Abstract
The partitioning of assimilates in fruits, which are economically important sink organs, is ruled by different physiological processes and affected by both environmental and agronomical factors. The bulk of the water and solutes, required for growth, is imported into fruits and seeds through xylem and phloem. In the stone fruits, five vascular bundles enter the base of the fruit, then dividing to supply either the flesh or the seed. The main sugars accumulated in stone fruits include fructose, glucose, and sucrose, along with other minor saccharides. The mechanisms of phloem loading in these fruit species have not been fully elucidated yet, but the available data hint either an apoplastic or a symplastic type or possibly a combination of both, depending on the species and the sugar considered. Similarly, phloem unloading mechanisms, elucidated for a small number of species, depend on genotype and developmental stage. Remarkably, key enzymes and transporters involved in the main sugars-conversion and transport pathways have received considerable attention. In stone fruit trees, the presence of an elevated number of fruits alters the source-sink balance, with a consequent intensification of competition among them and between vegetative and reproductive growth. The main environmental factors affecting this balance and the agronomical/artificial manipulations of source-sink relationships to achieve adequate fruit production and quality are reviewed.
Highlights
Growth and development in tree crops are combined processes in which the metabolic need of non-photosynthetic “sink” tissues, such as fruits, is balanced by the primary assimilation of photosynthetically active “source” tissues, such as mature leaves
Sugars are produced by fruit photosynthesis; over 90% of the assimilates required for peach growth are imported, and for cherries, this proportion is about 85% (Pavel and DeJong, 1993)
The model suggests a different utilization of sucrose and sorbitol from sap: almost all sucrose, which is not hydrolyzed into the apoplasm, would be stored in the vacuoles; on the other hand, sorbitol would be massively catabolized in the cytosol, representing the main driver for the respiration and the synthesis of structural compounds (Desnoues et al, 2018)
Summary
Growth and development in tree crops are combined processes in which the metabolic need of non-photosynthetic “sink” tissues, such as fruits, is balanced by the primary assimilation of photosynthetically active “source” tissues, such as mature leaves. Within a tree, fruits, which are strong sinks, compete for assimilates with each other, especially in case of high crop loads, as well as with vegetative organs, such as shoots, leaves, and roots (Pavel and DeJong, 1993; Ludewig and Flügge, 2013). For this reason, balance preservation between vegetative and generative growth, achieved by the artificial manipulation of source-sink relationships, can be essential to ensure acceptable fruit production and quality (Fischer et al, 2012). The partitioning of assimilates in economically important sink organs, such as fruits, is ruled by several processes, including photosynthetic rate, phloem loading, translocation throughout the phloem, phloem unloading, and uptake and metabolism of carbohydrates in sink organs (Patrick, 1997; Liesche and Patrick, 2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
