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ŠUMARSKI LIST 3-4/2022 str. 34     <-- 34 -->        PDF

affects the quantum efficiency (Fv/Fm) of photosystem II activity through chlorophyll fluorescence technique in hazelnut leaves. Generally, Fv/Fm value decreased with water deficiency. This study showed that water deficiency stress generally caused an increase in phenolic constituents in Turkish Hazel leaves and they may be proper natural sources of phenolic constituents with abiotic stress applications in pharmaceutical and food industry.
Key words: Corylus colurna L., quantum efficiency, phenol, Turkish Hazelnut, water deficiency
Genus Corylus belonging to Betulaceae family has three species (Corylus avellana L., Corylus maxima Mill. and Corylus colurna L.) growing naturally in Turkey (Davis, 1982). C. colurna known as Turkish Hazel tree spreads over a wide area from Balkans (Serbia, Bulgaria and Romania), northwest and west Caucasus, north and northwest of Iran, east coast of the Caspian Sea, Afghanistan, Pakistan and the Himalayan Mountains to China. In Anatolia, the most common area is the Northwest Anatolian forests (Polat, 2014). It is also known as Turkish Hazelnut, Turkish Filbert, Tree Nut, Bear Hazelnut, Balkan Hazelnut, Rock Hazelnut Gökbulak Hazelnut and Budağan Hazelnut (Everett, 1988; Polat, 2014). It is the largest hazel species, reaching a height of 35 m and a trunk diameter of up to 1.5 m. It prefers calcareous, well-drained soils (Korkut et al., 2008). It is a species that can be expanded in appropriate places in afforestation and erosion control studies due to its low habitat demand (Arslan, 2005). While it was previously preferred only as a rootstock for cultivated hazelnut varieties for landscape purposes, today it is preferred by hazelnut producers due to its single-stem nature and the low cost of culture in other hazelnut species. As it is a fruity species, it forms the food of wildlife and contributes to biodiversity. Its fruits can be consumed directly as well as used in confectionery (Arslan, 2006). The leaves of Corylus species have been used in folk medicine in the treatment of eczema, rash, swelling, phlebitis, varicose veins and haemorrhoidal symptoms (Riethmüller et al., 2016). C. colurna leaves have been recorded to possess antibacterial activity against Gram-positive and -negative bacteria (Ceylan et al., 2013) and moderate to high antioxidant activity (Riethmüller et al., 2016). C. colurna leaves contain hydroxycinnamic acid derivatives, flavonoid derivatives and diarylheptanoids like quercetin, myricetin, 1-caffeoylquinic acid, 1,3-dicaffeoylquinic acid, catechin and kaempferol (Benov and Georgiev, 1994; Riethmüller et al., 2014; 2016). Benov and Georgiev (1994) isolated mixture of flavonoids from C. colurna leaves and reported strong antioxidant activity. Riethmüller et al. (2014) showed that phenolics in the leaves, bark, catkins and involucre of C. colurna had strong antioxidant activity. Especially, catkins of C. colurna displayed the highest antioxidant capacity, followed by the bark extracts. The catkins had the richest in total polyphenols, tannins, and flavonoids. Riethmüller et al. (2016) indicated that ethyl acetate and methanol extract of C. colurna leaves displayed moderate to high antioxidant activity that may be because of antagonistic interaction between the antioxidant components.
Drought, high temperature, salinity, heavy metals, UV radiation and nutritional insufficiency are examples of abiotic stressors that can increase the generation and accumulation of reactive oxygen species (ROS) in plants. Plants increase the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) to combat these oxidative stresses. They also produce more low-molecular-mass antioxidants such as phenolic compounds, α-tocopherol, ascorbate, and glutathione as non-enzymatic antioxidant activity (Selmar and Kleinwächter, 2013). The major enzyme in phenol synthesis is phenylalanine ammonia lyase (PAL) that is found in higher plants as a secondary metabolic pathway and it is a defense system in plants that is involved in the production of the phenolic compounds. Plants accumulate phenolic compounds in their tissues as an adaptive response to adverse environmental conditions and play a key role in the regulation of various environmental stresses (Thakur et al., 2019; Ulgen et al., 2021). Today, hazelnut tree leaf, which is a by-product of hazelnut harvest, is seen as a potential natural source of antioxidants (Amaral et al., 2010). During the processing of food and agricultural products, by-products rich in phenolics, which can be natural antioxidant sources, can be recycled. Studies are ongoing to extract and produce adequate amounts of natural antioxidants from most of these sources (Balasundram et al., 2006).
Changes in photosynthetic activity are considered as a stress sensor in advanced plants. Currently, the most modern and reliable technique for measuring photosynthetic activity is chlorophyll a fluorescence to reveal the effect of abiotic stress on photosystem (PS) II activity (Köseoğlu and Doğru, 2021). Genotypes that are drought tolerant under