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S. Mark Goodwin, Christopher J. Edwards, Matthew A. Jenks, and Karl V. Wood

, the cutin component of the plant cuticle may also influence plant susceptibility to disease ( Jenks et al., 1994 ; Xiao et al., 2004 ). To date, however, the exact function of either cutin or waxes in rose pathogen resistance is unclear. A detailed

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Maalekuu Kissinger, Sharon Tuvia-Alkalai, Yavin Shalom, Elazar Fallik, Yonatan Elkind, Matthew A. Jenks, and Mark S. Goodwin

Fruit of pepper (Capsicum annuum L.) is hollow by nature, which limits its water reservoir capacity, and as such, small amounts of water loss result in loss of freshness and firmness, which reduce fruit quality, shelf life, and market value. In order to understand the basis for water loss from fruit, 10 pepper accessions with wide variation in water loss rate were used to study physiological and biochemical factors associated with postharvest water loss in ripe pepper fruit during storage. Postharvest water loss rate in ripe pepper fruit stored at 20 °C, and 85% relative humidity, was found to be associated with cell membrane ion leakage, lipoxygenase activity, and total cuticular wax amount. Total cuticular wax amounts were highest in the high-water-loss pepper fruit, and lowest in the low-water-loss fruit. However, total cuticle amount (isolated enzymatically and quantified gravimetrically), total cutin monomer amount, and the amount of individual cutin monomer and wax constituents (determined using gas chromatography mass spectrometry) indicated no direct association with postharvest water loss rates. Fruit fresh weight, pericarp weight, pericarp surface area, pericarp thickness, initial water content, and dry matter were highly associated with each other, but less so with water loss rate. Fruit of accessions displaying high fruit water loss rate matured and ripened earlier than fruit of accessions displaying low-water-loss rate. Cell membrane ion leakage and lipoxygenase activity were higher after storage than immediately after harvest. Pepper fruit total cuticle wax amount, lipoxygenase activity, and cell membrane ion leakage were directly related to postharvest water loss rate in pepper fruit during storage.

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D.S. Achor, H. Browning, and L.G. Albrigo

Young expanding leaves of `Ambersweet' [Citrus reticulata Blanco × C. paradisi Macf. × C. reticulata) × C. sinensis (L) Osb.] with feeding injury by third larval stage of citrus leafminer (Phyllocnistis citrella) were examined by light and electron microscopy for extent of injury and tissue recovery over time. Results confirmed that injury is confined to the epidermal layer, leaving a thin covering over the mine tunnel that consisted of the cuticle and outer cell wall. Wound recovery consisted of two possible responses: the production of callus tissue or the formation of wound periderm. The production of callus tissue developed within 3 days of injury when the uninjured palisade or spongy parenchyma below the injured epidermis produced callus tissue through periclinal or diagonal cell divisions. After 1 month, the entire epidermis was replaced by callus tissue. In the absence of secondary microbial invasion, this callus tissue developed a thick cuticle, followed by development of a covering of platelet wax after 4 months. Alternatively, wound periderm formed if the outer cuticular covering was torn before the cuticle had developed sufficiently to prevent the exposed cells from being desiccated or invaded by fungi, bacteria, or other insects. The wound periderm consisted of a lignified layer of collapsed callus cells, a suberized phellem layer, and a multilayered phelloderm-phellogen. Since there were always cellular collapse or fungi and bacteria associated with wound periderm formation, it was determined to be a secondary effect, not a direct effect of leafminer feeding.

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Moritz Knoche and Stefanie Peschel

initial increase (50 to 71 DAFB) was accounted for by both an increase in wax (50 mg·m −2 ·d −1 ; r 2 = 0.96, P ≤ 0.0188) and cutin deposition (88 mg·m −2 ·d −1 ; r 2 = 0.99, P ≤ 0.0048), and the net decrease thereafter (71 to 133 DAFB) by a

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Stefanie Peschel and Moritz Knoche

consistent with common biosynthetic pathways for synthesis of fatty acid based precursors of cutin monomers and wax constituents ( Peschel et al., 2007 ; Samuels et al., 2008 ). The overall deposition pattern of cutin and wax during fruit development was

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Fan-Hsuan Yang, David R. Bryla, and Bernadine C. Strik

matrix or cutin layer and an epicuticular wax layer. The latter, often referred to as the “bloom,” is deposited on and in the cutin matrix and contains long-chain alkanes, acids, alcohols, and esters ( Gülz, 1994 ). Without the wax, blueberries are prone

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P.C. Lee, A.G. Taylor, and T.G. Min

