Analysis of the effect of chloroplast arrangement on optical properties of green tobacco leaves Barbora Baránková, Dušan Lazár, Jan Nauš ⁎ Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Šlechtitelů 27, 783 71 Olomouc, Czech Republic abstract article info Article history: Received 15 July 2015 Received in revised form 5 November 2015 Accepted 9 December 2015 Available online xxxx There are many studies showing the active optical reaction of a green leaf to the changing surroundings based on chloroplast movement and their rearrangement in plant cells. These studies concentrated mostly on the effect of one feature (leaf type, leaf side or light type) on the leaf optical spectra. We have measured the diffuse reflectance and transmittance spectra of tobacco green leaves in combination of 4 variants: in normal and water infiltrated leaves, in collimated or diffuse incident light, on both the adaxial and abaxial leaf sides, and for the face or side chloroplast arrangement. A Simple Explicitly Non- Linear Empirical model for Leaf Optical Properties (SENLELOP model) is used to theoretically describe, simulate and fit the deviations from the Lambert–Beer's law causing nonlinearity in the measured spectral changes. It is shown that the incident diffuse light is captured by the leaf more effectively than the collimated light. The light incident from the adaxial leaf side is more effectively absorbed than the same light incident from the abaxial leaf side. The air in intercellular spaces of natural leaf increases about twice the beam path and strongly deepens the non-linearity of the absorption process when compared with water infiltrated leaf. The chloroplast arrangement in the palisade cells is reflected in most of the studied differences. The leaf absorbance changed in our case of tobacco leaves up to 30% when the chloroplasts moved from the face to the side position. This change depends strongly on the wavelength and quite slightly on the character of incident light. Further analysis predicts that in practice the effect of chloroplast rearrangement on the reflectance spectra is in dependence on the wavelength of the light about 2–5% in our case of fully developed green leaves but can be higher in some cases. Thus it can affect values of some of the indices used in the remote sensing. © 2015 Elsevier Inc. All rights reserved. Keywords: Diffuse reflectance Diffuse transmittance Absorptance Leaf absorbance Infiltration Chlorophyll fluorescence Collimated light Diffuse light Nonlinearity 1. Introduction A green leaf of higher plants can, to some extent, react and adapt to the changing light conditions. This reaction is aimed to optimize the ab- sorption of light quanta both to maximize the energy utilization in pho- tosynthesis and to avoid harmful over-excitation. The process of this adaptation is rather complex occurring in different time-scales and may cover a change in the leaf position, leaf structure (e.g., swelling), chloroplast movement, pigment composition, the state transitions or energy quenching. We concentrate in this paper on the effect of chloro- plast arrangement on the optical properties of leaves. The ability of leaves to adapt its inner chloroplast arrangement to the light conditions also influences the resulting optical properties of leaves, i.e., the leaf spectra of reflectance, transmittance, absorptance and fluo- rescence. The leaf reflectance is usually the basis of the image detection of a canopy by the spectral or multispectral cameras, both in laboratory and in remote sensing studies. This implies that the detected spectral image can be also influenced by the chloroplast arrangement in leaf cells without changes in leaf structure or chlorophyll content. It can be expected that even the light environment within the canopy (light spec- trum, geometry, intensity) can be influenced by the chloroplast ar- rangement in the individual leaves and leaf layers. This indicates that the knowledge of this phenomenon, including its theoretical descrip- tion, should be taken into account in the remote sensing studies. Our work aims to attract the attention of researchers to the changes in optical spectra of leaves due to changes in chloroplast arrangement in leaf cells. We suggest a simple method of mathematical description and evaluation of these changes. Our work is based on previous original ex- perience showing the effect of chloroplast movement in the signal of chlorophyll fluorescence or in the readings of a chlorophyll meter (Brugnoli & Björkman, 1992; Nauš, Prokopová, Řebíček, & Špundová, 2010). Our study is restricted to the situation on a level of one leaf. The upscale transfer to the level of whole plant or canopy is a matter of further research. 1.1. Optical parameters By optical parameters we mean here the spectra of leaf reflectance, transmittance, absorptance and fluorescence. From this point of view, Remote Sensing of Environment 174 (2016) 181–196 ⁎ Corresponding author. E-mail address: naus@prfnw.upol.cz (J. Nauš). http://dx.doi.org/10.1016/j.rse.2015.12.011 0034-4257/© 2015 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse