas nitroreducens: strain IHB B 13561 (PnIHB) enhances the growth of Arabidopsis thaliana and Lactuca sativa via the stimulation of cell development and nitrate absorption. Plant growth-promoting rhizobacteria (PGPR) enhance plant development through various mechanisms; they improve the uptake of soil resources by plants to greatly promote plant growth. Here, we used Arabidopsis thaliana seedlings and Lactuca sativa to screen the growth enhancement activities of a purified PGPR, Pseudomonas nitroreducens strain IHB B 13561 (PnIHB). When cocultivated with PnIHB, both species of plants exhibited notably improved growth, particularly in regard to biomass. Quantitative reverse transcription polymerase chain reaction analysis indicated high expression levels of the nitrate transporter genes, especially NRT2.1, which plays a major role in the high-affinity nitrate transport system in roots. Moreover, enhanced activity of the cyclin-B1 promoter was observed when wild-type 'Columbia-0' Arabidopsis seedlings were exposed to PnIHB, whereas upregulation of cyclin-B also occurred in the inoculated lettuce seedlings. Overall, these results suggest that PnIHB improves A. thaliana and L. sativa growth via specific pathways involved in the promotion of cell development and enhancement of nitrate uptake.