Metabolism and transport of carbon in legume nodules under phosphorus deficiency

Abstract

Phosphorus (P) is an essential element for plant growth but is largely unavailable for root uptake due to the formation of insoluble complexes. Therefore, P deficiency is a wide-spread agricultural dilemma. However, in addition to P, nitrogen (N) and carbon (C) metabolisms are intricately linked to plant physiological events and are major determinants in the plant and nodule responses to P deficiency. These responses can be measured in terms of growth, photosynthesis, and respiration. It has been shown that during P stress, plant growth also affects the C requirement of biological N2 fixation (BNF), and this has been proposed as a means of BNF regulation. Furthermore, the sink effect of nodules, at various levels of developmental and functional stages, has been observed via alterations in photosynthesis and respiration. The photosynthetic and respiratory C costs of BNF and nodule growth make considerable contributions to the overall C budget of the symbiosis. However, the use of overall C budget may mask the separate allocation of C to above and belowground organs during P deficiency. Moreover, the division of respiratory energy toward new tissue growth and nutrient acquisition may not be evident in the overall C budget. In this chapter, we review the recent contributions made in the arena of C metabolism of nodules during P stress and will aim to gain a better understanding of the underlying physiological and transcriptional events which give rise to changed in the C budget and allocation.