Distribution of C4 photosynthesis in the plant kingdom Taxonomic and life form distribution

From a floristic survey of photosynthetic pathway in the plant kingdom, it is difficult to conclude that C4 photosynthesis is the superior syndrome. Of the 280,000 terrestrial plant species, about 7,500 are C4, or only 3 of the land plant flora (Sage et al 1999a). By contrast, between 20,000 and 30,000 CAM (Crassulacean acid metabolism) species are spread over a greater range of taxonomic groups than C4 plants (Smith and Winter 1996). As with C4 plants, most C, plants are tropical, and the...

Ideotype breeding

Ideotype breeding aimed at modifying the plant architecture is a time-tested strategy to achieve increases in yield potential. Thus, selection for short-statured cereals such as wheat, rice, and sorghum resulted in a doubling of yield potential. Yield potential is determined by the total dry matter or biomass and the harvest index (HI). Tall and traditional rice varieties had an HI of around 0.3 and total biomass of about 121 ha-1. Thus, their maximum yield was about 41. This biomass could not...

What governs yield The yield equation

A systems analysis approach to the complex issues surrounding yield limits can help in deciding what factors determine yield and their relative importance. It will be used here to derive some simple rules of thumb and provide an overview of the important features of a high-yielding rice system. After that is done, each of the features identified will be analyzed briefly with respect to its contribution to yield. Initially, the mass balance of the whole crop in terms of its inputs and outputs is...

Longterm trends in rice prices and yields

Since the Green Revolution began in the mid-1960s, rice prices have fallen in real terms (i.e., after adjusting for inflation) and the productivity of rice land has increased dramatically. Both of these developments have made important contributions to poverty alleviation in Asia. From 1950 to 1981, the price of rice on the world market averaged approximately US 860 r1 (constant 1998 prices). From 1985 to 1999, however, prices averaged about US 327 t ', a decline of 62 (Fig. 1). This is a...

Photosynthate distribution into roots

Since one unit of internode organs, namely, leaf, axillary organ, and root, can reproduce the whole plant, it is defined as a phytomer or phyton (Evans and Grover 1940. Kawata et al 1963) (Fig.l). However, since the leaf-upper adventitious root and the branch-lower adventitious root in the phytomer belong to a different phyllotaxy. it is difficult to explain the photosynthate distribution within a phyton or between phytons. Therefore, we propose a node unit hypothesis. Table 1. Yields (g m 2)...

Radiation conversion factor

The radiation conversion factor (RCF also called radiation-use efficiency, RUE) links the biomass produced by a crop to the radiation intercepted (Monteith 1977, and see reviews in Russell et al 1989, Mitchell et al 1998. and Sinclair and Muchow 1998). We avoid the word efficiency, which means a dimensionless quantity with maximum value of 1, because we wish to work in biomass per unit intercepted radiation (g MJ') The RCF is a mathematical conversion factor between two measurable variables the...

Leaf anatomy

Leaves possessing the C4 pathway stand out because of their Kranz anatomy, recognized by Haberlandt (1914) long before the biochemical significance was known. Around each vascular bundle is a wreath of cells, the bundle sheath, where CO is concentrated and Rubisco is located. Surrounding the bundle sheath are mesophyll cells that first fix the C02 into C4 acids. For the successful operation of C4 metabolism, it is necessary to differentiate this special anatomy. Given that the C4 pathway has...

C3 versus C4 photosynthesis in rice ecophysiological perspectives

C4 photosynthesis confers substantial benefits upon herbaceous plants in tropical environments, most notably in high-light habitats with frequent drought, heat, and salinity stress. In flooded situations, It is less beneficial, for reasons that are not clear. Conditions In wetlands may not enhance C02 assimilation rates of C plants to the degree needed to suppress C3 competitors alternatively, wetland C3 plants may be well adapted for marshy environments for reasons unrelated to photosynthetic...

