Ahmet Korkmaz

Cyclic 3-hydroxymelatonin (3-OHM), a significant metabolite derived from melatonin (MEL) through its interaction with oxygen-containing compounds, is believed to play a crucial role in enhancing plant resistance to various abiotic stresses. Despite its importance, research on 3-OHM remains limited. Therefore, this study aimed to investigate the effects of exogenous 3-OHM treatments on the drought stress tolerance of pepper seedlings during the emergence phase. The application of 3-OHM to seeds at various concentrations (0, 10, 50, and 100 µM) notably improved seedling emergence performance under drought conditions compared to untreated controls. Furthermore, 3-OHM treatments significantly reduced oxidative stress markers such as hydrogen peroxide (H₂O₂) and thiobarbituric acid reactive substances (TBARS), while simultaneously enhancing the activities of key antioxidant enzymes including peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT). Additionally, seedling proline and total chlorophyll contents increased significantly by 3-OHM application. Among the concentrations tested, 50 µM 3-OHM consistently showed the most pronounced beneficial effects across multiple parameters. These results underscore the potential utility of 3-OHM as a natural bioactive compound to mitigate the detrimental impacts of abiotic stress in agricultural crops. To further elucidate the physiological mechanisms and confirm the efficacy of 3-OHM, future studies should focus on comparative analyses with MEL, employing the optimal 3-OHM concentration identified herein.

Although the antioxidant role of melatonin in stress mitigation is well established, its multifunctionality may support plant tolerance to drought through additional mechanisms. This study aimed to evaluate melatonin’s contribution to both antioxidant defence and methylglyoxal (MG) detoxification—a harmful compound that disrupts cellular balance under drought stress. The glyoxalase pathway, which is aided by glutathione, plays a pivotal role in MG detoxification. Therefore, we examined the impact of both endogenous and exogenous melatonin on this system. Two pepper genotypes differing in drought tolerance and endogenous melatonin levels were exposed to 12 days of drought following a 5 µM melatonin treatment. The drought-tolerant genotype, characterized by higher levels of endogenous melatonin, exhibited more efficient MG detoxification through increased glutathione and glyoxalase activities, reduced membrane damage and enhanced antioxidant capacity. Exogenous melatonin further mitigated the effects of drought by reducing MG accumulation and stimulating antioxidant and glyoxalase enzymes. Overall, both endogenous and applied melatonin enhances drought tolerance in pepper by activating antioxidant defences and the glyoxalase pathway.

Although the diurnal fluctuations of melatonin (Mel) content in plants and its role in abiotic and biotic stress tolerance are well-documented, little is known about its changes within seeds and its potential effects on seed viability or the aging process. This study aimed to determine how artificial aging, induced by a controlled deterioration test, affects the Mel and tryptophan (Trp) content and seed viability. Furthermore, the study evaluated the effects of Mel and Trp applications on mitigating the impacts of aging in artificially aged seeds. Tomato seeds treated with 250 µM Mel and Trp were artificially aged for up to 8 days through controlled deterioration test after which Mel and Trp changes during ageing and the effect of treatments on seed viability and germination performance was determined. Seeds were also treated with Mel and Trp following artificial ageing in order to determine the effects of Mel and Trp on aged seeds. The positive effects of Mel and Trp applications on seed viability and vigor were particularly evident during and after artificial aging, compared to control seeds. It was observed that in control seeds subjected to controlled deterioration test, Mel and Trp contents exhibited an opposite trend. Applications of Mel and its precursor Trp, before and after artificial aging, significantly slowed down the aging process or alleviated the adverse effects of aging by protecting membrane structures against peroxidation and the accumulation of malondialdehyde (MDA) and H2O2. Moreover, indicators of seed deterioration such as electrical conductivity, MDA, and H2O2 contents were significantly reduced compared to untreated seeds, while the activities of antioxidant enzymes were boosted. In conclusion, the importance of Mel and Trp applications in preserving seed viability, minimizing storage losses, and slowing seed aging has been demonstrated, suggesting practical applications, particularly in preserving seeds of endangered species or valuable breeding materials.

