Effects Of PEPC On Rice Drought Resistance

Recently, the need for food is increasing more and more as the continue growing population of world. So it demand the agronomist to find some ways to increase food production. Many scientists believe that the improvement in photosynthesis will be an important way to increase crop yield after the "Green Revolution" and using of heterosis. Scientists from IRRI suggest that creating the C4 rice to increase the photosynthetic rate(Pn) is one way to meet food demand in Asian. In recent years, several studies have reported that using C4 transgenic technology to improve the photosynthesis in C3 plant could increse the Pn and crop yield. However, crop production could not reach to higher yield with high Pn only. Because they would inevitably suffer from abiotic stress in field, and the photosynthesis is sensitive and vulnerable to stress inhibition, especially drought stress. Today, with global climate changing, drought stress became one of the main natural disasters in crop production process. Therefore, study on drought tolerance in crop has been becoming an important research field.PEPC plays an important role in resisting stress in plants. Drought, salt, cold and other stresses could induce the expression of PEPC involved in plant response to environmental stress. However, the regulation mechanism of PEPC in rice under stress is still not clear. In the present research, a large number of PEPC transgenic rice lines were used to study the drought tolerance in upland field. First, the photosynthesis and drought tolerance of transgenic rice and control were compared under different water conditions. Then, to analyse the function of foreign PEPC in rice. Finally, to clarify the regulation mechanism of PEPC on photosynthesis and drought tolerance in rice. Results showed as follows:1. Maize PEPC gene had already expressed in rice, and it was induced by drought stress. In upland field(soil moisture was about 18%), the activity of most PEPC transgenic lines were higher than control, the highest one increased by 50 fold, only a few transgenic lines were lower than control. More than 50% of PEPC transgenic lines have a 10-30 fold PEPC activity that of control. Therefore, we suggest that PEPC gene may play an important role in the regulation on drought tolerance in rice .2. PEPC transgenic rices maintain higher Pn than control under drought stress. In upland field, Pn of both transgenic rices and control all declined, but more so in control. Pn of 95% and 98% (Flowering stage and Filling stage) transgenic rice lines were higher than control, 73% and 65% were significant. It demonstrated that the higher Pn of transgenic rice were depend on that PEPC reduced the drought inhibition on photosynthesis in rice. Correlation analysis showed that there was no significant correlation between PEPC activity and Pn. It seemed that PEPC could improve photosynthesis only when the expression at a certain level, too high or too low activity of PEPC would bring little impact on the photosynthesis in rice. This may because of the limit accumulation of malate in intracellular which was produced by PEPC catalysis.3. PEPC transgenic rice exhibited higher capacity of photoinhibition tolerance under drought stress. In the present research, the Fv/Fm, qP and chlorophyll content decreased less, and NPQ, zeaxanthin(Z) content increased more in transgenic rice under drought stress. It indicated that PEPC transgenic rice can either convert excess light energy into chemical energy to maintain higher photochemical efficiency; or dissipate excess light energy to protect the photosynthetic apparatus. So the photosynthsis response to drought stress was enhanced.4. PEPC transgenic rice exhibited higher capacity of drought tolerance, which mainly rely on the anti-oxidate and osmotic regulation ability under drought stress. With increased drought stress, O2-. production rate and MDA content decreased less than control. It mainly depend on the higher activity of antioxidant enzymes (SOD and CAT) in transgenic rice which can detoxicate O2-. and MDA effectively. In addition, transgenic rice under drought stress had high content of malate, proline and solube protein which play the role of maintaining cell turgor.3. Growth status and crop yield of PEPC transgenic rice were significant better than control in upland field. Transgenic rice had a higher specific leaf area(SLA) in upland field. It indicated that transgenic rice had higher capacity of material accumulation and transformation. Thus, in upland yield, transgenic rice had a higher yield which mainly depend on the increased grain number.