Tansley Review No. 105. Sucrose biosynthesis in C₄ plants

Abstract

Summary 221

I. Introduction 221

1. The role of sucrose in plants 221

2. C₄photosynthesis 222

II. Pathway of sucrose synthesis in C₄plants 223

III. Control of sucrose synthesis in C₄plants 225

1. The diurnal cycle in C₃plants 225

2. The diurnal cycle in C₄plants 227

3. Abiotic stress and sucrose synthesis 230

4. Integration of sucrose synthesis with other metabolic pathways 232

IV. Future prospects 233

Acknowledgements 234

References 234

Sucrose has a central role in the metabolism of all higher plants. Here we discuss the location of sucrose synthesis in the leaves of C₄ plants, the control of flux through the pathway and its response to environmental conditions, and finally some of the prospects for the genetic manipulation of sucrose metabolism in C₄ plants. Much of our knowledge about sucrose synthesis in plants comes from C₃ species; it is evident, from those studies of C₄ species that are available, that there are many similarities between sucrose synthesis in C₃ and C₄ plants. However, some of the basic regulatory mechanisms common to both C₃ and C₄ plants seem to have been adapted for the specialized photosynthetic metabolism of C₄ plants. There are also some other important differences: for example, some C₄ species possess photosynthetic cells with little or no capacity for sucrose synthesis. For these reasons it is not always appropriate to extrapolate directly from C₃ to C₄ plants. Even where data are available from one C₄ species, usually maize, it should not be assumed that all C₄ plants are necessarily the same in every respect. Although C₄ plants constitute a small fraction of the plant kingdom as a whole, they include a disproportionate number of agriculturally important species. C₄ plants also have some advantages over C₃ plants for studies of the regulation of cell-specific gene expression and the control of metabolism. For these reasons we suggest that they are worthy of more attention by researchers.