Bu çalışma, farklı dalga boylarına sahip led lambalar kullanılarak oluşturulan aydınlatma ortamlarının domates fidelerinin kaliteleri üzerine olan etkilerinin araştırılması ve fide üreticilerinin teslimatlarında herhangi bir sebeple meydana gelebilecek gecikmeler olması durumunda fidelerde boy ve kalite kontrolünün sağlanarak üreticilerin bu sıkıntılarına bir çözüm bulmak amacıyla yürütülmüştür. Bu amaçla öncelikle iklim odasında aynı ışık yoğunluğuna sahip farklı dalga boylarında (kırmızı, mavi, yeşil, beyaz-günışığı karışımı-kontrol) led lambalar altında dikim aşamasından itibaren “Ferguson F1” domates çeşidine ait fideler 10 gün süre ile yetiştirilmiştir. Daha sonra domates fideleri, boy uzamasını baskılamada etkili olduğu belirlenen mavi ışığın farklı oranlarda (%100, %50, %25 ve %12.5) kontrol olarak kullanılan beyaz-günışığı karışımı lambalara eklenmesiyle elde edilen ışık koşullarına maruz bırakılmıştır. Son olarak da farklı oranlarda mavi ışığın uzun dönemdeki etkilerinin kalıcılığını ortaya koyabilmek amacıyla fideler tekrar beyaz-günışığı koşullarına maruz bırakılmıştır. Fide aşamasında kullanılan farklı dalga boyları arasından domates fidelerinin gelişimini baskılayan dalga boyunun mavi ışık olduğu belirlenmiştir. Ayrıca, bitki gelişimini teşvik eden ve fide boyunda artışlara neden olan ışığın ise kırmızı ışık olduğu ortaya konmuştur. Farklı oranlarda mavi ışık koşulları altında yetiştirilen domates fidelerinde mavi ışık oranı azaldıkça bitki yaş ağırlığında ve bitki boyunda önemli seviyede artışlar elde edilmiştir. Farklı oranlardaki mavi ışığın fide kalitesi üzerine uzun süreli etkisine bakıldığında uygulama sonrası kontrol aydınlatma koşullarına alınan domates fidelerinin kalitesi üzerinde mavi ışığın etkisinin geçici olduğu ve fidelerde büyümenin devam ettiği görülmüştür. Bu sonuçlar fide boyunun baskılanmasında %100 mavi ışığın kullanılabileceğini ve mavi ışığın etkisinin hazır fide yetiştiriciliğinde kullanılan kimyasal maddeler gibi kalıcı olmadığını göstermiştir.

The presence of melatonin, a known animal hormone, has been confirmed in many evolutionary distant organisms, including higher plants. It is known that melatonin increases tolerance to stress factors as a wide spectrum antioxidant. Tolerant genotypes have generally higher melatonin content than sensitive ones, and exposure to stressful conditions is known to increase endogenous melatonin levels. However, endogenous melatonin levels in seeds have never been used to select genotypes tolerant to abiotic stresses. Thus, in this study, the existence of possible relationship between seed melatonin levels of 28 pepper (Capsicum annuum L.) genotypes and their germination and emergence performance under chilling conditions (15°C) was investigated. The results indicated that these parameters were much better for pepper genotypes with higher seed melatonin contents while those having less than 2 ng g−1 additionally exhibited elevated levels of MDA and H2O2 but lower antioxidant enzyme activities. Thus, a positive relationship between seed melatonin content and chilling stress tolerance has been shown, suggesting a possible use of endogenous melatonin levels as a criterion in selecting chilling stress tolerant varieties. To save considerable time, money and labour, it is recommended that genotypes with lower melatonin contents are excluded from breeding programmes that aim to develop new stress tolerant genotypes.

Bugün varlığı hemen hemen tüm canlı organizmalarda kanıtlanan bir molekül olan melatonin (N-asetil-5-methoksitriptamin), ilk olarak 1958 yılında sığır beyin üstü bezinden izole edilen bir indolamindir. Son zamanlarda bitkisel bir hormon olarak kabul edilmesinin yanında reaktif oksijen ve azot türlerini ortamdan uzaklaştırma özelliğine sahip olmasından dolayı geniş spektrumlu antioksidan olarak bilinmektedir. Bitkilerde fotoperyodik düzenleyici veya 24 saatlik ritim düzenleyici olarak görev aldığı ifade edilen bu molekülün hayvanlarda ve insanlarda da günlük ve yıllık ritmi kontrol ettiği yapılan yoğun çalışmalar sonucunda bildirilmiştir. Ayrıca melatoninin türe göre değişmekle beraber miktarının özellikle gece veya karanlıkta arttığı ve bazı bitkilerde gün içerisinde ikince kez pik yaptığı da araştırmalar sonucu ortaya konmuştur. Melatoninin bitkilerin ve tohumların yaşlanma metabolizmasında sahip olduğu rol ise tam olarak anlaşılmış değildir. Ancak son araştırmalar melatoninin yaşlanma üzerine olumlu etkisinin, yaşlanmaya neden olan ve yaşlanmayı geciktiren fitohormonların etkisi ile yakından ilişkili olduğunu göstermiştir. Bu derlemede bitki dokularındaki melatoninin gün ve yıl içerisindeki değişimi ve yaşlanma üzerine etkisi hakkında detaylı bilgi verilecektir.

The purpose of this study was to explore the possibilities of improving chilling stress tolerance of eggplant seedlings through exogenous melatonin (MEL) application. Eggplant (Hadrian F1) seedlings were treated with various concentrations (0, 1, 5 or 25 μM) of MEL via soil drench after which they were subjected to chilling stress at 5°C/10°C (night/day) for 3 days. Following stress imposition, the efficacy of MEL applications on enhancing chilling stress tolerance was determined by several physical and physiological measurements and biochemical analyses. The results demonstrated that exogenous application of MEL alleviated the adverse effects of chilling stress in eggplant seedlings. Among the MEL concentrations tested, 5 µM was determined as the most effective concentration since antioxidant enzyme (CAT, POX and APOX) and photosynthetic activities increased while visual and membrane damage decreased in 5 µM MEL-treated seedlings. Also, these results are the first experimental evidence that exogenous application of MEL could improve chilling stress tolerance in eggplant, but further detailed studies are necessary to better understand the mechanism in acquiring chilling tolerance.