| Rice is one of the main grain crops in China, so it's one of important task in rice breeding to keep improving its yield and quality. One important way to increase photosynthesis and yield of rice is to create rice with the C4 photosynthetic pathway. As the key enzyme in C4 pathway, PEPCase has always been the focus of C3 transfered to C4. Whether has the rice that transfered with pepc of C4 plants a better performance of photosynthesis and stress tolerance? If positive, what signaling molecules are involved?In this study, Japanese rice Kitaake (WT) and the pepc transgenic rice (PC) were used, and when the sixth leaves were fully expanded, they were treated with salt stress.Treatments were as follows:(1) Control; (2) 120 mM NaCl; (3) 0.4% n-Butanol and (4) 120 mM NaCl+0.4% n-Butanol to the liquid nutrient medium for rice.After four days treatment, the photosynthetic gas exchange parameters, the chlorophyll fluorescence parameters, the RuBPCase and PEPCase activities, the content of soluble proteins, the content of Rubisco large subunit and the level of carbonylated proteins, accumulation of hydrogen peroxide and superoxide anion of the sixth leaves of WT and PC were measured and compared, in order to clarify the effect of PA on pepc transgenic rice during the process of tolerating salt stress.The results showed that:(1) for the 120 mM NaCl treatment, the photosynthetic gas exchange parameters, the net photosynthesis rate and the CO2 carboxylation rate in the leaf of PC were higher than those of WT, but the CO2 compensatory point of PC were lower than that of WT, which indicated that PC was more tolerant to salt stress than WT. The decreasement in the net photosynthesis rate and the carboxylation rate of PC (or WT) under the 120 mM NaCl+0.4% n-Butanol treatment were more than the sum of that of PC (or WT) under the 120 mM NaCl treatment and the 0.4% n-Butanol treatment respectively, which indicated that PA could protect rice during the process of tolerating salt stress; (2) whatever the treatment, the constituents of chlorophyll fluorescence quenching of WT and PC varied with different respectively-namely qI, qE and qT, which indicated that the main mechanism of non-photochemical quenching are different in two rice cultivars. The fluorescence parameter Fv/Fm declined significantly when WT and PC were treated with 120 mM NaCl+0.4% n-Butanol, which also indicated that PA could protect rice to a certain degree during the process of tolerating salt stress. (3) Under various treatment conditions, the contents of Rubisco large subunit in the leaves of WT declined, whereas in the leaves of PC declined slightly only in the 120 mM NaCl+0.4% n-Butanol. This was similar to the result of RuBPCase activity:the RuBPCase activity in the leaves of WT declined significantly both in the salt stress treatment and the 120 mM NaCl+0.4% n-Butanol, but that of PC remained unchanged during the two treatments. The PEPCase activity in the leaves of PC was higher than that of WT. Due to the higher PEPCase activity in the leaves of PC in each of the treatments above, the pepc transgenic rice revealed a better ability in tolerating salt stress. (4) the accumulation amount of carbonyl Rubisco large subunit, H2O2 and O2ยท- in leaves were also measured in this study. The result showed that in the salt stress treatment, the content of carbonyl Rubisco large subunit, H2O2 and O2 in the leaves of WT were higher than those of PC, which indicated that PC Accumulated less reactive oxygen than WT in leaves,and suffered less oxidative damage. |
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