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New Phytol. (1990), 116, 341-381

Tansley Review No. 27 The control of carbon partitioning in plants
BY IAN F. WARDLAW Division of Plant Industry, CSIRO, Canberra, ACT 2601 Australia {Received 27 February 1990; accepted 26 July 1990)
CONTENTS Summary I. Introduction II. General source-sink relationships 1. Local transport 2. Sink dominance and the supply of photosynthate {a) Hierarchy ofsinks (b) Improved canopy structure and light interception (c) The response to increased atmospheric COg concentrations 3. The timing of development 4. The response to stress Ill, Control at the source 1. Types of sources 2. Regulation in the leaf {a) Availability of carbon for translocation {b) Spatial and biochemical partitioning {c) Vein loading and vascular limitations (i) The path of transfer(ii) Uptake by the transport tissue (iii) Vein patterns {d) The response to carbon input (i) Photosynthetic rate (ii) The mobilization of leaf storage carbon (e) The response to daylength if) The response to demand 3 Genetic variation in net CO. exchange

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IV. The utilization ofphotosynthate: sink characteristics and limitations 1. Introduction 2. Vegetative tissues {a) Transport and transfer limitations {b) Metabolic limitations {c) Turgor and cell wall relaxation ( ^ Physical constraints 3. Fruit growth (^) General aspects {b) Cereal grains {c) Legume seeds 4. From flower to fruit V. Vascular constraints and temporary storage 1. Vascular links 2. Photosynthate retention andlateral transfer from the phloem 3. Source-sink proximity and vascular connections 4. Carrying capacity 5. The xylem as an alternative transport system 6. Temporary storage {a) The storage system {b) The utilization of stored carbohydrate (i) Cereals (ii) Trees (iii) Palms VI. Concluding comments Acknowledgements References

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This review reports on the processes associated with carbon transfer and metabolism in leaves and growing organs and the role of long-distance transport and vascular links in the regulation of carbon partitioning in plants. Partitioning is clearly influenced by both the supply and demand for photosynthate and is moderated by vascular connections and the storagecapacity of the leaves and pathway tissues. However there appears to be little more than circumstantial evidence either that shortANP 116


/ . F. Wardlaw

distance transfer of carbon within either the source or the sink, or that long-distance transport in the phloem, are limiting photosynthesis or growth directly. Although individual biochemical and physiological processes relating tophotosynthesis and growth may be well understood, the factors primarily responsible for the control of carbon partitioning in plants have not been clearly identified. There is a need for a greater understanding of organ initiation and development (source and sink formation and potential size), the clear identification of whether growth is sink or source limited (including possible sink-controlledphotosynthesis) and a detailed assessment of the role of storage in buffering developmental and environmental changes in sink and source activity. Also more information is needed on the role of hormonal and nutritional factors in regulating source and sink activity (organ interactions not directly associated with carbon transfer). Key words: Carbon partitioning, source, sink, vascular tissue,plant development.



In the simple unicellular green algae each cell is capable of carbon fixation by photosynthesis in the light, the uptake of nutrients, growth in size and reproduction. However the evolution and development of large land plants, in some cases nearly 100 m tall, has necessarily been accompanied by a division of labour between different cell types, tissues...
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