ИСТИНА

The Impact of Secondary Carotenoids on Plant Optical Properties Alexei Solovchenko1,3 and Anatoly Gitelson2 1Department of Bioengineering, Faculty of Biology, M.V. Lomonosov Moscow State University 1/12 Leninskie Gori, Moscow, Russia 2Faculty of Civil and Environmental Engineering, Israel Institute of Technology, Technion City, Haifa, Israel 3Eurasian Center for Food Security MSU, Moscow, Russia Abstract Carotenoids are accessory pigments ubiquitous in phototroph organisms from single-celled algae to terrestrial plants. These pigments are divided into two groups: one is very well known photosynthetic or primary carotenoids essential for light capture, photoprotection, and integrity of photosynthetic apparatus. The second group is constituted by secondary carotenoids which are not connected to photosynthesis and accumulated under stress and/or during leaf/fruit senescence outside chloroplast thylakoids in dedicated lipid droplets. The secondary carotenoids are believed to serve different aspects of photoprotection although their overall significance is much less understood. We show that accumulation of the secondary carotenoids can exert a considerable contribution and even govern the observed trend of changes in plant optical properties and performance of vegetation indices like PRI reflecting engagement of the carotenoid-based photoprotection. On the examples of broadleaf trees (beech), field crops (corn) and apple fruit we demonstrate that ageing of plant tissues is, in many species, associated with a progressive accumulation of secondary carotenoids. Normally this progress reflects a changeover of the dominant mode of photoprotection from active (based on the operation of energy-dependent mechanisms like xanthophyll cycle) to passive (e.g. optical shielding by lipid droplets rich in secondary carotenoids). We briefly discuss the caveats in the interpretation of the vegetative indexes stemming from accumulation of secondary Car and potential use of these pigments as a sensitive and reliable marker of developmental changes and life cycle progression in plants. Partial financial support of Russian Foundation for Basic Research (project 18-416-680007) is greatly acknowledged.