The Photorespiration Charactertistics Of The Transgenic Pepc Rice And Its Protective Role Under High Light Intensity And Salt Stress

With the environment being destructed, there are more and more researches for plant defense capacity.And now many studies have found that the presence of photorespiration in C3plants plays an important role in the resistance of the plant.If the photorespiratory path way is inhibited under stress, the plant will be more susceptible to destruction. Rice, as one of the major food crops in China, has aways been the focus of attention, especially on high yield and resistance of rice.Now researchers have built a C4photosynthetic pathway into the rice and tried to improve the production and resistance. PEPCase, as the key enzyme in C4pathway, has always been the focus of C3crops transferred into C4. Whether the rice that transfered with pepc of C4plants has a better performance of photosynthesis and stress tolerance? If the answer is positive, what is the role of photorespiration?In this study, Japanese rice Kitaake (WT) and the pepc transgenic rice (PC) were used.and the sixth leaves when they were fully expanded were used to measure the value of photorespiration.Treatments were as follows:(1) Control;(2)2000μmol m-2s-1PAR for2hours (3)160mM NaCl for8hours;(4)160mM NaCl/2000μmol m-2s-1PAR+inhibitors into the liquid nutrient medium for rice or the leaves of rice.The inhibitors are Isoniazid and NaHSO3which were smeared on the leaves for30min.Then the photosynthetic gas exchange parameters, the chlorophyll fluorescence parameters, the Chlorophyll content, the value of photorespiration, the PEPCase, RuBPCase, GO and RuBPOase activities, the content of Rubisco large subunit and the amount of photorespiratory metabolites of the sixth leaves of WT and PC were analyzed and compared, in order to clarify the protective effect of photorespiration.The result showed that:(1) under both stress, the photosynthetic gas exchange parameters, the net photosynthesis rate and the CO? carboxylation rate in the leaf of PC were higher than those of WT, the results show that the Pn of PC is18umol CO2m-2s-1and16μmol CO2m-2s-1, meanwhile the figure of WT is only15μmol CO2m-2s-1and13μmol CO2m-2s-1, respectively, but the the CO2compensatory points opposite, WT (80.6 μmol mol-1,89.3μmol mol-1), PC(76.4μmol mol-1,82.6μmol mol-1)and that showed WT was higher than the PC.So those illustrated that the stress tolerance of PC is better than WT. And After the treatment of inhibitors, the decrease of photorespiration of PC is higher than that of WT. It is surmised that the photorespiration of PC is stronger than WT.(2) whatever treatments, in total, the fluorescence parameter showed that the resistance of PC is better than WT.(3) The treated WT and PC, the activity of RuBPCase and the contents of Rubisco large subunit in the leaves of WT is worse than PC.This also proves that the resistance of the PC does better thanWT.(4) Under various treatment conditions, the results of the value of photorespiration, that the percentage of WT is4%-5%higher than that of PC, the activity of GO and RuBPOase show that the photorespiration percent of PC is more than that of WT.(5) By different treatments of the rice, the amount of the metabolic products in photorespiration is different, such as glycolic acid, serine, glycine.The higher of the percentage in photorespiration is, the more of the relative qualities in metabolites is, and the value of PC is higher than that of WT. The consequence demonstrates that after treatments by more photorespiration PC has a better resistance to the environment.