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Wayne Loescher, Tad Johnson, Randolph Beaudry, and Sastry Jayanty

Sorbitol is the major carbohydrate translocated into apple fruit where it is normally metabolized to fructose. In watercored apple fruit tissues, however, the intercellular spaces become flooded and sorbitol content is consistently higher than in nonwatercored apples, suggesting a defect in sugar alcohol metabolism or transport. Our previous results have identified and characterized two sorbitol transporters, MsSOT1 and MsSOT2, in apple fruit tissues. Sorbitol transporter gene expression has been implicated in development of watercore with MsSOT expression diminished or absent in certain watercored fruit tissues. To explore this further, we have investigated the relationships between watercore, fruit maturation, fruit composition, and MsSOT expression in a number of apple cultivars that differ in watercore susceptibility. We also compared transporter expression between affected (watercored) and healthy parts of the same fruit and between watercored and nonwatercored fruits throughout the maturation and ripening processes. The MsSOT expression was often dramatically reduced in fruit tissues exhibiting watercore. Thus, in susceptible cultivars, maturing (ripening) fruit parenchyma cells lose the ability to transport sorbitol, and this in turn leads to sorbitol accumulation in the apoplastic free space and subsequent flooding of these spaces. These results are consistent with a relationship between watercore and sorbitol transport and also with a genetic susceptibility to the disorder.

Free access

Shiow Y. Wang and Miklos Faust

The glycolipids, phospholipids, and sterols were determined in normal and watercore-affected apple (Malus domestica Borkh. cv. Delicious). Fruit with watercore contained higher amounts of glycolipids, phospholipids, and sterols. The ratios of unsaturated to saturated fatty acids and (18:3) to (18:1 + 18:2) were lower in watercore-affected tissue than in normal tissue. The ratio of free sterols to phospholipids was higher, whereas the ratio of phosphatidylcholine to phosphatidylethanolamine was lower in watercore-affected apple. Membrane lipids were altered in watercore-affected fruit.

Free access

Shiow Y. Wang and Miklos Faust

Ethylene biosynthesis and polyamine content were determined in normal and watercore-affected apple (Malus domestics Borkh. cv. Delicious). Fruit with watercore produced more ethylene and contained higher amounts of putrescine (PUT), spermidine (SPD), 1-aminocyclopropane-1-carboxylic acid (ACC), and 1-(malonylamino) cyclo-propane-1-carboxylic acid (MACC). The activities of ACC synthase and ethylene-forming enzyme (EFE) in watercore-affected fruit were also higher than in normal fruit. The EFE activity in severely affected flesh was inhibited, resulting in ACC accumulation and low ethylene production. S-adenosylmethionine (AdoMet) was maintained at a steady-state level even when C2 H4 and polyamides were actively synthesized in normal and affected fruit.

Open access

Gary C. Marlow and Wayne H. Loescher

Abstract

Extraction and assay of sorbitol dehydrogenase (SDH) throughout fruit maturation of 3 apple (Malus domestica Borkh.) cultivars, watercore-resistant ‘Golden Delicious,’ occasionally susceptible ‘McIntosh’, and normally susceptible ‘Starkrimson,’ showed no relationship between susceptibility to watercore and extractable enzyme activity. There was, however, a relationship between increased SDH activity and onset of the climacteric as measured by ethylene and CO2 evolution, suggesting that SDH, like certain other enzymes, increases during maturation.

Free access

Hisashi Yamada, Hirokazu Ohmura, Chizuru Arai, and Makoto Terui

The influence of controlling temperature during apple (Malus domestica Borkh.) maturation on sugars, fruit maturity, and watercore occurrence was investigated in watercore-susceptible `Himekami' and `Fuji' apples. The incidence of watercore at 13/5 and 23/15C was greater than at 33/25C or ambient temperatures in `Himekami' apples in 1991 and was greater at 18/10C than at other temperatures in `Fuji' apples in 1990. In 1992, the extent of watercore increased as fruit temperature decreased from 28 to 14C and 23 to 9C in `Himekami' and `Fuji' apples, respectively. Watercore occurrence affected by fruit temperature was not related to fruit maturity, as judged by ethylene evolution. The effect of fruit temperature on sorbitol was relatively small compared with that on other sugars, and no relationship was found between watercore development and sugars. These results suggest that fruit temperature affects watercore expression independently of fruit maturity or sorbitol metabolism in the fruit in watercore-susceptible apple cultivars.

