Response of Thai rice varieties under elevated CO2 concentrations

Samples of leaves, stem and roots will be used in determining anatomical changes related with the effect of elevated CO2 concentration. The leaf blade thickness will be determined from the blades of the fully expanded leaf at tillering stage and from the flag leaf at reproductive stage. Leaf sections will be obtained by from the middle of the leaf which will be used to determine the blade thickness. Segments will be embedded in 5% (w/v) agar and will be sliced to produce cross sections with 100 µm thickness using Leica Fully Automatic Vibrating blade microtome (VT 1000S) (Leica Biosystems Division of Leica Microsystems Inc., Buffalo Grove, IL, USA). Cross-sections will be observed under a light microscope (Leica compound microscopes) at 4 × magnification equipped with digital camera. Thicknesses at all ridges of small VBs will be determined and will be reported as the average. The length and width of each blade will be measured by counting the number of the small vascular bundles and the epidermal cell files. The thickness of the leaf per mesophyll (Tleaf/Tmes, um), the cross-sectional area of mesophyll cells (Acell, um), the ratio of mesophyll cell (Ames), bullifom cell (Abf), main vein (Amain vein), major vein (Amaj vein), and minor vein (Amin vein) area to cross-sectional area (Across), and the lengths between to neighboring major/minor vascular bundle (Lmaj vein/Lmin vein, um) will be determined. Mesophyll cell number per cross-sectional area (NO mes cell/Across, number um-2) was calculated as a quotient of dividing Ames by Acell. Leaf, stem and root xylem will be evaluated by preparing cross-sections and the and the total number of vascular bundles (N) will be measured and counted from the photographs. Root number and length of both nodal and lateral roots will be counted and measured for length and diameter.