Drought Tolerance Evaluation Of Indica Rice Near-Isogenic Lines And Roles Of Nitric Oxide In Rice Under Drought Stress

Evaluating and identifying drought tolerance related phenotypes and physiological charactersusing rice near isogenic lines will provide useful information to screen and breed drought tolerance ricevarieties. According to the effects of drought stress at flowering stage on fertility of28indicanear isogenic rice lines, changes of phenotype, water and photosynthesis characters were studied in riceflag leaf. Furthermore, the relationships among phenotype, water and photosynthesis characters andfertility of rice were analyzed to indentify the best indicators related with rice drought tolerance. Theresults showed that indica near isogenic rice lines had different phenotypes and there was no obviouscorrelation between drought tolerance and phenotype under drought stress. However, the correlationcoefficient between drought tolerance indexes and changes of water content, water potential, stomatalconductance of flag leaf were0.614**,0.514**and0.541**, respectively. This indicates that ricedrought tolerance has a correlation with water content, water potential and stomatal conductance. Inaddition, except the correlation coefficient between drought resistance indexes and changes of Fv/Fm offlag leaf (0.470*), there was no obvious correlation between rice drought tolerance and photosyntheticphysiology and agronomic phenotype characters. In summery, the changes of water physiologyparameters could be used as indicators for screening rice with high drought tolerance, and theircontribution to drought tolerance rank as follows: water index> photosynthetic indicator>morphological index.Nitric oxide (NO) plays a role in response to a series of abiotic stresses as gas signaling molecularin plants. It is useful to study the changes and functions of NO in rice under drought stress to discovernew mechanisms related with rice drought tolerance. In this investigation, the results showed thatdrought stress induced a significant increase of NO in rice leaves by increasing nitric oxide synthaseactivities. Using sodium nitroprusside as NO donor and cPTIO as NO scavenger, we demonstrated thatNO decreased drought induced increment of hydrogen peroxide, malondialdehyde, ion penetration andleaf water potential and improved rice drought tolerance. In addition, foliar sprayed of cPTIO, a nitricoxide scavenger, increased the toxicity of drought stress. NO had no obvious effect on osmoticregulation substances such as soluble sugar, soluble protein and proline content or antioxidant substancesuch as ascorbic acid and glutathione content. Further studies indicated that NO increased ricetolerances by decreasing transpiration rate. In addition, NO also alleviates drought induced oxidativestress by regulating superoxide dismutase and catalase activities. In summary, NO play significantsignaling roles in response to drought stress in rice.