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Control of photorespiration in plant leaves by rDNA technology: effects on plant physiology, agricultural productivity and water use efficiency


The agricultural productivity of crop plants like wheat, barley, potatoes and sugar beet is limited, not only by growing conditions but also by the performance of the photosynthetic apparatus. This is because these crops assimilate CO2 by the C3 pathway of photosynthesis and are subject to the limitations of the processes of photorespiration which lead to a loss of a proportion of the newly assimilated CO2 through the decarboxylation of glycine. In contrast, crops, like maize, which use the C4 pathway of photosynthesis do not lose CO2 in photorespiration. Conventional genetic approaches have not succeeded in alleviating the negative aspects of photorespiration in C3 plants. However, species with intermediate forms (C3/C4) of photosynthesis exist which appear to have improved photosynthetic characteristics and water use efficiency. Studies of these have given some ideas as to possible genetic modifications which might improve C3 plants. For example, the distribution of glycine decarboxylase within the leaf is changed such that the amounts in the mesophyll are much reduced and the amounts around the vascular tissue increased. Now that the major C3 crops can be transformed, it is possible to try to introduce such genetic changes into them using rDNA techniques and see if they improve crop performance. The project has this aim which will be achieved by meeting the following measurable objectives:
1 Production of transgenic potato and wheat plants with less glycinede carboxylase in the mesophyll cells of leaves.
2 Production of transgenic potato and wheat plants with greater expression of glycine decarboxylase in cells surrounding the vascular tissues of the leaf. 3 Combine the reduced expression in the mesophyll with increased expression in the vascular tissue within the same plant.
4 Measurement of the effects of the above changes on: a) photorespiration and photosynthesis; b) water use efficiency and c) field performance 5 From the above results, attempt to identify a strategy to obtain more productive plant with better water use, either from the transformants produced or by further experimentation.
The work will be carried out by a partnership of European laboratories each with specialist experience in one or more aspects of the project. The first group of transgenic plants are already available and the work planned has a high probability of being completed. The results should show whether or not modifying photorespiration is a suitable way to increase the productivity of important European crops such as potatoes and cereals.

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Rothamsted Experimental Station

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