# Measurement of Visible Radiation through a _Sansevieria cylindrica_-Based \"Living Sensor\"
## 2 Materials and Methods  
_Sansevieria cylindrica_, commonly named _Sansevieria_, belonging to the genus _Dracaena_ (family _Asparagaceae_), is also known as _Dracaena angolensis_, and it is a _Crassulaceae_ plant originating from subtropical African regions [35]. During its growing season, _Sansevieria_ requires moderate amount of water, if given the correct illumination, being a drought-tolerant species. In general, _Crassulaceae_ are drought-resistant plants, in that all their tissuesmay be considered water-storing tissues, characterized by a typical carbon fixation pathway, well known as crassulacean acid metabolism (CAM), which evolved in plants which have adapted to arid conditions as they are able to photosynthesize during the day, keeping closed their stomata and exchanging gases only during the night [36]. _Sansveieria cylindrica_ was the plant used in this study about the measurement of Vis-light. _Sansveieria asparagaceae_ was also implemented and adapted as a plant microbial fuel cell (PMFC) power cell with an energy harvester circuit to supply direct current energy output power to the sensor nodes to collect and monitor the information for environmental protection, urban planning, and risk prevention [37]. Therefore, the choice of this plant is due to its characteristics as care system, which allows easy cultivation, both indoors and outdoors. Moreover, for its physiological characteristics, _Sansveieria cylindrica_ may be a suitable prototype sensor for monitoring several indoor environmental changes such as Vis-light intensity. Focusing our attention on the proposed approach, recently, _Dimorphothea ecklonis_ was successfully used as \"living sensor\" for UV-A radiation measurements, and the mechanism hypothesis was linked to the photoexcitation of cryptochromes by processes involving electron transfer and flavin reduction [34; 38]. It is well-known that alteration in the influx and/or the efflux of metabolites from the epigeal part of the plant to the root tip can have cascading effects on the root system architecture, and hence on root rhizdeposition [39], thus leading to a change in the net efflux of root exudates in the rhizosphere, which is the soil fraction directly influenced by roots and associated with soil micro-organisms [40]. Root rhizodeposition may strongly influence the physiochemical properties of the rhizosphere, putatively inducing a change in the soil redox potential [41]. The compounds in root rhizodeposition, especially sugars and organic acids, may differ depending on the type of plant metabolism [42]. The qualitative composition of root exudates in CAM plants showed the occurrence of high amounts of succinate, malate, and citrate, organic acids which can affect the electrochemical properties in the rhizosphere [43; 44]. Moreover, using three different plant prototypes with different metabolisms (C3, C4, and CAM) to determine the output power of the PMFCs, CAM plant registered the highest maximum power density among plants, at 30.39 mW/m\({}^{2}\)[45]. CAM plants, as they are drought-resistant, are able to generate rhizodeposition even in dry soil conditions [46]. In different environmental light conditions, plants may modulate their primary metabolism by regulating photosynthesis [46]. Plant carbon allocation and distribution in their tissues are regulated by the source-sink dynamics, and soil micro-organisms should also be considered as a strong sink of plant photosynthates, thereby promoting root exudation [47; 48; 46]. A hypothesis to explain the obtained results in this study may be linked to the regulation of plant photosynthate flux from the epigeal to the hypogeal part of the plant in response to light modulation, thus inducing root exudate production, which may modify the soil redox potential, and therefore the measurable signal among cathode and anode (Figure 1).