Analysis of the effect of chloroplast arrangement on optical properties of green tobacco leaves

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.