Abstract
Nitrogen is essential for the plant because it is used for the production of chlorophyll, proteins, nucleic acids, amino acids, and other cellular compounds; nitrogen is available in two forms: ammonium and nitrate. Several tools have been used to quantify nitrates in plants such as the Kjeldahl method and Dumas combustion digestion; however, they are destructive and long time-consuming methods. To solve these disadvantages, methods such as selective electrodes, optical sensors, reflectometers, and images based sensors have been developed; nonetheless, all these techniques show interference when carrying out measurements. Currently, biosensors based on genetic constructions, based on the response of promoter gene fused to Gene Fluorescent Protein (GFP), are gaining popularity, because they improve the accuracy of measurements of nitrate by avoiding the interference of carriers ion, high salt conditions, and other factors. The present review shows the different methods to quantify the nitrogen in plants; later, a biosensors perspective is presented, mainly focused on biosensors based on organism genetically modified. The review presents a list of promoter and reporter genes that could be used to develop different kind of sensors, and a perspective of sensors to measure quantitatively the nitrogen is presented.
Highlights
Nitrogen is the most important nutrient in plants because it is required for chlorophyll production and other cellular compounds [1]
The nitrogen is disposable in two forms that are ready to be used by the plants: ammonium (NH4+) and nitrates (NO3−) [2]
Rapid methods have been developed to determine the quantity of NO3−; one of them is through nitrate-selective electrodes; this has presented interferences caused by the presence of other acceptor ions [8]
Summary
Nitrogen is the most important nutrient in plants because it is required for chlorophyll production and other cellular compounds (proteins, nucleic acids, and amino acids) [1]. The methods commonly employed, such as Kjeldahl Digestion and Dumas combustion, are destructives and take long time for the analysis [7] To avoid these disadvantages, rapid methods have been developed to determine the quantity of NO3−; one of them is through nitrate-selective electrodes; this has presented interferences caused by the presence of other acceptor ions [8]. There are other methods based on optics principles to measure nitrates like radiometers, reflectometers, and sensors based on satellite images (dozel reflectance), leaf transmittance, and chlorophyll and fluorescence polyphenols [9] These methods have high correlations between the optical parameters and nitrogen content of the plants and have the advantage of being nondestructive [7]; there are some drawbacks such as chlorophyll saturation, atmospheric interferences, and the high cost of the instruments. The responses to this kind of biosensors are being employed due to its sensibility and versatility [13], being the sensitivity of the fluorescence proportional to the concentration of extracellular nitrate [10]; biosensors using GFP take long time to be prepared; developing this kind of devices takes a long time; so far, there are no suitable electronic devices for this task to be applied in crops
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