Nitrogen (N) plays a key role in the plant life cycle. It is the main plant mineral nutrient needed for chlorophyll production and other plant cell components (proteins, nucleic acids, amino acids). Crop yield is affected by plant N status. Thus, the optimization of nitrogen fertilization has become the object of intense research due to its environmental and economic impact. This article focuses on reviewing current methods and techniques used to determine plant N status. Kjeldahl digestion and Dumas combustion have been used as reference methods for N determination in plants, but they are destructive and time consuming. By using spectroradiometers, reflectometers, imagery from satellite sensors and digital cameras, optical properties have been measured to estimate N in plants, such as crop canopy reflectance, leaf transmittance, chlorophyll and polyphenol fluorescence. High correlation has been found between optical parameters and plant N status, and those techniques are not destructive. However, some drawbacks include chlorophyll saturation, atmospheric and soil interference, and the high cost of instruments. Electrical properties of plant tissue have been used to estimate quality in fruits, and water content in plants, as well as nutrient deficiency, which suggests that they have potential for use in plant N determination.

Bioactive compounds (e.g., flavonoids, phenolics acids, alkaloids and carotenoids) are commercially-valued products, due to their wide array of applications in the medical, pharmacological, cosmetic, agriculture and food industry. A strategy applied to increase or enhancing bioactive compounds production in plants is controlled elicitation. In recent years, many researchers have studied the role of nanoparticles (NPs) as a novel elicitor for the biosynthesis of bioactive compounds shown that the NPs could affect the plant’s secondary metabolism in plant and culture systems. In this sense, recent studies have highlighted the potential applications of nanotechnology in crop production by improving the nutraceutical and nutritional quality of plants. In this review, we present studies about the application of NPs to enhance the production of bioactive plant metabolites. The aforementioned studies in ex vitro as in vitro, in addition to the effect of post-harvest by NPs application.

Over time plants developed complex mechanisms in order to adapt themselves to the environment. Plant innate immunity is one of the most important mechanisms for the environmental adaptation. A myriad of secondary metabolites with nutraceutical features are produced by the plant immune system in order to get adaptation to new environments that provoke stress (stressors). Hormesis is a phenomenon by which a stressor (i.e toxins, herbicides, etc) stimulates the cellular stress response, including secondary metabolites production, in order to help organisms to establish adaptive responses. Hormetins of biotic and abiotic origin (ie. biostimulants), in certain doses might enhance plant performance, however in excessive doses they are commonly deleterious. Biostimulants of biotic origin are called “elicitors” that have widely been studied as inducers of plant tolerance to biotic and abiotic stresses. The plant response toward elicitors is reminiscent of hormetic responses toward toxins in several organisms. Thus, controlled management of hormetic responses in plants using biostimulants of biotic origin (elicitors) is expected to be an important tool to increase nutraceutical quality of plant food and trying to minimize negative effects on yields. The aim of this review is to analyze the potential for agriculture that the use of biostimulants of biotic origin could have in the management of the plant hormesis. The use of new biostimulants in crop production is also discussed.