The second experiment was carried out to examine the mesophyll conductance responding to ABA application (Mizokami et al., 2017). This experiment was done in a similar setting to the first experiment with the investigation of the change in the CO2 levels. Mizokami et al. grew each plant, Col-0, ost1, and slac1-2 in a pot that were placed in a chamber that provided a photoperiod of eight hours, 23 degrees Celsius for day temperature, 21 degrees Celsius for night temperature, humidity of 60%, ambient CO2 of 390μmol and a Hoagland solution twice a week (Mizokami et al., 2017). In this ABA application experiment, the CO2 level in the chamber was not manipulated and stayed constant for two weeks. Mizokami et al. first made a tiny slit with a razor in the Arabidopsis thaliana’s petiole to make a space to inject the ABA solution so that the plants will not wilt (2017). They kept these plants in the dark for about 15 minutes before turning on the fluorescent lamp again to prevent the slit from embolism. After the plant is adjusted to the slit, an artificial xylem sap called AXS was injected and the fluorescent lamp in the chamber was turned on shining a 600μmol light on the plants. Then the initial photosynthetic rate was measured (Mizokami et al., 2017). When the initial photosynthetic rate and the atmospheric conditions were recorded, Mizokami et al. applied 100μl of ABA solution gradually into the same slit where they injected the AXS solution (2017). It took an hour and a half to complete this injection, and they measured the photosynthetic gas exchange parameter to compare the results from the initial data. Not only the measurements, but also ABA contents in the leaf was observed (Mizokami et al., 2017). By using liquid nitrogen to freeze the leaf and removing the veins from it, the contents were determined by using a liquid chromatograph and a mass spectrometer. Finally, to evaluate the mesophyll conductance, Mizokami et al. created an equation (Figure 1) to analyze how sensitive the mesophyll is to both ABA and CO2 levels (2017).
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