Heat Stress In Kentucky Bluegrass

The study was aimed to investigate the differential responses of antioxidant enzyme system to varied heat stresses in Kentucky bluegrass cultivars with various heat-tolerances. Three species of Kentucky bluegrass heat-tolerant’Thermal Blue’, heat-moderate’Utmost’ and heat-sensitive ’Excursion’ were exposed to slight heat stresses30℃/25℃(day/night),35℃/30℃(day/night) and severe heat stresses40℃/35℃(day/night),45℃/40℃(day/night). And enzyme activities and isozyme profiles of superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidases (APX) and glulathione reductase (GR) were measured. The results of treatments with slight heat stresses showed that significantly higher SOD activities were detected in three cultivars and ’Utmost’ and ’Excursion’ had higher SOD activities than ’Thermal Blue’ during heat stress. The isozymes of SOD didn’t change significantly, whereas the intensitiesof ’Thermal Blue’ was lower than ’Utmost’ and ’Excursion’. With slight heat stresses, POD activities were significantly increased compared with untreated (Od) in three cultivars except in’Excursion’under30℃/25℃and the POD activities in ’Thermal Blue’were significantly higher than in’Utmost’and’Excursion’during heat stress. Increaseing intensities of POD isozymes were found in three cultivars and the POD isozymes were significantly intensive in ’Thermal Blue’ than in ’Utmost’ and ’Excursion’after heat stress. No significant changes of CAT activities were observed in ’Thermal Blue’, nevertheless, significant decreases in ’Utmost’ and ’Excursion’ when suffered with both slight high temperatures. CAT isozymes were induced in three cultivars and’Thermal Blue’had higher isozymes intensities than’Utmost’and ’Excursion’with the specific isozyme C2(Rf=0.62). Within three cultivars, the APX activities remained unchanged and APX isozyme A3(Rf=0.25) was induced, A5(Rf=0.53) and A6(Rf=0.58) were increased when treated by30℃/25℃. But APX activities were significantly increased at20d of35℃/30℃treatment and the intensities of APX isozymes maintained unchanged in three cultivars. The APX activities in ’Thermal Blue’were lower than ’Utmost’ and ’Thermal’ before and after two heat stresses. Both high temperatures significantly increased the GR activities of three cultivars compared with Od and higher GR activities were detected in’Utmost’and ’Excursion’than in’Thermal Blue’before and after heat stresses. No significant changes were observed among three cultivars during heat stresses. However, the isozymes of GR were induced at30℃/25℃, but increased at35℃/30℃compared with Od.With severe heat stress40℃/35℃, the SOD activity was declined first (before1d) and then increased in’Thermal Blue", but increased firstly and then decreased and increased again in ’Utmos’ and ’Excursion’. The intensities of SOD isozymes were also declined first (before3d) and then increased in three cultivars, and the intensities were stronger in’Thermal Blue’and’Utmost’than in’Excursion’. Under45℃/40℃, the SOD activities in three cultivars were increased before Id and then decreased. No significant differences were detected among cultivars. There were no significant changes during heat stress and no significant differences in SOD isozymes among cultivars. With40℃/35℃treatments, POD activities of three cultivars changed with the same tendency, which was significantly increased at Id and decreased gradually at2-4d. The activities of SOD in "Thermal Blue’were higher than’Utmost" and’Excursion" during heat stress except at Id. And the POD isozymes of three cultivars were declined in total and the intensities of P8-P10(Rf=0.60,0.65,0.70) were higher in’Thermal Blue’ than in ’Utmost’ and ’Excursion’during40℃/35℃. Under45℃/40℃, POD activities were descending at the beginning and then rising, whereas remained unchanged in’Utmost’and’Excursion’ The intensities of POD were stronger in’Thermal Blue’than in’Utmost’and’Excursion’ during45℃/40℃. No significant changes of CAT activities were observed in’Thermal Blue’and’Excursion’, but significant increasements in’Utmost’when treated by40℃/35℃. The CAT activities of three cultivars were significantly decreased after45℃/40℃treatment, and the highest descending extent was found in’Excursion’. With the40℃/35℃treatment, the intensities of CAT isozymes were strengthened, whereas no clear changes were observed under45℃/40℃in three cultivars. The intensities of CAT isozymes were stronger in’Thermal Blue’than in’Utmost’and ’Excursion’ under40℃/35℃and45℃/40℃stresses. The APX activities of three cultivars were elevated gradually and then declined quickly, with significant increasement in ’Thermal Blue’ and no difference in’Utmost’and’Excursion’at4d when treated by40℃/35℃. Under45℃/40℃, no significant changes were detected in APX activities of three cultivars. The APX activities in ’Thermal Blue’ were increased firstly, declined secondly and declined at last and exactly the opposite tendency in ’Utmost’ and ’Excursion’. The isozymes of APX in ’Thermal Blue’ were enhanced during40℃/35℃and45℃/40℃treatments and higher intensities were observed than ’Utmost’ and ’Excursion’ thanks to the specific isozyme A5(Rf=0.53), in which the APX isozymes were unchanged during heat stress. With40℃/35℃, the GR activities in three cultivars were all significantly increased at4d and no significant difference among cultivars. Under45℃/40℃treatment, the GR activities in three cultivars were significantly decreased at2d and significantly higher in’Utmost’ than in ’Thermal Blue’ and ’Excursion’. The intensities of GR isozymes were weakened in three cultivars when treated by40℃/35℃and no clear differences among cultivars. Under45℃/40℃, the GR isozymes of three cultivars were enhanced before Id and then declined at2d. And the intensities of GR in’Utmost’were stronger than in’Thermal Blue’ and ’Excursion’.