Photosynthesis Assimilate Partitioning in Closely Related Lines of Rice Exhibiting Different Sink:Source Relationships

Closely related rice ( Oryza sativa L.) genotypes differing in sink to source ratios were evaluated for photosynthetic gas exchange characteristics, nonstructural carbohydrate content, leaf parameters, and yield components. Lines with a high sink to source ratio exhibited higher rates of carbon exchange per unit leaf area and accumulated lower amounts of nonstructural carbohydrates in vegetative storage tissues than did other lines. The line with the lowest sink to source ratio accumulated the most carbohydrates in storage tissues. The results suggest that the photosynthetic potential of rice was not fully realized, and that an increase in the sink to source ratio might result in higher yields. The low source lines had high specific leaf weights, however, and that factor may have been largely responsible for perceived increases in photosynthetic rates. When expressed on a unit leaf weight or unit leaf protein basis, low source lines did not necessarily exhibit high source activity. The results indicate that sink:source ratios can be altered genetically, and that such manipulations can affect plant yields.