Tomoshiro Takeda

An investigation for the occurrence of C4 photosynthesis in the Cyperaceae from Australia

Two hundred and twenty species of 38 genera in the Cyperaceae from Australia were examined for the possible occurrence of the C4 photosynthesis and the anatomical features of leaves and culms. The Kranz type of anatomy and the carbon isotope ratios typical of C4 plants were found in 84 species in the following six genera of four tribes belonging to subfamily Cyperoideae:Bulbostylis, Crosslandia, andFimbristylis (Fimbristylideae);Lipocarpha (Lipocarpheae);Cyperus (Cypereae);Rhynchospora (Rhynchosporeae). The anatomical observation revealed that the C4 species possessed any one of the three Kranz anatomical types found by previous investigators. It was suggested that in the Cyperaceae the C4 syndrome evolved independently within several taxa of the subfamily.The relative distribution of C3 and C4 species of the Cyperaceae in Australia was investigated by use of floristic data. It was recognized that the C4 species dominated in the northern part of the continent which was characterized by tropical and subtropical savannas and hot dry areas with summer rainfall, and the C3 species in the southern part, which contained temperate areas and mediterranean climatic areas with winter rainfall.

The occurrence of C4 species in the genusRhynchospora and its significance in kranz anatomy of the cyperaceae

Rhynchospora rubra was found to have a low CO2 compensation point, high δ13C value, Kranz leaf anatomy, starch present in the bundle sheath cells and narrow interveinal distance. These observations suggest thatR. rubra is a C4 plant. A further anatomical survey revealed seven otherRhynchospora species presumably having the C4 photosynthetic pathway. In the family Cypraceae C4 plants therefore occur in the tribe Rhynchosporeae as well as in the Scirpeae and Cypereae. The C4 species ofRhynchospora have a normal Kranz type of leaf anatomy, although the C4 species ofCyperus andFimbristylis presently known have an abnormal one in which the mestome sheath without chloroplasts is interposed between the Kranz tissue and the rest of the chlorenchyma. Thus inRhynchospora the Kranz tissue is in direct contact with the rest of the chlorenchyma, and it is suggested that the Kranz tissue may be homologous with the mestome sheath.

Leaf ultrastructure of C4 species possessing different Kranz anatomical types in the Cyperaceae

The leaf ultrastructure of NADP-malic enzyme type C4 species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics basically similar to the NADP-malic enzyme group of C4 grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess such particular membrane systems. The suberized lamella, probably a barrier for CO2 diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C4 acids. These ultrastructural features are discussed in relation to C4 photosynthetic function.

作物の群落構造と物質生産 : 受光およびCO_2拡散 : V.グレインソルガムの草高が群落光合成に及ぼす影響

The field experiment was carried out to study the effect of canopy height on CO_2 diffusion and canopy photosynthesis using the isogenic line of grain sorghum with different canopy height. Using the data obtained from the field experiment, CO_2 profile and canopy photosynthesis of grain sorghum were simulated. The results of the study are summarized as following; Canopy architecture of tall type grain sorghum was superior to the short type in all the factors concerning the CO_2 diffusion (wind speed at canopy surface, drag coefficient, attenuation coefficient of wind speed, mixing length and leaf width). High leaf photosynthetic rates (more than 100 mg CO_2/dm^2h) were observed under a field condition. The CO_2 profiles simulated by using these values of leaf photosynthesis coincided with CO_2 profiles measured in the canopy. Crop photosynthesis of tall type grain sorghum which has a LAI of 6.27 was 12% higher than that of short type which has a LAI of 5.21. Under the condition of a LAI of 6.0, the crop photosynthesis of tall type was 8% higher than short type canopy.