| Leaf photosynthesis in reconstituted tetraploid wheat
Nobuyoshi WATANABE Faculty of Agriculture, Gifu University, Gifu, Japan Three cultivars of bread wheat and their reconstituted teraploid (AABB) wheat were used as shown in Table 1. The discs were prepared from fully expanded leaf blades of two developmental stages of each strain. Seedling stages : for each strain, five seeds were sown in acrylic tubes filled with 0.7% agar, from which seedlings were grown at 25C in a growth chamber. The first leaves of seedlings fully expanded were used for the preparation of leaf discs. Flowering stages : these strains were grown in clay pots in a green house. When fully flowered, the discs of flag leaf were prepared. The reaction system for measuring photosynthesis with an oxygen electrode (Rank Brothers Inc., England) consisting of 3 ml of 50 mM HEPES buffer (pH 7.2) with 50 pieces of 3 mm diameter leaf discs at 25C. The photosynthetic reaction was started by adding 100 microl of 0.625 M NaHCO3 under illumination with a halogen lamp of 300 W. The chlorophyll content was measured according to ARNON (1949) using leaf discs taken from the same leaves after exygen evolution measurements. The photosynthetic rate was determined for six strains. Although the growth of reconstituted tetraploid wheat was not so vigorous as compared with genuine hexaploid wheat, the photosynthetic rate of reconstitutedd tetraploid wheat was higher than that of hexaploid wheat. The chlorophyll content was not significantly different between hexaploid and tetraploid wheats. In the first leaf, the tetraploid/hexaploid ratio of photosynthesis rate was 1.80 in Chinese Spring, 1.53 in Thatcher and 1.48 in Prelude. In the flag leaf, the ratio of photosynthesis rate was 1.02 in Chinese Spring, 1.19 in Thatcher and 1.69 in Prelude. These differences were found under a unit leaf area. The first leaf is less complex than the flag leaf. Its growth is influenced by grain reserves. The growth of the flag leaf is influenced by all previous leaves and grain filling. Nuclear ploidy levels in plant species are frequently correlated with changes in several cellular features, the number of cells found under a unit leaf area and the number of chloroplasts per cell. In wheat, the interpretation of the effect of cell size on photosynthesis is complicated by the effect of ploidy. When comparisons are made under a unit number of cells or chloroplasts, the ploidy effects are more informative because these were compared from a view point of function of cells and chloroplasts. |