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ŠUMARSKI LIST 3-4/2022 str. 40     <-- 40 -->        PDF

C. colurna leaves contained mainly quercetin and myricetin (Benov and Georgiev, 1994). Riethmüller et al. (2014) investigated the phenolic compounds and antioxidant activities in different parts of the C. colurna. In parallel to our results, they detected quercetin, kaempferol and myricetin in methanolic leaf extract. Some phenolic compounds such as 3-, 4- and 5-caffeoylquinic acids, caffeoyltartaric acid, p-coumaroyltartaric acid, myricetin 3-rhamnoside, quercetin 3-hexoside, quercetin 3-rhamnoside, kaempferol 3-rhamnoside and derivatives of p-coumaric acid, myricetin and quercetin were identified in the cultivars of C. avellana leaves by HPLC-DAD (Amaral et al., 2005; Oliveira et al., 2007; Amaral et al., 2010).
Water deficiency stress (W2) was applied in June and July having average temperatures as 16.2 ºC and 19.2, respectively. Generally, it was observed that water stress generated by halved irrigation regime (W2) elevated the phenolic constituents in both months, and the highest increase was observed in July due to the higher average temperature. Among the populations, PL was the most affected by water stress, and overall phenolic content was enhanced from 0.70 mg/g to 0.94 mg/g in June. Noticeable increase in individual phenol was obtained with luteolin level (34.4 times) in June in PL population (Table 2 and 3; Fig. 3). A steady increase was monitored with rutin level in OG population and with luteolin level in ER population from June to July with water stress. In addition, halved irrigation regime affected and elevated rutin level significantly in June and July in PL population (Table 2 and 3; Fig. 3).
Enhancements were observed significantly with water stress with most of the tested phenols. For example, rutin increased from 2.77 mg/g to 4.32 mg/g in PL population (56% rise) and from 1.08 mg/g to 1.48 mg/g in OG population (37% rise) in June. Similarly, 2.33-fold increase with rosmarinic acid in SE population in June, and 3-fold increase with apigenin in GF and PL populations in July were observed. Gallic acid showed 2.29 times and 2.00 times increase in OG and SE populations in June, respectively. Caffeic acid was elevated 1.42 times in OG and ME populations in June. Myricetin showed 3-fold rise in ME population in June and 5-fold rise in SE population in July. Kaempferol increased 1.36 times in ME and 1.20 times in OG in June, and 1.62 times in SE and 3.51 times in PL populations in July. Luteolin was ascended 3.03 times in ER and 1.30 times in OG in July (Table 2 and 3; Fig. 3).
Photosystem quantum efficiency (photosynthetic efficiency) in chlorophyll fluorescence measurements (Fv/Fm ratio) were also performed to determine the effect of water deficiency stress on photosystem II in TH leaves. The Fv/Fm ratio has long been regarded as a sensitive indicator of plant photosynthetic performance and as a numerical value in many developed plants is around 0.83. Decreases in this index indicate a decrease in PS II efficiency, i.e. photoinhibition. The main effect of abiotic stress is that PS II becomes inclined to photoinhibition (Rong-hua et al., 2006; Köseoğlu and Doğru, 2021). Overall, drought stress-induced photoinhibition (W2) was observed as a significant reduction in the maximum quantum efficiency (Fv/Fm) of PS II in TH leaves comparing with control (W1) (Fig.3). In June, the Fv/Fm values varied between 0.55-0.82 according to the populations in W1 irrigation, and this value decreased to 0.50-0.78 with W2 irrigation. In July, values between 0.67-0.82 in W1 irrigation decreased to 0.58-0.71 values in W2 treatment (Fig. 3). These results showed that water deficiency created a stress in the trees and it can be interpreted that this stress caused an increase in some phenol levels and populations. Similarly, Galle et al. (2007) determined photosynthetic performance in young pubescent oak (Quercus pubescens) trees during drought stress and reported the decrease in Fv/Fm values in stress-treated trees comparing with control. Wang et al. (2018) created drought stress in young apple tree with less irrigation and showed the decrease in Fv/Fm value to 0.375. However, Fv/Fm ratios in other words photosynthetic performance differed in each population in our study. In connection with this result, Rong-hua et al. (2006) reported that under drought stress in Barley, Fv/Fm values in drought tolerance genotypes were considerably greater than those in drought sensitive genotypes. The lowest Fv/Fm ratio (0.50) was obtained with PL population in June in our study (Fig. 3). The fact that the Fv/Fm value that is an indicator of photosynthetic activity was low in PL population that has the highest phenolic level, showed that this population was the most affected by drought stress. On the other hand, Fv/Fm values of GF population (W1) were higher than other populations. In addition, this population had the lowest overall phenolic content and interestingly, applied water stress in both months (W2) in this population did not cause an increase in phenolic content. This population should be more tolerant to water stress than other populations and able to cope with abiotic stress more easily without giving stress-induced increase in phenolic substances. Similarly, SE population with the second lowest phenolic content had higher Fv/Fm ratios. In SE population, water stress application in June could not increase the phenolic content and even the phenolic content decreased. It can be deduced that SE population is second stress-resistant population after GF population.
Among the tested populations, PL had the highest phenolic content, and their levels enhanced at most with water deficiency stress. Rutin, kaempferol and luteolin were determined as the most abundant phenols in all populations of Turkish hazel leaves and remarkable increases were observed with drought stress in luteolin and rutin levels in PL