Partitioning and Metabolism of Photorespiratory Intermediates

Abstract

Many external as well as internal factors control the partitioning of metabolites from source leaves to developing sinks. Initially, however all carbon in the plant and all energy used for the growth and development are derived through photosynthesis. With respect to net assimilation of CO₂, photorespiration (ie. the release of CO₂ in the light) is frequently viewed by breeders as an antagonistic process possibly even wasteful (1,2,3,4,5,6). However, in terms of maintaining whole plant growth in the natural environment photorespiration may have several homeostatic roles (7,8,9) which provide clear advantages to a plant facing adverse conditions. With the view to a better understanding of photorespiration and the role(s) it might preform, our studies have been focussed on the identification of the ‘end products’ of photorespiration at the cellular level and the relationship of their metabolism to the growth and development of the whole plant. As indicated in Fig. 1, the products of the glycolate pathway which actually leave the cell are CO ₂, the transport sugars (primarily sucrose), and amino acids (eg. glycine, serine, glutamate, glutamine).