Detached, wetted strawberries take up substantial water in the calyx region

In strawberry, surface disorders like ‘water soaking’, ‘cracking’ and ‘shrivel’ impair fruit quality of this high value crop. Water movement through the fruit surface is implicated a role in these disorders. The objective was to identify the pathways of water uptake and water loss (transpiration) and to identify factors affecting these flows. Water movement was quantified gravimetrically in detached fruit. Cumulative transpiration and uptake increased linearly with time. During ripening, fruit osmotic potential and water potential became slightly more negative. Rates of transpiration and water uptake and their corresponding permeances were constant during early ripening but increased as the fruit turned red. The permeance for osmotic water uptake was more than 10-times that for transpiration. Sealing selected regions of the fruit surface with silicone rubber allowed identification of the petal and staminal abscission zones in the calyx region and cuticular microcracks of the calyx region and receptacle as high flux pathways particularly for water uptake (osmotic). These results were confirmed by acridine orange infiltration and fluorescence microscopy. Increasing the relative humidity (RH) decreased the rate of transpiration, while increasing temperature increased both transpiration and water uptake. There was no effect of storing fruit (2 °C, ~ 80% RH) for up to 10 days. Our results identify petal and staminal abscission zones and cuticular microcracks as high flux pathways for water uptake

Water Soaking Disorder in Strawberries: Triggers, Factors, and Mechanisms

Water soaking is an important surface disorder of strawberries that limits unprotected field production. The objective was to identify the mechanism(s) of water soaking. Symptomatic fruit show pale, deliquescent patches of skin. This damage extends into the flesh. Numerous cuticular microcracks occurred in water-soaked areas. Water soaking occurred only if the skin was exposed to liquid water. Water soaking was more rapid when the cuticle had been abraded. Water soaking, anthocyanin leakage, and water uptake all increased with incubation time. There was a lag phase for water soaking and anthocyanin leakage, but not for water uptake. Susceptibility to water soaking increased with fruit ripening and mass. Incubation in isotonic PEG 6000 increased cuticular microcracking but decreased water soaking and water uptake. Incubation in hypotonic fruit juice (natural and artificial) increased water soaking incidence and severity but reduced water uptake. Incubation in dilute citric and malic acids increased plasma membrane permeability as indexed by anthocyanin leakage and increased water soaking. Thus, water soaking involves cuticular microcracking, localized water uptake, bursting of cells, and the release of organic acids into the apoplast. The damage propagates from cell to cell

Detached, wetted strawberries take up substantial water in the calyx region

In strawberry, surface disorders like ‘water soaking’, ‘cracking’ and ‘shrivel’ impair fruit quality of this high value crop. Water movement through the fruit surface is implicated a role in these disorders. The objective was to identify the pathways of water uptake and water loss (transpiration) and to identify factors affecting these flows. Water movement was quantified gravimetrically in detached fruit. Cumulative transpiration and uptake increased linearly with time. During ripening, fruit osmotic potential and water potential became slightly more negative. Rates of transpiration and water uptake and their corresponding permeances were constant during early ripening but increased as the fruit turned red. The permeance for osmotic water uptake was more than 10-times that for transpiration. Sealing selected regions of the fruit surface with silicone rubber allowed identification of the petal and staminal abscission zones in the calyx region and cuticular microcracks of the calyx region and receptacle as high flux pathways particularly for water uptake (osmotic). These results were confirmed by acridine orange infiltration and fluorescence microscopy. Increasing the relative humidity (RH) decreased the rate of transpiration, while increasing temperature increased both transpiration and water uptake. There was no effect of storing fruit (2 °C, ~ 80% RH) for up to 10 days. Our results identify petal and staminal abscission zones and cuticular microcracks as high flux pathways for water uptake

