# Making Sense of Light: The Use of Optical Spectroscopy Techniques in Plant Sciences and Agriculture
## 4 Current Applications and Future Perspectives
### Other Methods  
Despite the impressive progress in processing multispectral images, which made it possible to indirectly assess a plethora of ecosystem parameters and provided valuable applications in agriculture, the elastic spectroscopy alone is not capable of providing adequate technical solutions to many topical problems of plant sciences. By its nature, the spectra of elastically scattered light--photons that underwent rather simple and relatively weak interaction with matter--lack information about the biological sample state and composition. On frequent occasions, such a lack \"cannot be remedied by any mathematical trickery\" [95], and more complex optical phenomena must be brought into the scene to provide the required data reliability. The introduction of new and improved Raman devices that simplify data collection, along with the possibility of conducting analyses without the need for prior labeling and complicated sample preparation, has turned this spectroscopic technique into a reliable \"solution\" for some of the limitations met by the elastic spectroscopy [45]. Raman produces specific spectral fingerprints, allowing the non-destructive detection and quantitation of several key compounds, which makes it a powerful tool in the monitoring of the physiological status of plants, the assessment of fruit quality, pathologies and ripening [1; 45; 73; 96; 97; 98]. In fact, Raman is another optical spectroscopic technique claimed by precision agriculture, which has the potential for significantly improving the capacity of farming management, quality assessment, detection of biological and/or chemical contamination, contributing to food safety, productivity, and profitability. Similar to other spectroscopic techniques, the information extraction from the spectra acquired from plant tissues requires the use of various machine learning techniques and the mandatory access to spectral databases comprising the standards for the identification of every fingerprint acquired [45; 97; 99]. These spectral libraries, which are becoming more comprehensive and extensive by the day, allow the interpretation of the collected tissues fingerprints in terms of the plant physiological status, the stress factor involved, the fruit ripening stages, and the detection of pathologies and/or disorders. Raman spectroscopy has further been used in the development of high-throughput phenotyping of plants under biotic and abiotic stress [98; 100]. The latter was demonstrated for Coleus (_Plectranthus scutellarioides_) subjected to various abiotic stress conditions [101]. This technique was also used to determine the nitrogen status in _Arabidopsis thaliana_ and two varieties of leafy vegetable crops, namely, Pak Choi (_Brassica rapa_ var. chinensis) and Choy Sum (_Brassica rapa_ var. parachinensis), under different nitrogen soil concentrations [96]. A specific spectral signature was identified for the plant nitrogen status, which can be used in the early diagnosis of its deficiency in plants before the onset of any visible symptoms. Handheld Raman spectrometers that allow a form of laser-induced biochemical fingerprinting of living plants, yield precise access to the plants' physiological responses under field conditions [97] by both farmers and plant researchers. This was demonstrated in a study by [101], where a portable leaf-clip Raman sensor was once again successfully used for the early diagnosis of nitrogen deficiency in _Brassica_ spp. Relative success has been achieved when applying Raman in the quantitation of various compounds, such as pigments and SSC of various fruits and vegetables, namely, tomato, mango, and kiwifruit; the Bruise identification on apples; and the detection of heavy metals contamination in rice, wheat and corn grain [1; 73; 102]. Additionally, it has further been used in the non-invasive assessment of lignin structure, its distribution and cellular level of dissociation, which along with cellulose, is the only non-fossil natural resource providing renewable aryl compounds [103].