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Stefanie Peschel and Moritz Knoche

Frequency and distribution of microcracks in the cuticular membrane (CM) were monitored in cheek, suture, pedicel cavity and stylar regions of developing sweet cherry (Prunus avium L.) fruit using fluorescence microscopy following infiltration with a fluorescence tracer (1 to 2 min in 0.1% w/v acridine orange containing 50 mm 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.

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Bishnu P. Khanal, Rejina Shrestha, Leonie Hückstädt, and Moritz Knoche

thought to form in the hypodermal cell layer of developing apple fruit ( Meyer, 1944 ; Verner, 1938 ). The phellem appears at the fruit surface after the epidermis and cuticle are shed. The phellem’s suberized cell walls are responsible for the brownish

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Vladimir Orbović, Diann Achor, and James P. Syvertsen

trees following sprays of Kocide + zinc sulfate before flowering ( Peryea, 2000 ) implying that Cu can penetrate plant tissues. The plant cuticles are the primary barrier through which materials must pass to penetrate tissues ( Petracek et al., 1998

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Eric Curry

less irregularity among epidermal cells and reduced cuticle cracking in fruit treated with GA 4+7 than in untreated fruit. Skene and Greene (1982) recognized the relationship between microcracking in the cuticle and regions of russeting in ‘Cox

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Frank G. Bethea Jr., Dara Park, Andrew Mount, Nick Menchyk, and Haibo Liu

reduce water loss and heat exposure ( Kao and Forseth, 1992 ), and osmotic adjustment to reduce water potential ( Delauney and Verma, 1993 ). In addition to these drought tolerance strategies, cuticle augmentation in response to water deficit has been

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W. Robert Trentham, Carl E. Sams, and William S. Conway

-treated fruit. Lenticels seemed to become more compressed and less accessible in the highest Ca-treated fruit ( Fig. 2 ). Fig. 1. ( A ) Apple peel of fruit pressure-infiltrated with 0% CaCl 2 showing a normal hypodermis and cuticle vs. ( B ) a fruit

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Eckhard Grimm, Stefanie Peschel, Tobias Becker, and Moritz Knoche

walls compared with the mesocarp ( Glenn and Poovaiah, 1989 ), which indicates a role in stress containment. Third, the cuticle, as the outermost layer of the exocarp, is markedly strained in the course of development ( Knoche et al., 2004 ; Peschel et

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Judith Pozo, Miguel Urrestarazu, Isidro Morales, Jessica Sánchez, Milagrosa Santos, Fernando Dianez, and Juan E. Álvaro

vascular bundles. Solid silica is deposited in cell walls, cell lumens, the intercellular matrix ( Prychid et al., 2003 ), and a layer under the wax cuticle ( Kim et al., 2002 ; Yoshida, 1981 ). The silica in silica cells is deposited after the protoplast

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Bhaskar Bondada, Peter D. Petracek, and Jim Syvertsen

Recent interest in reducing nitrate levels in ground water has stimulated the re-examination of foliar application of urea on citrus trees. Because the cuticle is the primary barrier to foliar uptake, we examined the diffusion of 14C-urea through isolated citrus leaf cuticles. Cuticles were enzymatically isolated from leaves of the four youngest nodes (1 month to 1 year old) of pesticide-free grapefruit trees. The diffusion system consisted of a cuticle mounted on a receiver cell containing stirred buffer solution. Urea (1 μL) was pipetted onto the cuticular surface, and buffer solution was sampled periodically through the side portal of the receiver cell. The time course of urea diffusion was characterized by lag (time to initial penetration), quasi-linear (maximum penetration rate), and plateau (total penetration) phases. Apparent drying time was less than 30 min. Average lag time was about 10 min. The maximum penetration rate occurred about 40 min after droplet application and was about 2% of the amount applied per hour. Rewetting stimulated further penetration. The total penetration averaged about 35% and tended to decrease with leaf age. Dewaxing the second node cuticles by solvent extraction significantly increased maximum penetration rates (30% of the amount applied per hour) and total penetration (64%).

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David L. Ehret and Tom Helmer

Cuticle cracking (also known as russeting, rain checking, or shrink cracking) can significantly reduce the quality of greenhouse-grown tomatoes, adversely affecting appearance and shelf-life. In this study, the effects of several environmental and cultural factors on cuticle cracking were assessed. Plants (`Trust') were grown at one of three nutrient feed concentrations, with electrical conductivities (ECs) of 0.7, 2.0, and 4.0. Higher EC initially reduced the amount of cuticle cracking. Over 14 weeks, the amount of cracking increased in all treatments and the differences due to EC became less evident. Over this same interval, 24-h average relative humidity (RH) gradually increased and was correlated with the increase in cracking. Further analysis showed that this relationship was due primarily to an increase in nighttime RH. No other climatic conditions were related to cracking. To test the possibility that the increasing age of the crop also could have contributed to the increased cracking over time, two crops of different ages grown in the same greenhouse were evaluated for cuticle cracking. The older crop consistently showed a greater amount of cracking than the younger crop. Our data suggest that EC is useful in controlling cuticle cracking under some conditions, but that nighttime RH or possibly some factor associated with crop maturity may override the effects of EC.