Responses of canola (Brassica napus L.) cultivars under contrasting temperature regimes during early seedling growth stage as revealed by multiple physiological criteria

Investigations were carried out to study the responses of canola (Brassica napus) under contrasting temperature regimes (day/night degrees 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.