Tansley Review No. 27 The control of carbon partitioning in plants

Abstract

Summary 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 storage capacity of the leaves and pathway tissues. However there appears to be little more than circumstantial evidence either that short 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 to photosynthesis 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‐controlled photosynthesis) 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).

Partitioning of 14C‐labelled photosynthate to developing nodules and roots of soybean (Glycine max)

“…Francisco & .\kao, 1993, Francisco & Harper, 1995, Recent results of Francisco & Harper (1995) suggest that inhibitory compound(s), synthesized in the leaf, control nodulation phenotype independently of the root, Francisco & Akao (1993) proposed a late-acting nodulation control mechanism that is apparently unrelated to autoregulation and is observed in wild type and in supernodulating soybean, Kosslak & Bohlool (1984) used different levels of shading to show that nodule number per plant and the intensity of the regulatory response were directly related to the amount of photosynthetically active radiation available to soybean. These results suggested a role for photosynthate partitioning in regulation of root nodule development, similar to that reported for regulation of axillary bud and inflorescence development (reviewed by Wardlaw, 1990), Available experimental evidence suggests that at least two distinct phenomena are in\ olved in regulation of nodulation in legumes. First, autoregulation of nodule initiation, which occurs early in the infection process, is apparently under physiological and genetic control, imposed by signal molecules that are normal products of bacterial (Takats, 1990;Caetano-Anolles & Bauer, 1988;re\iewed in Caetano-Anolles & Gresshoff, 1991(3) and plant (reviewed in GresshofT & Caetano-Anolles, 1991) genes.…”

Significant Changes in Cell and Chloroplast Development in Young Wheat Leaves (Triticum aestivum cv Hereward) Grown in Elevated CO2

“…Rapidly growing seedlings in elevated CO 2 growth conditions are typically "source limited" (Baysdorfer and Bassham, 1985;Wardlaw, 1990); therefore, additional carbohydrate resulting from enhanced CO 2 assimilation is immediately utilized for growth. In older (4 week old) wheat plants we have found much larger starch deposits in tissue grown in elevated CO 2 (data not shown).…”

Effects of partial rootzone drying and rootstock vigour on growth and fruit quality of 'Pink Lady' apple trees in Mediterranean environments

“…Water deficit may also alter partitioning between vegetative and reproductive sinks according to each organ's ability to attract photoassimilates. Seeds and fruits are in fact stronger sinks than shoot apices (Wardlaw 1990) and, under drought and limiting assimilation rates, vegetative growth should be reduced more and earlier than reproductive growth (Higgs and Jones 1991). In turn, contained vegetative growth may result in less shading of fruiting wood, better light distribution within the canopy, and less need for pruning.…”