11.2.3 Cell differentiation

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Figure 11.4 Physical characteristics of apples change during growth and development with a notable increase in gas space to a maximum of around 0.1 mL gas mL-1 tissue at maturity, and corresponding decrease in cell wall mass to around 15 mg g-1 fresh mass. Cell surface area shows an early rapid decrease from around 340 cm2 mL-1 tissue.

(Based on Harker and Ferguson 1988)

Patterns of cell growth and differentiation in cell layers can influence the quality of mature fruit. For example, pepino fruit with a compact exocarp composed of tightly packed cells are less likely to bruise during postharvest handling than cultivars having large intercellular airspaces. As cell size increases during development, other accompanying characteristics also change, such as cell wall thickness, differentiation of specific cell types (e.g. sclereids) and formation of cell inclusions (oil, raphides). In feijoa and pear, development of sclereids in the mesocarp provides the characteristic gritty texture. As another example, juiciness of orange depends on prior differentiation of juice sacs in the endocarp (see Bain 1958 for anatomical development of citrus fruits).

Extent and distribution of airspaces are particularly important, affecting both fruit texture and physiological properties. For instance, in apples, airspace relative to fruit volume can double during development, while cell wall thickness and relative cell surface area both decline (Figure 11.4). Such changes affect gas exchange and diffusion of solutes through pericarp tissues due to increased tortuosity.