Sugar Transport Mechanisms in Plant Systems

Plants rely on an intricate network of transport pathways to distribute photoassimilates from sites of synthesis (sources) to sites of utilisation or storage (sinks). Sucrose, the principal transport sugar in most vascular plants, moves cell-to-cell via two main routes: the symplastic pathway through plasmodesmata and the apoplastic pathway involving secretion into and retrieval from the cell wall continuum. At the cellular membrane level, dedicated transport proteins mediate sugar flux: sucrose transporters (SUTs or SUCs) actively load and unload sucrose into the phloem, while monosaccharide facilitators such as SWEETs and tonoplast-localised TMTs govern efflux, influx and compartmental allocation of hexoses. Regulation of these transporters is finely tuned by developmental cues, hormonal signals and environmental stresses, ensuring dynamic adjustment of source-sink relationships. Effective sugar partitioning underpins critical processes including seed filling, fruit ripening, tuber formation and vegetative growth. Advances in molecular genetics have revealed the modularity of transporter families, uncovering paralogues with tissue-specific expression patterns and dual substrate specificities. Understanding these mechanisms has profound implications for global food security and crop resilience, as modulation of transporter activity can enhance carbon allocation to yield components, improve nutritional quality and bolster stress tolerance in a changing climate.

Research from Nature Portfolio

Recent studies have demonstrated that certain SWEET transporters possess unexpected multifunctionality. In Arabidopsis, two members formerly characterised as sugar facilitators were shown to mediate cellular uptake of a key growth hormone, revealing a direct link between sucrose transporters and hormone distribution. Loss-of-function mutants exhibited defects in anther dehiscence and altered germination responses, which could be rescued by exogenous hormone application. These findings underscore the broader physiological roles of sugar transport proteins and highlight their contribution to long-distance signalling and developmental plasticity.

Sugar Transport Mechanisms in Plant Systems publication trend

The graph below shows the total number of articles in sugar transport mechanisms in plant systems across all publications each year (not limited to Nature Index journals).

Technical terms

Apoplast: The network of cell walls and intercellular spaces through which solutes can move outside the plasma membrane.

Symplast: The continuum of cytoplasm interconnected by plasmodesmata, allowing direct cell-to-cell transport of molecules.

Phloem loading: The process of moving photoassimilates into phloem sieve elements for long-distance transport.

SWEET transporter: A family of facilitative sugar transport proteins that mediate efflux and influx of mono- and disaccharides across membranes.

Sucrose transporter (SUT/SUC): Proton-coupled membrane proteins specialising in high-affinity uptake of sucrose into phloem cells.

Sink strength: The capacity of a plant organ to attract and accumulate photoassimilates, determined by metabolic activity and transporter expression.

References

1. AtSWEET13 and AtSWEET14 regulate gibberellin-mediated physiological processes. Nature Communications (2016).
2. SWEET11b transports both sugar and cytokinin in developing barley grains. The Plant Cell (2023).
3. Enzyme Repertoires and Genomic Insights into Lycium barbarum Pectin Polysaccharide Biosynthesis. Genomics Proteomics & Bioinformatics (2024).