Forest and marsh grass ecology in reference to photosynthetic pathway

To understand why rice is successful in flooded situations, it is useful to evaluate the mechanisms contributing to the success of C, grasses in tropical environments. This can be done with some certainty for forest grasses, but the situation with marsh grasses is less clear. The experience with forest grasses, however, provides some insight that may help explain the relative success of C3 marsh grasses at low latitude. The failure of C4 species to dominate the low-light habitats within...

Future trends in rice demand

Will the trend of lower prices and higher yields continue In the case of prices, the outcome will depend on both supply and demand. In the next 20 years, future demand for rice will Fig. 3. Trends in real retail prices in India and Bangladesh. Sources of raw data IRRI (1995, 2000). Fig. 3. Trends in real retail prices in India and Bangladesh. Sources of raw data IRRI (1995, 2000). Fig. 4. Paddy rice yields in Asia. Source of raw data FAO (1999). Fig. 4. Paddy rice yields in Asia. Source of raw...

Nitrogen cost of C4 versus C3 photosynthetic pathways

In this section, we will assemble data to illustrate the nitrogen cost of the soluble enzymes directly involved in CO, assimilation. In C3 leaves, Rubisco dominates the profile of leaf protein, typically representing one-third of the soluble protein. The remaining 11 enzymes of the photosynthetic carbon reduction (PCR) cycle account for only another 10 of the soluble protein (Evans and Seemann 1989). The enzymes necessary for the C4 cycle are also present in C3 leaves, but at low levels, and...

High expression of maize C4specific genes in rice

Some attempts have been made in the past to increase the activities of C4 photosynthesis enzymes in C, plants through recombinant DNA techniques Hudspeth et al 1992. Kogami et al 1994, Gehlen et al 1996 . However, the activities of the C4 enzymes in transgenic C, plants were low, and consequently no significant impact on the physiology of photosynthesis was observed. The introduced genes used in these studies mainly consisted of cDNA clones encoding the C4 Fig. 4. Hypothetical models that...

The contribution of poverty alleviation

Rice is the dominant staple food of Asia, accounting for more than 70 of caloric Intake In some countries. Furthermore, Asia Is home to approximately 70 of the world's 1.3 billion poor, and the most severe malnutrition in the world occurs in South Asia. These considerations mean that rice research has a key role to play In global poverty alleviation. Rice research contributes to poverty alleviation through several pathways, and these contributions benefit both producers and consumers. The...

Singleleaf photosynthesis

Rice is classified as a C, plant despite isolated claims of C4 characteristics Hegde and Joshi 1974, Imaizumi et al 1990 . The value of Pn measured under optimal conditions has become increasingly higher in recent years as the accuracy of measuring instruments has been improved Matsuo et al 1995 . Maximum Pn under saturated light ranges from 25 to 32 imol m 2 s ' Yoshida 1981 and 40 imol m 2 s ' was measured recently in rice leaves at IRRI. The value of Pn depends on leaf morphology and...

Photosynthesis and yield potential

Various physiological selection criteria have been tried in plant breeding including P , C02 compensation point, Km C02 of Rubisco, photorespiration, SLA, and mesophyll cell size. However, breeding for increased yield potential by improving photosynthesis has resulted in little or no success Gifford and Jenkins 1982 . Although genetic variation in Pn has been reported in rice, the relationship between photosynthetic capacity and biomass production is poor McDonald et al 1974 . Zelitch 1982...

Canopy photosynthesis

Canopy photosynthesis is difficult to measure because of carbon dioxide fluxes in the aerenchyma of the plant and from the soil and water. The highest canopy net photosynthetic rate CPn is generally observed at 1000-1100 Dingkuhn et al 1990b . Maximum CPn reaches 45 to 50 imol m-2 s_1 on a clear day for a high-yielding rice cultivar grown under favorable conditions Dingkuhn et al 1990b . On a seasonal basis, CPn reaches a maximum between panicle initiation and the booting stage when LAI is the...