ISHS Acta Horticulturae 487: VI International Symposium on Processing Tomato & Workshop on Irrigation & Fertigation of Processing Tomato
WHAT CONTROLS SUCROSE UNLOADING IN TOMATO FRUITS? |
| Authors: | M. Dorais, B. Nguyen-Quoc, H. N'tchobo, M. D'Aoust, C. Foyer, A. Gosselin, S. Yelle |
| Keywords: | invertase. Lycopersicon esculentum, sucrose phosphate synthase, sucrose synthase |
| Abstract:
Sucrose is one of the primary end products of photosynthesis in higher plants. It is also the major carbohydrate transported to sink tissues for plant development and storage. In developing tomato fruits sucrose metabolizing enzymes such as invertase, sucrose synthase and sucrose phosphate synthase have been suggested as regulating step for sucrose unloading. In order to test this hypothesis, a series of in vitro unloading experiments were performed in which the activity of sucrose degrading or synthesizing enzymes were modified. In the first set of experiments, the effects of acid invertase on the fruit unloading capacity were investigated by genetic tool using an invertase mutant (sucrose accumulator), and a high invertase line (hexose accumulator). Results from this study show that low levels of acid invertase did not affect significantly the tomato fruit unloading capacity at different stages of fruit development. Changes in sucrose synthase activity throughout fruit development, however, corresponded to different sucrose unloading capacities. Moreover, overexpression of sucrose phosphate synthase in tomato fruit increased sucrose synthase activity by 27%, and 70% more sucrose was unloaded in the transformed fruits (20 days after anthesis) compared to the untransformed controls. Similarly, we have recently conducted other in vitro unloading experiments with fruits in which the sucrose synthase activity was reduced using the antisense RNA technique. Unexpectedly, an almost complete inactivation of sucrose synthase activity (2% residual activity compared to control) had no significant effect on in vitro sucrose unloading. | |
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