Characterization of Microcracks in the Cuticle of Developing Sweet Cherry Fruit

Abstract

<jats:p>Frequency and distribution of microcracks in the cuticular membrane (CM) were monitored in cheek, suture, pedicel cavity and stylar regions of developing sweet cherry (<jats:italic>Prunus avium</jats:italic> L.) fruit using fluorescence microscopy following infiltration with a fluorescence tracer (1 to 2 min in 0.1% w/v acridine orange containing 50 m<jats:sc>m</jats:sc> citric acid and 0.1% Silwet L-77, pH 6.5). These microcracks were limited to the cuticle, did not extend into the pericarp and were only detected by microscopy. Fruit mass and surface area increased in a sigmoidal pattern with time between 16 days after full bloom (DAFB) and maturity. The increase in frequency of fruit with microcracks paralleled the increase in fruit mass. During early development (up to 43 DAFB) the CM of `Sam' fruit remained intact. However, by 57 DAFB essentially all `Sam' fruit had microcracks in the pedicel cavity and ≈25% in the suture region with little change thereafter. At maturity percentage of `Sam' fruit with microcracks in cheek, suture, pedicel cavity and stylar end region averaged 23%, 25%, 100%, and 63%, respectively. Similar data were obtained for `Hedelfinger' (70% and 100% for cheek and pedicel cavity, respectively), `Kordia' (80% and 100%) and `Van' (100% and 100%). Generally, microcracks were most severe in pedicel cavity and stylar end region. Most of the first detectable microcracks formed above periclinal walls of epidermal cells perpendicular to their longest axis (72% and 92% in cheek and stylar regions, respectively). The other microcracks formed above the anticlinal walls were mostly oriented in the direction of the underlying cell wall. There was no difference in projected surface area, length/width ratio or orientation among epidermal cells below, adjacent to or distant from the first detectable microcracks in the CM. However, as length of microcracks increased the projected surface area of cells underlying cracks increased suggesting strain induced upon cracking of the CM. Permeability of excised exocarp segments in osmotic water uptake was positively correlated with number of stomata and number of microcracks in the CM. From our results we suggest that strain of the epidermal system during stage III of fruit growth is a factor in “microcracking” of the CM that may predispose fruit to subsequent rain-induced cracking.</jats:p>

Development of fruit quality traits and comparison of the fruit structure of two Vaccinium corymbosum (L.) cultivars

“…via the fruit pedicel vasculature, the pedicel fruit-junction (picking scar), through the cuticle, stomata, lenticels, microcracks, and the stylar scar fruit-junction (calyx scar). In turn, Peschel and Knoche (2005) in sweet cherry and Khanal et al (2011) in jostaberry, gooseberry, and black currant, have found that flower remnants on the fruit may serve as a preferential route for water uptake, since they contain small cracks through which water can transpire but also penetrate into the fruit. As in blueberries, floral remains in currants, jostaberry, and gooseberry dry up and are moved towards the fruit apex.…”

Water on the Surface Aggravates Microscopic Cracking of the Sweet Cherry Fruit Cuticle

“…Cracking is thought to result from increased turgor caused by rapid water uptake into the fruit (Andersen and Richardson, 1982;Considine and Kriedemann, 1972). Water uptake through the sweet cherry fruit surface occurs by different mechanisms along parallel pathways, including diffusion through the cuticular membrane (CM) (Beyer et al, 2005), viscous fl ow along the pedicel/fruit juncture , through guard cells or stomatal pores (Beyer et al, 2005), and through cracks in the CM (Peschel and Knoche, 2005).…”

“…Microscopic cracks in the CM, subsequently referred to as microcracks, frequently are observed on immature and mature sweet cherry fruit (Glenn and Poovaiah, 1989;Knoche et al, 2001;Sekse, 1995). Microcracks are minute fractures in the cuticle that do not traverse epidermal and hypodermal cell layers and are only detected by microscopy (Peschel and Knoche, 2005). Recent evidence suggests that formation of microcracks is closely related to strain of the CM (Peschel and Knoche, 2005).…”

Gibberellins Increase Cuticle Deposition in Developing Tomato Fruit

“…The decrease in CM mass per unit area was paralleled by a corresponding increase in elastic and plastic strain of the CM. Strain, in turn, was closely related to formation of microcracks in the CM (Peschel and Knoche 2005). These microcracks impair the barrier function of the sweet cherry fruit CM causing uncontrolled water uptake during rain events followed by fruit cracking (Glenn and Poovaiah 1989) and an increased incidence of fruit rot (Borve et al 2000).…”

“…This is a particular challenge for fruit that often are characterized by high rates of surface expansion until late in development. A mismatch of CM deposition and fruit surface expansion during development has been implicated in a number of surface disorders including fruit russeting and cracking (Bakker 1988;Williams et al 1989Williams et al , 1990; Knoche et al 2004;Peschel and Knoche 2005). Thus, there is considerable interest in understanding and manipulating CM synthesis and deposition during organogenesis, particularly in fruit bearing species.…”