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To explore regulated mechanisms of Brassinosteroids-induced chilling tolerance, we studied the involvement of foliar sprayed 24-epibrassinolide (EBR) in the growth, lipid peroxidation, distribution of absorbed energy and excitation energy, chlorophyll fluorescence characteristics and antioxidant defense system of pepper seedlings under chilling stress. We found that low temperature retarded the growth of pepper seedlings, but foliar spray of EBR solution markedly improved the photoinhibition by increasing maximum quantum efficiency of photosystem II (Fv/Fm), the actual photochemical efficiency of photosystem II, photochemical quenching coefficient and the efficiency of excitation capture of open PSII center (Fv'/Fm'). Likewise, EBR increased the fraction of photochemical efficiency (P) and reduced the fraction of antenna heat dissipation (D) and excess energy (E). Low temperature led the increase in end product of lipid peroxidation and the content of H2O2, O2 - and OH-, and it caused the occurrence of oxidative stress. The activities of antioxidative enzymes including superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and contents of ascorbic acid and reduced glutathione were significantly improved by EBR during low temperature stress. The application of EBR also markedly increased the contents of proline, soluble sugar and protein under low temperature. EBR significantly reinforced antioxidant defense system, and it can be reflected through the reduced accumulation of harmful reactive oxygen species and MDA in pepper seedlings. Overall, these results suggest that EBR increases the tolerance of pepper seedlings against chilling stress largely by optimizing distribution of absorbed energy and excitation energy and enhancing antioxidant defense system.
Investigations were carried out to study the responses of canola (Brassica napus) under contrasting temperature regimes (day/night C): 35/30 (high temperature) and 15/10 (low temperature) in comparison with optimal temperature (25/20) at early seedling stage. The results indicated that high temperature inhibited seedling establishment, while low temperature restrained seed germination. Both high and low temperatures showed detrimental effects on seedling growth as revealed by reduced establishment percentage, seedling vigor index, and fresh weight due to accumulated reactive oxygens. The antioxidant enzymes responded to high and low temperature differently. Under high temperature, superoxide dismutase (SOD) and peroxidase (POD) activities reduced, while catalase (CAT) activities increased. Under low temperature, however, SOD activities increased, while POD activities reduced, with CAT activities unchanged. Proline played an important role in temperature stress tolerance and can be used as an indicator for tolerance to unfavorable temperature conditions in canola seedlings. Huayouza 9 showed much stronger tolerance to both high and low temperature compared with other cultivars tested in this study. The full extent of tolerance mechanisms need to be further studied.
Keichousaurus hui is a small pachypleurosaur (Reptilia: Sauropterygia) from the Triassic of China. Many specimens of various growth stages are known, making them ideal for ontogenetic research. We report 22 new specimens from the Middle Triassic of Xingyi (Guizhou, south China), and combined their skeletal measurements with those from 85 published specimens to analyze the ontogenetic trajectory of sexual dimorphism. An Exploratory Factor Analysis suggests that the largest factors behind morphological disparity within the species are body size followed by gender. Sexual dimorphism is most clearly reflected in selected skeletal ratios that are more pronounced in males than in females. We found that the relative length of femur to body size was useful in gender identification, in addition to three ratios that are traditionally used, namely a distal expansion of the humerus relative to its shaft, humerus length relative to body size, and humerus length relative to femur length. Two distinctive patterns exist in allometric changes of these four ratios. The distal expansion of the humerus is exceptional in that it is equally pronounced in juvenile and adult males and therefore must have been fully established during embryonic growth. The other three features are not pronounced at birth size and subsequently become pronounced during postembryonic growth. However, males and females already show different growth trajectories at birth size even in these three. Therefore, the fate of sexually dimorphic features seems to have already been set during embryonic growth in K. hui.
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