Majid NABIPOUR, Mousa MESKARBASHEE, Mahroo Mojtabaie ZMANI

Çiçeklenme Sonrası Sıcaklık Stresinin Buğday Çeşitlerinin PSII Fotokimyasal Etkinliği ile Antioksidan Aktivitesine Etkisi

Bu çalışmanın amacı çiçeklenme sonrası sıcaklık stresinin buğday çeşitlerinin fotosistem II (PSII) ile askorbat peroksidaz ve katalaz enzim aktivitelerine etkisini belirlemektir. Dört ekmeklik buğday çeşidine çiçeklenmeden 7 gün sonar başlayıp olgunluğa kadar devam eden sıcaklık stresi uygulanmış, control olarak da sıcaklık stresi uygulanmayan bir grup oluşturulmuştur. Sıcaklık stresi klorozun hızlanmasına neden olmuş, elektron taşınım etkinliğini azaltmış ve malondialdehit konsantrasyonunu artırmış ancak duyarlılık düzeyi çeşitlere göre farklılık göstermiştir. Sıcaklık stresinin 10. gününde çeşitlere bağlı olarak floresans parametrelerindeki azalma kontrole göre Fv/Fm için % 6.9-18.9, ΦPSII için % 9-21 ve F’v/F’m için ise % 8.3-19.4 arasında değişmiştir. Sıcaklık stresinin başlmasıyla birlikte katalaz aktivitesi artış göstermiştir. Ancak sıcaklık stresi uygulmasından 10 gün sonra katalaz aktivitesi Chamran ve Aflak çeşitlerinde sırasıyla % 32 ve 45 oranında artmış, Dez çeşidinde değişmemiş ve Darab2 çeşidinde ise % 22 oranında azalmıştır. Askorbat peroksidaz aktivitesi hem kontrol grubu hem de sıcaklık stresi uygulanan bitkilerde azalmış ancak azalma sıcaklık stresi uygulananlarda daha fazla olmuştur. En yüksek enzimatik aktivite sıcaklık stresi uygulanan Chamran çeşidinde gözlenirken Darab ve Dez çeşitleri en düşük enzim aktivitesine sahip olmuşlardır. Klorofil floresans paramtresi ile klorofil indeksi malondialdehit düzeyleri ile önemli negative korelasyon gösterirken antioksidan aktivitesi ile önemli pozitif korelasyon göstermiştir.

Effects of Heat Stress after Anthesis on PSII Photochemical Efficiency and the Antioxidant Activity of Wheat Cultivars

This study was conducted to investigate the effects of heat stress after anthesis on the performance of Photosystem II (PSII) and the enzymatic activity of catalase and ascorbate peroxidase. Two treatments-normal and heat stress-were conducted on four bread wheat cultivars from 7 days after anthesis until maturity. Heat stress led to an acceleration of chlorosis, reduced the efficiency of electron transfer and increased concentrations of malondialdehyde; however, the level of susceptibility varied depending on the cultivars. On the 10th day of heat stress, reductions in fluorescence parameters, depending on the cultivar, were 6.9 to 18.9% for Fv/Fm, 9 to 21% for ΦPSII and 8.3 to 19.4% for F’v/F’m compared to normal conditions. Catalase activity increased after initial exposure to heat stress. However, after 10 days of treatment, catalase activity increased in the Chamran and Aflak cultivars by 32% and 45%, respectively, but it did not change in the Dez cultivar and decreased 22% in Darab2. Ascorbate peroxidase activity decreased in two treatments, while the amount of reduction in heat stress treatment was more than the normal treatment. The highest levels of enzymatic activity were observed in Chamran under heat stress conditions, whereas Darab2 and Dez showed the lowest activity of the enzymes. Chlorophyll fluorescence parameters and chlorophyll index had a significant negative correlation with the levels of malondialdehyde; however, they had a significant positive correlation with the antioxidant activity.

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