photosynthates

Photosynthates are the products of photosynthesis that are translocated or stored in plants. The term typically refers to the soluble sugars produced in photosynthetic tissues, mainly sucrose, along with smaller amounts of glucose and fructose, and to storage compounds such as starch that can be mobilized when needed. In many vascular plants, sucrose is the principal long-distance transport form moving through the phloem from photosynthetic source tissues (often mature leaves) to non-photosynthetic or developing sink tissues (roots, fruits, seeds, and growing shoots).

Synthesis and fate. Within chloroplasts, triose phosphates are produced during photosynthesis and are used either to synthesize starch for short-term storage or exported to the cytosol and converted into sucrose for translocation. Starch serves as a local, temporary store, while soluble sugars accumulate in the phloem for transport. Storage of sugars as starch occurs in plastids of leaves and storage organs, whereas soluble sugars can be stored temporarily in vacuoles or consumed in cells as needed.

Transport mechanism. Phloem transport relies on loading of sugars into phloem sieve elements at the source, creating an osmotic gradient that draws water into the phloem and generates a bulk flow toward sinks. Sugars are unloaded and metabolized or stored at the destination. The prevailing explanation for long-distance movement is the pressure-flow hypothesis. Loading can occur via apoplastic or symplastic routes, depending on species and tissue.

Ecological and physiological significance. Photosynthates link photosynthesis to growth, development, and storage, supporting root and shoot growth, fruit and seed development, and overwintering reserves. Allocation patterns vary with developmental stage, environmental conditions, and source–sink relationships.