| Reactive oxygen species (ROS) have been rewarded wide notice of scientists from many fields because of its' close relation with death, diseases, stresses, damages and their resistance. Studies found ROS , since its' reactive characteristic, do serious harm to gene protein, membrane, and so do harm to cells. On the other hand, it can work as the second messenger and induce the production of its' resistant system.Rice is a major resource of food so that improvement of the production of rice is of significant importance. But senescence and stresses such as cold and radioaction make it difficulty. Aand reactive oxygen species play a role when these bad enviroments work. It was supposed that ROS might work as a kind of second messenger. So it is not only bringing harm to the organic body, it may also induce the expression of some kind of resistant system.Plants have developed a ubiquitous resistant system including enzymes and so me biological molecules including SOD, CAT POD APX,GR and VE, GSH Asc and so on. In plants' normal life, the resistant system can clear endogen ROS and keep their lives going on smoothly. But when plants are in stresses, there will be found a oxidative burst.We study on the resistant system respectively when the rice seedlings are in senescence. As the photosynthetic cells are likely to be in the oxidative stress during senescence, we simultaneously studies the characteristics of fluorescence of chlorophyll a. The photosynthetic rate of leaves of rice cultival SY63 decreases partly because of the decrease of pigment and the change of the function of PS II and the activity of the resistant enzymes increase firstly and then decrease.While in XZX the photosynthetic rate decreases most likely because of the decrease of the efficiency of the noncycle electron transport, and the activities of enzymes in the Asc-GSH cycle keep increasing.When rice seedlings was treated with H2O2, we found it firstly damage xylem. And when the leaves are severed and then treated with H2O2 of different concentrations and different time, the low concentration didn't damage the leaves. It may be that the resistant system is able to clear the ROS. When the concentration is high, the production of MDA in the leaves increases. And the activity of the resistant system increases apparently firstly and then after treated for 16 hours it decreases to a low level. It may be caused by the harm of H2O2.When rice seedlings are treated with NaCl, the leaking percentage of electric conductivity and Na+/K+ increases. And the expression of the resistant system are improved. And GSH can be absorbed and used by rice so that it can improve its' resistant ability. |
