Has breeding altered the light environment, photosynthetic apparatus, and photosynthetic capacity of wheat leaves?

Whether photosynthesis has improved with increasing yield in major crops remains controversial. Research in this area has often neglected to account for differences in light intensity experienced by cultivars released in different years. Light intensity is expected to be positively associated with photosynthetic capacity and the resistance of the photosynthetic apparatus to high light but negatively associated with light-utilization efficiency under low light. Here, we analyzed the light environment, photosynthetic activity, and protein components of leaves of 26 winter wheat cultivars released during the past 60 years in China. Over time, light levels on flag leaves significantly decreased due to architectural changes, but photosynthetic rates under high or low light and the resistance of the photosynthetic apparatus to high light remained steady, contrary to expectations. We propose that the difference between the actual and expected trends is due to breeding. Specifically, breeding has optimized photosynthetic performance under high light rather than low light. Moreover, breeding selectivity altered the stoichiometry of several proteins related to dynamic photosynthesis, canopy light distribution, and photoprotection. These results indicate that breeding has significantly altered the photosynthetic mechanism in wheat and its response to the light environment. These changes likely have helped increase wheat yields.

[The value of studying liver function reserve in hepatic carcinoma by 13C-methacetin breath test].

OBJECTIVE: To investigate the characteristic of 13C-methacetin breath test (13C-MBT) as a tool to monitor the hepatic function of patients with hepatic carcinoma by comparing with Child-Pugh classification and general liver function. METHODS: Thirty-nine patients with primary liver cancer, 16 patients with hepatic metastasis and 14 healthy volunteers serving as controls were included in this study. According to Child-Pugh classification, the primary liver cancer patients were divided into A, B and C subgroups. All subjects received 13C-MBT and routine liver function tests after an overnight fast. The three major parameters of 13C-MBT i.e. maximum excretion rate before 40 min (Mvmax40), 13CO2 cumulative excretion of 40 min (CUM40) and that of 120 min (CUM120) were recorded and the two metabolism curves (DOB curve, MV curve) were made. RESULTS: (1) In the control, hepatic metastasis and primary liver cancer groups, both the DOB curve and MV curve were similar in shape; the peak time occurred at about 20 min after administration and then the curves lowered progressively. There were significant differences between the primary liver cancer group and the other two groups, but it was not statistically different between the hepatic metastasis group and the controls. The shape was obviously distinct in the groups A, B and C of primary liver cancer. The group A had a single sharp peak curve, group B a relatively flat peak curve with a lower level for a long time after the ascending phase and group C no clear excretion peak or even a negative curve. (2) As to the three parameters of 13C-MBT, there were statistical difference between the primary liver cancer group and the other two groups (P<0.05). Between hepatic metastasis group and controls, there was statistical difference about CUM120 (P<0.05), but no statistical difference about Mvmax40 and CUM40. While in the three groups with primary liver cancer groups, there was statistical difference between group A and B in Mvmax40 and CUM40 (P<0.05), but no statistical difference between group B and C. As to CUM120, there was statistical difference only between group A and C. (3) Comparing the three parameters of 13C-MBT with routine liver function tests, there was negative correlation with TBA, positive correlation with Alb, PA, ChE and no correlation with ALT, AST, TBil, gamma-GT, ALP and PT. (4) There was a good consistency between 13C-MBT and Child-Pugh classification in the evaluation of liver function of patients with liver cancer (Kappa=0.647, P<0.05). CONCLUSION: The value of the three parameters of 13C-MBT is decreased with severity of the liver disease and 13C-MBT may be used to evaluate the reserved hepatic function in patients with primary liver cancer with a diagnostic value equivalent to Child-Pugh classification. The study further confirms that 13C-MBT has correlation with TBA, Alb, PA and ChE.