| Rapeseed(Brassica napus L.)is one of the most valuable oil crops due to its high nutritious value and ample supply of oil contents.It plays an important part in the human food,and livestock feed industry as well as the source of raw material in the industrial world.Rapeseed production has a large share(about 50%)regarding edible oil,in China.On the other side,climatic adversities such as drought stress impart negative effects through oxidative damage on rapeseed growth and development,ultimately yield.Moreover,seed germination and seedling stages are adversely affected by drought stress.The present study is conducted to reveal the drought stress effect on rapeseed during seed germination and seedling development.Besides,our investigation provides the evaluation of cultivars that can be further utilized in the research field,also the screening approach provides an assessment of tolerant and sensitive cultivars,that knowledge can be used for further rapeseed improvement programs.Moreover,our study provides knowledge about the responsive mechanisms of tolerant and sensitive cultivars.The main results are summarized below.1.In this investigation,we elucidated the effects of drought stress on rapeseed germination and seedlings by simulating drought conditions using PEG-6000,whereas 24 cultivars are evaluated based on seed germination and seedling growth traits.Afterward,tolerant cultivars V5(JYZ 158)and V24(FY520)and sensitive cultivars V19(YG2009)and V12(NZ1838)were screened out for further research.Results illustrated that drought stress negatively influenced all studied cultivars;however,the degree of influence was varied for each cultivar suggesting the potential of their tolerance against drought stress.We employed a screening approach to select the tolerant and sensitive cultivars.The studied morpho-physiological mechanisms in drought-tolerant and sensitive cultivars revealed that the enzymatic and osmoregulatory mechanisms are highly efficient in the tolerant cultivars as compared to sensitive cultivars.The influence of drought stress on physiology,metabolic mechanisms,and development is explored in drought tolerant and sensitive rapeseed cultivars which suggest that the drought tolerance is coincide with various classes of metabolites and physiological mechanisms.Moreover,the accumulation of osmolytes and activity of the antioxidant enzyme increased under drought stress in both tolerant and sensitive cultivars,however,it was higher in tolerant as compared to sensitive cultivars,such as proline level increase by 1161.3%,1282.9%,1072.54% and 922.9%,and enzyme activity i.e.,CAT enhanced by 108.8%,107.9%,92.92% and 97.51% in V5(JYZ158),V24(FY520),V19(YG2009)and V12(NZ1838),respectively,under drought stress.Therefore,the seed germination(FG%;non significantly reduced in tolerant cultivars,while 53.50% and 38.20% in V19(YG2009)and V12(NZ1838),respectively)and seedling growth indicators of tolerant cultivars showed relatively lower reduction as compared to sensitive cultivars.Moreover,the reduction in seed germination,shoot and root fresh weight,dry weight,root length and shoot length,is higher in sensitive as compared to tolerant cultivars.Further,this study provides a sound basis for assessment of drought tolerance among sensitive and tolerant cultivars,also outlined the significance of osmotic and enzymatic regulators for successful germination,seedling growth and to better predict the adaptability of Brassica napus L.under drought stress.2.Seed germination is one of the complicated traits in the plant life cycle,which is accomplished by the interaction of various complex processes,seed reserve mobilization,and utilization,also environmental factors.The response is varied according to genotype,the environment,and the interaction between these factors.We have carried out a physiochemical approach to get insight into the reserve mobilization process of rapeseed seed during germination,within two genotypes(high oil and low oil content cultivars)having the contrasting ability of germination under normal condition as well as drought stress.In the present study,fatty acid composition,soluble sugar,and protein are assessed.Furthermore,we have observed that earlier metabolism of reserves seems to generate differences in germination rate between cultivars of rapeseed,which in turn might be due to the difference in oil contents.The comparative effects of drought stress on seed performance,growth parameters,free proline content,and lipid peroxidation,were studied in both rapeseed cultivars.Results showed that cultivar with high oil contents showed higher germination(two times in high oil content cultivar at start point 18 h of germination under normal condition while germination start earlier in high oil content as compared to low oil content cultivar under drought stress),water contents,and reserve mobilization.Moreover,in high oil content cultivars,the number of oil bodies is higher(269.2%,and 114.0% under normal while 187.0% and 99.11%,at 12 h in high oil content and low oil content cultivar,respectively),which might provide energy for germination,also the protein and sugar active metabolism(TSS;enhancement of 28.43% in high oil content and 6.51% in low oil content cultivar during 6-12 h)is higher in high oil content,as compared to low oil content cultivar under normal condition as well as drought condition.The degree of unsaturation was higher in high oil content cultivar as compared to low oil content cultivar(C18:3;increased by 19.31% and 1.74% at 12 h in high oil content and low oil content cultivar,respectively),which suggests the greater protection against drought stress damages. |
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