Sinapine leakage to detect seed germination potential on a single-seed basis in Brassica has been developed as a rapid test. In this test, sinapine leakage predicts that a seed is non-germinable; however, the major source of errors in this method are false-negative (F–)—i.e., the method predicted a seed was germinable because the seed did not leak, and it did not germinate. The sinapine leakage index (SLI) was used to asses the F– for any seed lot by dividing the number of non-germinable seeds that leaked sinapine by the total number of non-germinable seeds. Seed lots including cabbage, cauliflower, and broccoli (B. oleracea L., Captitata, Botrytis, and Italica groups, respectively) were used to examine the F–. The leakage rate as measured by T50, the time for 50% of heat-killed seeds to leak, was linearly correlated to SLI. Cabbage seeds were viewed by scanning electronic microscopy and leaking non-germinable seeds either had cracks or were shrunken. NaOCl pretreatment has been found to increase the rate of sinapine leakage and SLI. The mode of NaOCl was due to high pH altering the seed coat permeability. Chemical analysis was conducted on isolated seed coats for pectin, tannins, hemicellulose, cellulose, phenolic lignin, and cutin. It was found that the higher SLI (more permeable) lots contained lower amounts of cutin, suggesting that cutin may restrict the diffusion of sinapine through the testa.

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Zhiguo Ju and William J. Bramlage

Developmental changes in total cuticle and cuticular constituents were studied with `Delicious' fruit. Total wax (0.31 mg/cm2) and total cutin (0.54 mg/cm2, including carbohydrate polymers) were low in young fruit. They increased during fruit growth and reached 1.41 and 2.47 mg/cm2 of fruit peel at harvest, respectively. During fruit ripening at 20 °C, total cutin did not change, but total wax increased rapidly and reached 2.15 mg•cm-2 at 6 weeks. The increase of cuticular wax paralleled the increase of internal ethylene in fruit. Wax was separated by column chromatograph into four portions, hydrocarbons and wax esters, free alcohols, free fatty acids, and diols. More than half of the diols was ursolic acid. During fruit development, more hydrocarbons and diols accumulated in cuticle than free fatty acids and alcohols. During fruit ripening, all of the four portions increased, coincident with the climacteric rise in ethylene, but the increase rates of free fatty acids and alcohols were higher than those of other portions. Aminoethoxyvinylglycine (AVG, 220 mg•L-1) preharvest treatment inhibited internal ethylene synthesis to below 0.5 μL•L-1 during 6 weeks at 20 °C, and also inhibited wax accumulation. Ethephon (200 mg/L) preharvest treatment increased ethylene production and accelerated wax accumulation. α-farnesene accumulation coincided with increased internal ethylene and paralleled free fatty acid and alcohol accumulation.

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Zhiguo Ju and William J. Bramlage

Cuticle provides a barrier for secretory of volatile lipophilic metabolites like α-farnesene in fruit. The accumulation and oxidation of α-farnesene or the propagation of its oxidation products can be affected by the thickness, the constituents, and the structure of this cuticle. To measure the development changes of cuticle components, `Delicious' trees were treated separately with 250 ppm aminoethoxyvinylglycine (AVG) on 12 Sept. and 200 ppm ethephon on 19 Sept. Fruit were harvested on 28 Sept. and stored at about 20C for 6 weeks. Total wax in both treatment and control fruit at harvest was around 2.8 mg/f.fr.wt. It increased rapidly after 2 weeks and reached 8.4 mg/g fr.wt. in control fruit after 6 weeks, which paralleled increasing internal ethylene and accumulation of α-farnesene. Ethylene synthesis, α-farnesene, and total wax accumulation were enhanced by ethephon treatment and completely suppressed by AVG treatment during the whole period of storage. The cutin contents in fruit from treated fruit and the control were similar at harvest, and they remained constant during storage.

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Moritz Knoche, Bishnu P. Khanal, and Matej Stopar

The effect of four applications of gibberellin A4+7 [GA4+7 (10 mg·L−1 at 10-day intervals beginning with petal fall)] on water-induced russeting, formation of microcracks. and on fruit growth and deposition of the cuticular membrane (CM) was studied in developing ‘Golden Delicious’ fruit (Malus ×domestica Borkh.). Submerging developing apple fruit in deionized water for 48 h induced russeting in untreated control but not in GA4+7-treated fruit. Immersing in water during early fruit development, 19 days after full bloom (19 DAFB), resulted in more russeting than immersions occurring later (139 DAFB). Water on the outer surface of epidermal segments increased the frequency of microscopic cracks in untreated controls but to a lesser degree in GA4+7-treated fruit. The effect of GA4+7 on water-induced russeting and formation of microcracks was larger during early as compared with later stages of fruit development. Fruit treated with GA4+7 consistently had fewer microcracks as compared with non-treated control fruit. GA4+7 had no effect on amounts or rates of cutin or wax deposition, strain, or mechanical properties of the CM as compared with the non-treated control. Thus, the decrease in russeting and formation of microcracks in the cuticle of GA4+7-treated fruit must be accounted for effects on underlying epi- and hypodermal tissues.