Physiological And Molecular Mechanisms Of Drought Resistance Of Different Sugarcane Varieties

Sugarcane is an important sugar crop.Sugarcane production in China mainly locates in poor upland field,and drought stress has become an important factor limiting the sugarcane production,so influencing producing of sugarcane greatly and limiting the continuing suitability development sugar industry.Making a deep study on physiological and molecular mechanisms of drought resistance is important to breed new drought resistant sugarcane varieties and develop drought resistant fanning technologies.In the present study,pot culture was used to grow two sugarcane varieties,drought resistant F 172 and drought sensitive YL 6,different drought stress and re-watering treatments were applied at seedling and elongating stages,respectively.The relationships between the drought resistance and various physiological indexes in different sugarcane varieties were investigated,the differential protein expressions in different sugarcane varieties under drought stress were compared with proteomics method,and cloning and expression analysis of four drought resistance related genes were done with RT-PCR and qRT-PCR.The main results are as follows.1.It was found that the activity of oxygen radical scavenging enzyme system including the contents of insoluble protein(ISP),peroxidase,superoxide dismutase(SOD),the activity of antioxidant protective enzyme catalase(CAT)and soluble su-gar(SS)in leaves of the drought resistant variety F 172 were significantly improved under drought stress,and the contents of malondialdehyde(MDA)and insoluble sugar(ISS)were relatively stable compared with the drought sensitive variety YL 6.The oxygen radical scavenging enzyme system in the drought sensitive variety YL 6 was lagged in response to drought stress with significant increases in MAD and ISS and decreases in SP and ISP in leaves.The physiological and biochemical differences indicated sugarcane varieties with different drought resistance had differences in resisting to drought stress at different growth stages.2.The differential protein expressions in leaves of seedlings of F 172 and YL 6 under severe drought stress were analyzed with two-dimensional electrophoresis.The analyses of 2-DE profiles with PDQuest software showed 28 and 20 differential protein expression spots in F 172 and YL 6,respectively,some expressions were up-regulated,some were down-regulated,some were new protein spots,and they were varied depending on the different resistance of sugarcane varieties.It is speculated that there are significant variations in protein richness in sugarcane varieties with different drought resistance.3.The 48 differentially expressed protein spots were identified with MALDI-TOF-TOF/MS,and biological information analyses were done.The results showed that 18 and 14 protein spots were identified from YL 6 and F 172,respectively,and they were divided in 8 categories based on the protein functions.The protein spots in YL 6 include 2 participating in oxygen radical scavenging,1 participating in cell growth and division,6 participating in photosynthesis,6 participating in basic metabolisms including energy metabolism,carbon metabolism,nitrogen metabolism,secondary metabolism,sugar metabolism,RNA processing,etc.,2 participating in protective response,and 1 is still unknown in function.The protein spots in F172 include 1 participating in oxygen radical scavenging,2 participating in photosynthesis,2 participating in cell growth and division,4 participating in basic metabolisms including sugar metabolism,energy metabolism,nitrogen metabolism,carbon metabolism,secondary metabolism,RNA processing,etc.,2 participating in information transfer,1 participating in protein processing,and 1 is still unknown in function.It is obvious that there are great differences in differentially expressed protein spots in sugarcane varieties with different drought resistance under severe drought stress,and the response mechanism is a comprehensive process related with multiple systems and levels.4.RACE and RT-PCR technologies were used gene cloning,and the full length sequences of 4 genes,glutamine synthetase gene(SoGS1),triose phosphate isomerase gene(SoTPI),a subunit of 20 s proteasome gene(SoPAA)and fructose 1,6-diphosphate aldolase gene(SoFBA)were obtained.The gene expressions were examined with qRT-PCR under the conditions of light drought,medium drought,severe drought,and 1 day after re-watering and 3days after re-watering.The SoGSl gene expressed varied in sugarcane varieties with different drought resistance,its relative expression increased continuously with drought stress duration in the drought resistant sugarcane variety F 172,and kept high level after re-watering.In the drought sensitive sugarcane variety YL 6,however,the SoGSl gene showed increase first and decrease later in its relative expression during drought stress,and reaching a peak in 3 days after re-watering.Similar trend was found in the relative expression changes of SoTPI gene for both F 172 and YL 6,but the expression in F 172 recovered fast and showed a peak in 1 day after re-watering while the peak in YL6 appeared in 3 days after re-watering.The SoPAA gene showed a trend of slow increase in F 172 during drought stress,and reaching its maximum in 1 day after re-watering,that is,as high as 20 time of the control.The relative SoPAA gene expression in YL 6 showed a slow decreasing trend during drought stress,and increased after re-watering and reached maximum in 3 days after re-watering.The relative SoFBA gene expression showed increase sharply after re-watering,indicating that the SoFBA gene plays an important role in response to water stress and re-watering.All the 4 genes responded to water stress in certain degree,and they have different functions,and participate in different protective pathways during water stress.