The Effect of drought stress on seed germination chlorophyll, proline and antioxidant enzyme activity in two cultivars of rapeseed (Brassica napus L.)

Drought is one of the most important environmental stresses and occurs for several reasons, including low rainfall, salinity, high and low temperatures, and high intensity of light. Drought stress causes changes in the physiological, morphological, biochemical, and molecular traits in plants. In Iran, many regions suffer from water stress. Moreover, rapeseed is one of the best crops for rotation with wheat. So, and the culture of rapeseed has been increasing recently in Iran. However, rapeseed often suffers from many stresses, such as salinity, cold and drought, which cause great yield loss every year. Since the rapeseed is an economical crop in Iran and drought stress is a limiting factor for crop production, this study was performed to compare some drought resistance mechanisms in sensitive and tolerent cultivars of rapeseed.

This research was designed to identify some drought resistance mechanisms in two cultivars of rapeseed. (Sensitive and tolerant) in germination (with five drought levels) and vegetative stages (zero, low, moderate and severe levels). Polyethylene glycol 6000 (PEG) was used to induced drought. Finally, pigment photosynthesis, proline content, and activity of guaiacol peroxidase was determined. The data obtained undergone a two-way analysis of variance and the mean differences were compared and tested by Duncan test using SPSS v. 2016 software from three replications. Differences at P≤0.05 were considered significant.

In the low level of drought stress, the significant difference was not observed between cultivars at the germination stage. However, the results showed that with increasing drought, germination percentage and shoot length decreased so that it reached zero at the lowest water potential, while root length increased at -0.14 MPa osmotic potential and then decreased at the lower water potential. In the second stage of experiments, the amount of photosynthetic pigments enhanced with reduction of water potential and it was more under moderate and severe stress in sensitive and tolerant cultivar, respectively. Also, the proline content increased to the level of moderate drought stress, which was significantly higher in the tolerant cultivar than the sensitive cultivar. Except for severe drought, the activity of guaiacol peroxidase enzyme was not statistically significant between other treatments and it was more in the roots of tolerant plants compared to sensitive plants. In general, due to the high amount of photosynthetic pigments and proline and guaiacol peroxidase activity in resistant cultivars, it can be suggested that increased efficiency of photosynthesis under stress as a result of more photosynthetic pigments, effective removal of ROS due to high activity of guaiacol peroxidase enzyme and higher compatibility as a result of osmotic regulation by proline accumulation, are part of the mechanisms of coping with dehydration in tolerant canola cultivars.

The results of this study showed that just germination factors could not confirm the sensitivity and resistance of rapeseed cultivars, and more experiments in the hydroponic culture medium is a better way to identify resistant cultivar.