Physiological And Molecular Basis Of Drought Resistance Enhanced By Si Application In Sugarcane

Sugarcane is the most important sugar crop, and cane sugar occupies over90%of sugar production in China. However, sugarcane crop is planted in hilly unpland areas, where irrigation is not available, and drought has become one of the major limiting factors for sugarcane production in China. It is most effective to breed drought tolerant sugarcane varieties to improve the drought resistance of sugarcane in commercial sugarcane production. However, the efficiency of sugarcane breeding is low because of the complex genetic background of sugarcane, it is necessary to exploit other supplementary approaches to improve the drought resistance of sugarcane in practice. In the present study, seedcane setts were cultured in solution to investigate the physiological and molecular mechanisms of drought resistance improvement in sugarcane enhanced by Si application using real-time PCR,2-DE and MS with two sugarcane varieties, i.e. strong drought resistant variety ROC22and weak drought resistant variety ROC16. The main results were as follows.1Effects of Si application on physiological and biochemical parameters in sugarcane under PEG stressThe relative water content was dramatically decreased by PEG treatment but it could maintain higher in PEG+Si treatment. Both PEG and PEG+Si treatments could result in an increase in proline, H2O2and malondialdehyde (MDA) content but the plants applied with Si were found to reduce the accumulation of MDA. The overproduction of H2O2in plants treated with PEG stress was accompanied with higher activities of SOD, POD, CAT, GR and APX, but this increase was further promoted by Si treatment. The results suggest that though the tolerant variety showed an enhanced protective system against drought condition, application of Si further improved its tolerance by continuously triggering the over expression of antioxidative defense system.2Effects of Si application on chlorophyll fluorescence parameters and mineral nutrient absorption in sugarcane under PEG stressThe PEG stress was found to reduce the chlorophyll content, maximal PS II efficiency (Fv/Fm) and quantum efficiency of PS II (ΦPSⅡ) in sugarcane, while Si application decreased the degradation of chlorophyll, and counteracted, at least in part, the decrease in Fv/Fm and ΦPSⅡ.The silicon content in shoot and root was significantly increased by the Si treatment. The silicon content in the drought resistant variety ROC22is higher than the weak drought resistant variety ROC16. In addition, the PEG stress decrease the mineral nutrient level in sugarcane, and the Si application decreased the degradation of mineral nutrient content. The change of mineral nutrient level in ROC16is greater than that in ROC22under PEG stress. These results suggested that silicon application is useful to alleviate the PEG stress on sugarcane plants through enhancing the photochemical efficiency and adjusting the mineral nutrient absorption in sugarcane.3. Effects of Si application on protein expression in sugacane under PEG stressThe results of2-D gel electrophoresis analysis showed that32differential protein spots were detected under PEG stress and PEG stress plus Si application conditions in the two sugarcane varieties, and23of them were successfully identified through mass spectrometry. The23proteins were devided into six categories. Six proteins participate in photosynthesis, accounted for26.09%, including cytochrome b6-f complex iron-sulfur subunit, chlorophyll a-b binding protein, ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit,23kD polypeptide of photosystem II and chloroplast-localized Ptr ToxA-binding protein;6proteins participate in defense responses, accounted for26.09%, including thioredoxin M-type, quinone reductase, super-oxide dismutase, Cu/Zn superoxide dismutase glutathione S-transferase and temperature-induced lipocalin;3proteins participate in protein processing, accounted for13.04%, including BRII-KD interacting protein peptidyl-prolyl cis-trans isomerase and proteasome subunit alpha type6, putative;3proteins participate in stress resistance, accounted for13.04%, including heat shock protein17.2, nucleoside-diphosphate kinase-like protein, drought inducible22kD protein;2protein participate in cell growth an division, accounted for8.70%, including auxin-binding protein and keratin; and3proteins are unclassified, accounted for13.04%, which are hypothetical proteins. 4. Cloning and expression analysis of drought resisitance genesFour drought resistance genes were cloned by RT-PCR. A full length of SoNDPK1gene was obtained and the cDNA had686bp. A full length of SosHSP gene was obtained and the cDNA had659bp. A full length of SoDIP gene was obtained and the cDNA had402bp. A full length of SoCYT gene was obtained and the cDNA had796bp. The results of quantitative real-time PCR analysis showed that the mRNA of SoNDPK1was increased initially and then decreased with time of PEG stress. SoNDPK1gene increased significantly in the Si treatment. The mRNA of HSP was decreased initially and then increased with time under drought stress. SosHSP gene had the most abundant expression at96h after water stress treatment, while in the PEG+Si treatment, the highest increase appeared at144h. The mRNA of CYT was decreased with time under drought stress. The Si application decreased the degradation of SoCYT gene. SoDIP had the most abundant expression at30h after PEG+Si treatment, and expression of SoDIP in the PEG+Si treatment is higher than in the PEG treatment. It indicated that the expressions of the four genes were increased in different extent under Si treatment, which refleted that the role of these genes mediating signal transdution was enhanced, the capacity of antioxidant defense was increased, and the structure of membrane was relatively stable, thereby increased the drought resistance of sugarcane.