Open access

William J. Lord, Richard A. Damon Jr., and James F. Anderson

Abstract

A planting was established in 1964 and 1965 to evaluate the following ‘Delicious’ strains: ‘Red Prince’, ‘Jardine Red’, ‘Royal Red’, ‘Turner Red’, ‘Richared’, ‘Rogers Red’, ‘Gardner Red’, ‘Sturdeespur’, and ‘Starkrimson’, the last 2 being spur types. The strains have been evaluated through 1979. Leaf N, K, Ca and Mg levels varied among the strains but none was consistently different from another. The cumulative yield per tree from 1970 to 1979 was higher for all standard strains except ‘Red Prince’ than for the spur strains. Theoretical cumulative yield per hectare was highest for ‘Sturdeespur’ and significantly higher than all other cultivars with the exception of ‘Turner Red’. ‘Sturdeespur’ had the highest production efficiency. Watercore severity at harvest was inconsistent among the strains, but in 3 of 4 years fewer ‘Starkrimson’ fruits were affected.

Free access

F. Roger Harker, Christopher B. Watkins, Paul L. Brookfield, Mellisa J. Miller, Suzanne Reid, Phillippa J. Jackson, Roderick L. Bieleski, and Tim Bartley

Preharvest development and postharvest disappearance of watercore in `Fuji' apples (Malus ×domestica Borkh.) from a northern (Hawke's Bay, latitude 39° south) and southern (Otago, latitude 45° south) region of New Zealand were compared. A new method for quantifying watercore was developed. A photocopy was taken of the symptoms after each fruit was cut in half through the equator, and then the area of affected flesh (photocopies black) was measured using morphometric methods and compared to the area of unaffected flesh (photocopies white). Watercore was more severe and developed earlier in the season in Otago than in Hawke's Bay. In Otago, a block-type watercore predominated, disorder symptoms initially appearing in the tissues located at the junction of two carpels, while in Hawke's Bay a radial-type of watercore predominated, initially appearing in the tissues surrounding the coreline vascular bundles. Regression analysis identified that orchard and harvest date accounted for most of the differences in watercore symptoms and that the initial appearance of low levels of watercore was the best predictor that fruit would start to develop commercially significant levels of watercore. Incorporation of background color, internal ethylene concentration, starch pattern index, and firmness only slightly improved the regression coefficient. Watercore disappeared from the flesh during storage of fruit from both regions. Fruit from early harvests had the least severe symptoms, and the highest rates of watercore disappearance during storage. In fruit with more severe symptoms at harvest, its disappearance during storage was associated with an increase in fruit volume and air space, which occurred despite continuing mass loss. We suggest that during storage, the extracellular fluid associated with watercore symptoms is absorbed into the cells, and thus drives the increase in fruit volume.

Free access

Zhifang Gao, Sastry Jayanty, Randolph Beaudry, and Wayne Loescher

In apple (Malus ×domestica Borkh.), where sorbitol is a primary photosynthetic product that is translocated throughout the plant, accumulation of sorbitol in sink cells appears to require an active carrier-mediated membrane transport step. Recent progress in isolation and characterization of genes for sorbitol transporters in sour cherry (Prunus cerasus L.) and mannitol transporters in celery (Apium graveolens L.) suggested that similar transporters may be present in apple tissues. A defect in these transporters could also explain the occurrence of the fruit disorder watercore, characterized by the accumulation of fluids and sorbitol in the apoplasmic free space. Our objectives therefore included isolation and characterization of genes for sorbitol transporters in apple tissues and comparisons of expression of transporter genes, especially in various sink tissues including watercored and non-watercored fruit tissues. We have isolated and characterized two sorbitol transporter genes, MdSOT1 and MdSOT2. Sequence analyses indicated that these are members of the major facilitator transporter superfamily that gives rise to highly hydrophobic integral membrane proteins. Heterologous expression and measurement of sorbitol uptake in yeast indicated that these are specific and with high affinities for sorbitol, with Kms for sorbitol of 1.0 and 7.8 mm for MdSOT1 and MdSOT2, respectively. Sorbitol transporter expression was evident in all sink tissues tested with the exception of watercore-affected fruit tissues. Sorbitol accumulation in apple sink tissues thus involves an apoplasmic active membrane transport step and watercore results from a defect in that process.

Open access

M. W. Williams and H. D. Billingsley

Abstract

In 3 different seasons watercore began to develop in ‘Delicious’ fruit as the minimum temperatures dropped to near 4°C. In 1970 and 1971 watercore started to appear just before a sharp rise in sorbitol level occurred in the limb sap. In 1972 considerable watercore developed in the fruit before a significant increase in sorbitol was observed in the sap.

Open access

Hiroyuki Fukuda

Abstract

Internal breakdown in ‘Delicious’ apple (Malus domestica Borkh.) fruit was classified morphologically into 2 types. Type I breakdown was related closely to the intensity of watercore and type II breakdown was related to low Ca.