Abstract
It is generally thought that sucrose-phosphate synthase (SPS) can be a limiting enzyme of sucrose synthesis and photosynthesis. With soybean plants, Huber and Israel (1) showed that leaf starch contents were negatively correlated with the SPS activities (r = −0.71) and concluded that SPS is a key control point regulating the formation of not only sucrose but also starch. The partitioning of carbon between sucrose and starch is different among species (2). To our knowledge, transgenic plants over-expressing a maize SPS gene were made from only starch-formers such as tomato (3,4,5) and Arabidopsis (6). As demonstrated previously with those transgenic plants, over-expressing maize SPS increased the ratios of sucrose/starch accumulated in leaves (4,6). It is an open question whether the same effect is obtained in a sucrose-former, such as rice, or not. We investigated the effect of over-expressing a maize SPS gene on carbon partitioning in a sucrose-former, rice.
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