Swelling of cell walls in mature sweet cherry fruit : factors and mechanisms

Main conclusion: Swelling of sweet cherry cell walls is a physical process counterbalanced by turgor. Cell turgor prevents swelling in intact cells, whereas loss of turgor allows cell walls to swell. Abstract: Swelling of epidermal cell walls precedes skin failure in sweet cherry (Prunus avium) cracking. Swollen cell walls lead to diminished cell:cell adhesions. We identify the mechanism of cell wall swelling. Swelling was quantified microscopically on epidermal sections following freeze/thaw treatment or by determining swelling pressure or swelling capacity of cell wall extracts. Releasing turgor by a freeze/thaw treatment increased cell wall thickness 1.6-fold within 2 h. Pressurizing cell wall extracts at > 12 kPa prevented swelling in water, while releasing the pressure increased swelling. The effect was fully reversible. Across cultivars, cell wall thickness before and after turgor release in two subsequent seasons was significantly correlated (before release of turgor: r = 0.71**, n = 14; after release of turgor: r = 0.73**, n = 14) as was the swelling of cell walls upon turgor release (r = 0.71**, n = 14). Close relationships were also identified for cell wall thickness of fruit of the same cultivars grown in the greenhouse and the field (before release of turgor: r = 0.60, n = 10; after release of turgor: r = 0.78**, n = 10). Release of turgor by heating, plasmolysis, incubation in solvents or surfactants resulted in similar swelling (range 2.0–3.1 µm). Cell wall swelling increased from 1.4 to 3.0 µm as pH increased from pH 2.0 to 5.0 but remained nearly constant between pH 5.0 and 8.0. Increasing ethanol concentration decreased swelling. Swelling of sweet cherry cell walls is a physical process counterbalanced by turgor. © 2020, The Author(s)

Necked strawberries are especially susceptible to cracking

Fruit cracking is a commercially important disorder that reduces both quantity and quality of strawberries (Fragaria × ananassa Duch.). The objective was to identify the physiological mechanism of cracking and the factors affecting cracking. Cracking is more common in necked than in normal-shaped fruit. Most macroscopic cracks (‘macrocracks’) occur in the seedless neck. Large fruit is more cracking susceptible than medium size or small fruit. Macrocrack orientation is predominantly latitudinal in the proximal region of the neck and longitudinal in the mid and distal regions of the neck. The neck region of necked fruit has a thicker cuticle than the body of necked or normal-shaped fruit. The vascular bundles in the neck (seedless) are orientated longitudinally, while those in the body (with seeds) are both longitudinal and radial. Epidermal cells in the neck region are elongated longitudinally, with those in the proximal region of the neck being more elongated than those in the mid or distal regions of the neck. Cuticular microcracking was more severe in necked fruit than in normal-shaped fruit. The orientations of the microcracks matched those of the macrocracks, i.e., latitudinal in the proximal neck and longitudinal in the mid and distal neck regions. Following artificial incisions (blade), gaping was significantly more pronounced in necked than in normal-shaped fruit. Incubation of fruit in deionized water induced macrocracks in about 75% of fruit. Necked fruit cracked more than normal-shaped fruit. Most macrocracks were oriented latitudinally in the proximal neck and longitudinally in the distal neck regions. The results indicate cracking results from excessive growth strains which are further increased by surface water uptake

Water Potential, Osmotic Potential, and Cell Turgor in Developing European Plums

Neck shrivel is a fruit disorder of european plum (Prunus domestica L.). We investigate whether an asymmetrical distribution of osmolytes might explain the observations of a turgid stylar end and a flaccid stem end, in a selection of 17 plum cultivars sourced from two sites. The osmotic potential (ΨΠ) of the juices expressed from stem or stylar end fruit samples decreased (became more negative) during development. The cell turgor (ΨP) slightly increased during development up to 352 ± 42 kPa at 78 days after full bloom (DAFB) in the stem end and up to 331 ± 51 kPa at 92 DAFB in the stylar end, and then decreased. At maturity, ΨP averaged 22 ± 3 kPa in the stem end and 22 ± 4 kPa in the stylar end. These values are negligibly low compared with the very negative values of ΨΠ in the stylar end (−3188 ± 73 kPa) and stem end (−3060 ± 74 kPa). There was a transient gradient in ΨΠ between stylar end and stem end that almost disappeared by maturity. Marked differences in ΨΠ and its distribution were measured across 17 cultivars. In the majority (14), ΨΠ was more negative at the stylar end than at the stem end. A more negative ΨΠ in the stem was only detected in ‘Aprimira’, ‘Topfive’, and ‘Tophit’. Our results demonstrate that cell ΨP is very low and is essentially independent of ΨΠ in developing european plums. In most cultivars, ΨΠ in the stylar end is more negative than in the stem end. The absence of an axial gradient in ΨP and the small differences in ΨΠ between the stem and stylar end make both factors unlikely candidates for explaining neck shrivel

