| In this study, we used two wheat near isogenic lines(NILs)(line 154 and line 212) with significant difference in photosynthetic rate as materials. The NILs of wheat were selected from crossing winter wheat Xiaoyan 54×8602 using the net photosynthetic rate(Pn) as a physiological selection index from the progeny, with line 154 as the high photosynthetic rate line. The photosynthetic oxygen evolution rate, Hill reaction activity of seedlings and photosynthetic parameter, Pn-Ci curve, antioxidant enzyme activities, antioxidants contents, observations of the ultrastructure of chloroplast, chlorophyll content, source-sink metabolism related enzyme activities and substance content of flag leaves were measured in order to explore the differences of the two NILs in photosynthesis. Main results are as follows:(1) At the seedlings stage, the high photosynthetic rate line 154 had higher photosynthetic oxygen evolution rate and hill reaction activity.(2) The net photosynthetic rate(Pn) of the two wheat NILs rose after anthesis and peaked on the 10 th day after anthesis. The Pn of line 154 was significantly higher than that of line 212 during the whole stage. While Pn and Ls declined, Ci of both lines raised, which indicate that the decline of Pn of the two wheat NILs was caused by non-stomatal limitation.(3) The maximal carboxylation efficiency(Vcmax), as calculated from the Pn-Ci curve, was higher in line 154 than in line 212. This indicated that significant differences of Vcmax may be one of the reasons for the difference in Pn of the two wheat NILs.(4) During the whole grain-filling stage, the activity of SOD in flag leaves in both NILs increased after anthesis and thereafter declined along with the leaf aging process. The SOD activity of line 154 was always higher. The CAT activity of line 154 was always higher than line 212, and reached significant differences on the 9th and 11 th days after anthesis. The APX and POD activities changed in a similar trend as SOD activity and peaked on the 11 th day after anthesis. Line 154 always had higher APX and POD activities during the whole stage.(5) During the whole grain-filling stage, the As A content changed in a declining trend. The As A content of line 154 was always higher than line 212. The contents of DHA and total ascorbate almost remained unchanged. The ratio of As A/DHA was always higher in line 154 and reached significant differences on the 15 th days after anthesis. The content of GSH of both lines declined after its peak, and line 154 showed more GSH content than line 212. The contents of GSSG and total glutathione showed a trend of increase. The ratio of GSH/GSSG was higher in line 154 than line 212.(6) There were significant differences in the number of grana per chloroplast and lamella per granum between the two wheat NILs, but there were no significant differences as for the number of chloroplasts per cell. The data suggest that the 154 line contained more grana and that its thylakoids were stacked more thickly than line 212. Therefore, the 154 line had a much stronger photosynthetic capacity.(7) The results of some sucrose-starch metabolism related enzyme activities and substance content revealed that line 154 had higher leaf sucrose phosphate synthase(SPS) activity, grain sucrose synthase(SS) activity and grain ADPG pyrophosphorylase(AGPase) activity. This ensured that the photosynthate of line 154 could be transported from leaves to grains and translated into starch in a timely and effective manner, thus relieving any end-product inhibition on leaf photosynthesis, which also contributed to the maintenance of its high photosynthetic rate. |
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