In addition, the gene(s) controlling stem solidness
was mapped based on an F2 population derived from a cross between a solid stemmed variety and a hollow stemmed one. The result will be helpful for molecular marker assisted selection (MAS) for solid stem in wheat breeding. Solid stemmed wheat line Xinongshixin (XNSX), hollow stemmed Line 3159, the F1 and F2 populations from cross XNSX/Line 3159 and Chinese Spring (CS) were planted at Changping Experimental Station, CAS, Beijing, China. Plant samples were collected from early April (three-leaf stage) Akt cancer to late June (mature stage). To evaluate stem solidness, more than 10 stems were randomly selected at post-anthesis and were cross-sectionally cut at the center of each internode. The level of pith solidness was rated
on a previously established score system [12] ranging from 1 to 5 (1 for hollow and 5 for solid). All samples were collected from main tillers. The internodes on samples were numbered consecutively from the base to the top of the stem. Sections were cut at the center of each internode and stained with either phloroglucine-HCl or Calcoflour (Sigma) according to the procedure described in our previous study [13]. The following morphological characteristics were measured and analyzed using a statistical software package attached to fluorescence microscope (Axioskop 40 with UV BIBW2992 molecular weight excitation, Protein kinase N1 ZEISS), i.e., outer and inner stem diameters, area of stem wall, radius of stem wall (RSW), width of stem wall (WOSW), area of vascular bundles (AOVB), area of transverse section (AOT), width of the mechanical tissue layer (WOMT), number of vascular bundles (NOVB), number of large and small vascular bundles (NLVB and NSVB), weight of the three lower internodes (WOL), and stem length. Carbohydrate contents (lignin and cellulose) were assayed according to the methods described previously [13], [14] and [15]. Three internodes from the bottom upwards
collected from stems were ground to fine powder in liquid nitrogen using a mortar and a pestle. Lignin content was assayed using the methods described by Kirk and Obst [16] and histochemical detection (the Wiesner reaction) following established protocols [17]. For cellulose staining, polyethylene glycol (PEG)-embedded sections (10 μm) were treated with a 0.005% aqueous solution of Calcoflour (fluorescent brightener 28, Sigma) for 2 min and then observed with a fluorescence microscope (Axioskop 40, ZEISS). Lodging resistance was ranked according to the measured resistance of stems to pushing, which was carried out on the bottom part of the stem following Kashiwagi and Ishimaru [18]. The data were analyzed by multiple ANOVA with 95% confidence limits using mean values measured for each genotype.