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Research Summary:  Photosynthesis annually converts two hundred billion tons of carbon dioxide into biomass worldwide.  Crop yields increased dramatically over the last century due in part to breeding and pruning practices that divert biomass from vegetative growth to harvestable organs such as tubers, fruits, and grains.  Biotechnology can further improve these gains through tissue-specific engineering of metabolic pathways.

Mature leaves are referred to as source tissues because photosynthesis produces a net surplus of sugar.  These sugars are transported to regions of growth and storage, termed sink tissues, along hydrostatic pressure gradients generated along the phloem vascular network.  In mature leaves, sugars accumulate in the phloem and water is drawn in by osmosis to establish a high hydrostatic (turgor) pressure (Fig. 1).  Conversely, in sink tissues, metabolites and water are used for growth, and the hydrostatic pressure is reduced.  This pressure differential results in a bulk flow of water and dissolved nutrients (i.e., the phloem sap) from source to sink tissues.  The extent of the gradient determines nutrient distribution; tissues with lower turgor pressure are stronger sinks, and receive a higher proportion of sap than lesser sinks.

In my laboratory, we seek to gain a deeper understanding of the phloem�s role in nutrient partitioning and plant growth and development by taking modern molecular approaches to classic physiological subjects.  Our interests in carbon partitioning include the role of sucrose transporters in long-distance transport, the transport efficiency of different naturally occurring sugars, and sugar metabolism at both the source and sink ends of the phloem transport system.  We are also interested in the role of long-distance signaling in plant development, and the regulation of phloem-specific genes that enable the phloem to function as it does.

Representative Publications:

Turgeon R, and Ayre BG (2005) Pathways and Mechanisms in Phloem Loading.  In NM Holbrook, MA Zwieniecki, and PJ Melcher, eds, Vascular Transport in Plants.  Elsevier Inc., San Diego, In Press.

Ayre BG, and Turgeon R (2004) Graft transmission of a floral stimulant derived from CONSTANS.  Plant Physiology; 135: 2271-2278.

Ayre BG, Blair J, and Turgeon R (2003) Functional and phylogenetic analysis of a conserved regulatory program in phloem of minor veins.  Plant Physiology; 133:1229-1239.

Ayre BG, Keller F, and Turgeon R (2003) Symplastic continuity between companion cells and the translocation stream: long-distance transport is controlled by retention and retrieval mechanisms in the phloem.  Plant Physiology; 131: 1518-1528.

This page was last updated on 10/04/06.