| Significant differences in net photosynthetic rate (PN) of flag leaves between Near-Isogenic Lines (NILs)wheat (154 and 212,23 and 94) grown in the field were observed, in order to identify the reasons for the difference, the physiological basis of flag leaves in different levels were studied, which included ultrastructure of stomata , chloroplasts, cytological features of mesophyll cells and activity of enzyme involved carbon metabolism in flag leaves during the ontogenesis of wheat. The main results are as follows:The results revealed that there were no appreciable differences in stomatal size and density, and the number of chloroplasts per cells were similar, also with a typical membrane system of stroma and grana thylakoids, but it was found that mesophyll cells of 154 and 23 contained more protuberances and the percentage of mesophyll cells possessing more than five protuberances was higher in 212 than that in 94, no significant difference of grana thylakoid membrane was observed between NILs.Net photosynthetic rate (Pn) in flag leaves of NILs increased from booting stage to flowering and reached their maximal Pn about 16 days after anthesis, and after that, declined gradually. There was no significant difference of Fv/Fm between two NILs. A similar trend is observed forФPSII and rate of photosynthesis. 94 had continued for a relatively long period of Pn.Chlorophyll content in flag leaves during anthesis and grain filling stages had the same trends as Pn and reached their maximal Pn about 10 days, and after that, declined gradually. There were no appreciable differences among 154 and 212, but the chlorophyll content in 94 was higher than 23. Soluble protein content in flag leaves increased after anthesis, and reached its maxima at about 6 days after anthesis, thereafter, decreased. There were no appreciable differences among NILs. Enzymes activity assay demonstrated that the activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), stromal fructose- 1,6-bisphosphatase (sFBPase) were much higher in 154 than in 212, and the activity of Ribulose-1,5-bisphosphate Carboxylase (Rubisco) were slightly higher in 154 than in 212, the activity of Aldolase were similar in these two NILs, the activity of Rubisco was higher before 21 DAA in 23 than 94, after that, lower than in 94 , sFBPase were much higher in 23 than in 94 after 21 DAA, GAPDH activity was much higher in 23 than in 94 during the whole stage. The cytosolic fructose- 1, 6-bisphosphatase (cFBPase) activity was higher in154 than in 212 before 16 DAA, after that, the difference was not obvious. SPS has the same trends with sFBPase. The activity of cFBPase after 21 DAA was much higher in 23 than in 94, and the SPS activity was much higher in 23 than in 94 during the whole stage. Hence the differences in PN between the two NILs result from the high percentage of mesophyll cells possessing more protuberances and higher activity of some enzymes involved carbon metabolism.Changes of activities of antioxidative enzymes such as ascorbate peroxidase (APX) and peroxidase (POD) in flag leaves had the same trend with Pn. While the activity of CAT decreased from anthesis. No obvious difference was observed in NILs with CAT activity, but the APX activity was much in 154 than in 212, the same result was observed in 23. The POD activity was much higher in 154 than in 212, but was lower in 23 than in 94.The flag leaf area of 154 and 212 had no obvious difference, and the yield was 8% higher than 212. The flag leaf area of 94 was 14% greater than 23, and the yield was 4% higher than 23, Although the Pn of 154 and 23 was higher than 212 an 94, the relationship among leaf area and Pn was not clear, the yield of wheat was not only decided about the Pn, but also about the flag leaf area. |
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