11.3.1 Carbohydrate economy

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Enlarging fruit require carbohydrate to sustain cell division, enlargement and tissue specialisation. Only in later stages are carbohydrates typically retained as either starch or soluble sugars (Ho 1988). Soluble carbohydrate is mainly imported as photoassimilate, with only a minor contribution from local CO2 fixation, and reassimilation of respiratory CO2.

At peak growth rate, usually early summer, there is an intense flow of photoassimilate from mature leaves (sources) into rapidly enlarging fruit (sinks). Sugars generated by photosynthesis, along with amino acids and phosphate within the plant’s vascular network, move via phloem into enlarging fruits.