| Rape is an important oil crop in China,which can be used to produce high quality edible vegetable oil.At present,Brassica napus L.is the main planting species.However,seasonal drought often occurs in main rape producing areas in China,resulting in poor seedling,slow growth and decreased yield of rape.Therefore,the study on the response mechanism of B.napus under drought stress is of great significance for the exploration of drought-tolerant genes and the breeding of drought-tolerant cultivars in B.napus.In this study,four B.napus varieties(Bn5-001,Darmor,ZS9 and ZS11)were selected as research meterials,and the drought stress response of seedling leaves was mainly analyzed.The physiological indicators of drought response,such as drought survival rate,water loss rate from detached leaves,relative water content of leaves and leaf area size,showed that Bn5-001 had a relatively obvious drought tolerance phenotype.Cytological analysis of the four B.napus leaves showed that Bn5-001 leaves had less epidermal cells and density.The density of pavement cells and stomatal were negatively correlated with drought tolerance under drought stress in the four varieties.The results showed that the development of pavement cells and stomata had a direct effect on drought tolerance in the seedling stage of B.napus.At the same time,the stomatal opening of leaves was tested and it was found that drought-induced stomatal closure was more obvious in Bn5-001 than that in the other three B.napus varieties,indicating that Bn5-001 was easier to reduce leaf water loss to response to drought stress.Then we detected the expression of drought response gene in the four B.napus leaves.The expression of drought response gene was lower in drought-tolerant variety Bn5-001.The drought-induced expression patterns of some genes were negatively correlated with the drought tolerance of plants.These results indicated that the drought-tolerant variety Bn5-001 had strong water retention ability and thus weakened the expression of droughtresponse gene.To further reveal the relationship between drought resistance and leaf growth,we conducted dynamic analysis on leaf area and epidermal cell growth in Bn5-001.The results showed that drought stress significantly inhibited the division and growth of pavement cells and stomata.At the same time,the test of stomatal opening showed that stomatal development was significantly inhibited under drought stress.In order to explore the effect of plant hormones on leaf growth response to drought stress in rape seedlings,we detected the content of plant hormone under drought stress in Bn5-001 leaves.The results showed that abscisic acid(ABA)was obviously induced by drought,while gibberellin(GA)was inhibited in Bn5-001.Exogenous application of ABA inhibited leaf growth and decreased the number of cells and stomatal opening in normal conditions.However,exogenous application of GA could slightly promote the growth of leaves,and increase the number of cells and stomatal opening under drought conditions.Therefore,the inhibition of leaf growth under drought stress is partly caused by the increase of ABA and the decrease of GA in plant.Transcriptome analysis of Bn5-001 seedling leaves under drought stress showed that drought significantly affected the expression of 1,330 genes,of which 593 were up-regulated and 737 were down-regulated.GO analysis showed that the differentially expressed genes were mainly related to growth and development,biosynthetic metabolism and REDOX process.In conclusion,this study identified the drought-tolerant variety Bn5-001 among the four B.napus varieties by means of physiological,cytological and molecular biological experiments,and explained how the seedlings regulated their leaf growth,stomatal development and opening to improve drought tolerance under drought stress.It provides a theoretical reference for further study on the molecular mechanism of stomatal precursor cells responding to drought stress and inhibiting the occurrence of downstream epidermal cells. |
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