Calcium ions decrease water-soaking in strawberries

Water soaking is a common disorder of field-grown strawberries (Fragaria × ananassa Duch.). It develops when ripe fruit is exposed to rain. Here we investigate the effects of Ca on water soaking. Fruit was incubated in solutions of various Ca salts and the extent of water soaking quantified using a simple rating scheme. Exposure to CaCl2 (10 mM) decreased water soaking and anthocyanin leakage but had no effect on water uptake. The decrease in water soaking due to CaCl2 was not limited to a single cultivar but occurred in all cultivars examined. Incubating fruit in a chelating agent (EGTA) increased water soaking compared to the water control. Calcium salts of different acids varied in their effects on water soaking. Only CaCl2 reduced water soaking significantly. The chlorides of different cations, also varied in their effects on water soaking. Those of the monovalent cations had no effects on water soaking, while those of the divalent cations (CaCl2, BaCl2 and SrCl2) and of the trivalent cations (FeCl3 and AlCl3) were all effective in decreasing water soaking. Overall, CaCl2 decreased microcracking of the strawberry cuticle as compared to deionized water. Furthermore, CaCl2 also reduced the leakage of anthocyanins from flesh discs, irrespective of the osmotic potential of the incubation solution. Our results indicate that CaCl2 reduced water soaking by decreasing cuticular microcracking, by decreasing leakage of plasma membranes and, possibly, by increasing the crosslinking of cell wall constituents

Penetration of sweet cherry skin by 45Ca-salts: pathways and factors

Calcium is beneficial to sweet cherry physiology. The objective was to investigate factors affecting uptake of Ca into mature sweet cherry fruit through their skins. Penetration of 45Ca-salts was monitored using whole fruit or excised fruit skins mounted in diffusion cells. Penetration of 45CaCl2 into intact fruit and through excised skins increased with time. Sealing the pedicel/fruit junction decreased penetration, but sealing the stylar scar had no effect. There was little difference in permeances of the fruit skin to 45CaCl2, 45Ca(NO3)2, 45Ca-formate, 45Ca-acetate, 45Ca-lactate or 45Ca-propionate. Only 45Ca-heptagluconate penetrated at a slower rate. Increasing temperature markedly increased Ca-penetration. Penetration was most rapid at 35 °C, intermediate at 22 °C and slowest at 12 °C. Increasing relative humidity (RH) from 0, 28, 75 to 100% increased penetration of 45CaCl2, but penetration of 45Ca-formate was restricted to 100% RH. Increasing the RH from 50 to 100% at 96 h after droplet application had no effect on penetration of 45CaCl2, but increased penetration of 45Ca-formate. The results reveal that: (1) the fruit/pedicel junction is a site of preferential Ca-uptake and (2) Ca-penetration is limited by the mobility of the Ca ion in the dried-down droplet residue when the point of deliquescence of the applied salt exceeds the ambient RH

Xylogenesis and phloemogenesis in the flesh of sweet cherry fruit are limited to early-stage development

Water inflows into sweet cherry fruit occur via the xylem and the phloem vasculatures of the pedicel. The rates of these inflows are subject to marked changes during fruit development. The objective was to establish if, and when, xylogenesis and phloemogenesis occur in the fruit flesh (mesocarp) during fruit development. Fruit were cut in half and the median and the lateral bundles inspected by light microscopy. Fruit mass increased with time in a double sigmoid pattern. Xylogenesis and phloemogenesis were both limited to early fruit development (stage I). There were no consistent changes in the areas of either xylem or phloem after stage I until maturity (i.e., during stages II and III). The cross-sectional areas of xylem and of phloem in a bundle were both linearly related to total bundle area. Most of the increases (stage I) in bundle area (62%, r2 = 0.99***) were accounted for by increases in phloem area and about 35% (r2 = 0.97***) by increases in xylem area. A small percentage of the xylem area increase (about 4% of the total area of the bundle; r2 = 0.48***) was contributed by the appearance of intercellular spaces within the xylem. Our results suggest, that new xylem and phloem tissues are differentiated only during early development

Calcium decreases cell wall swelling in sweet cherry fruit

Swelling of epidermal cell walls decreases cell-to-cell adhesion and increases cracking susceptibility in sweet cherry. Ca is suggested to decrease cracking susceptibility by crosslinking of cell wall components and, possibly, by decreasing swelling. The objective is to test this hypothesis. The effect of Ca on swelling of anticlinal epidermal cell walls was quantified microscopically in vivo using excised skin sections and in vitro using extracted cell walls. After removal of turgor, cell wall thickness increased. Incubation in CaCl2 decreased cell wall thickness up to 3 mM CaCl2. At higher concentrations thickness remained constant. Decreased cell wall swelling in vivo also occurred with other salts of divalent and trivalent cations, but not with those of monovalent cations. Decreased swelling was due to the Ca cation, the anions had no effect. Ca also decreased swelling of cell walls that were already swollen. CaCl2 also decreased swelling of extracted cell walls in vitro. There was no effect on swelling pressure. The effect on swelling increased as the CaCl2 concentration increased. Chlorides of divalent and trivalent cations, but not those of monovalent cations decreased swelling in vitro. The decrease in swelling among the divalent cations was linearly related to the radius of the cation. The results indicate that Ca decreases cracking susceptibility by decreasing swelling