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  • Author or Editor: Wayne Loescher x
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Abstract

Relationships between leaf area per fruit and fruit weight, color, and soluble solids were modeled on spurs isolated following pit hardening on 2-year-old wood of ‘Bing’ sweet cherry (Prunus avium L.). Leaf area per fruit was found to be the largest measured source of variability in the three fruit quality parameters examined. Leaf area per fruit accounted for 66%, 36%, and 53% of the variability in fruit weight, fruit color, and soluble solids, respectively, at Pullman, Wash. Leaf area per spur accounted for 54%, 27%, and 28% of these same fruit quality parameters at Prosser, Wash. In all instances, there was a positive correlation between fruit quality and leaf area per fruit. Soluble solids content was most sensitive to increases in leaf area, followed by fruit weight and color. Leaf area per fruit is important because it represents photosynthetic potential. Ample productive leaf area is essential to producing high-quality sweet cherries.

Open Access

Diurnal fluctuations in soluble carbohydrates and starch were monitored in young (expanding), mature (first fully expanded), and old (nearing senescence) celery (Apium graveolens L.) leaves. In all tissues, mannitol and sucrose were the carbohydrates present in the highest concentrations. In old and young leaflets and their petioles, there was little change in levels of mannitol and sucrose in 26 hours. In mature leaflets, sucrose accumulated in the light and decreased in the dark; mannitol increased slightly in late afternoon. Starch concentration, although quite low, showed definite diurnal fluctuations in mature leaflets, but only small changes in young and old leaflets. Both sucrose and mannitol were present in mature petiole phloem tissues. Mannitol concentrations were high in the adjacent storage parenchyma tissue, but sucrose was almost undetectable. These data support earlier findings that sucrose is produced, translocated, and metabolized throughout the celery plant. Mannitol is also translocated, but also serves as a major storage carbohydrate in leaf tissues, especially petiole parenchyma. Starch serves as a minor short-term storage compound in leaflets.

Free access

Soil salinization is an increasing problem worldwide and is often intensified by irrigation. Unfortunately, few new crop cultivars have been developed resistant to saline soils, a consequence, in part, of the complexity of plant responses to salt stress. There are now, however, several non-traditional options to improving salt tolerance as a result of recent progress in better understanding the mechanisms involved. These mechanisms include 1) exclusion of Na+ and Cl from plant tissues; 2) inclusion of these ions in inert compartments or tissues; and/or 3) some means of osmotic adjustment with solutes that are compatible with the metabolic machinery of the cell. Although there are very few horticultural examples, several lines of evidence indicate that reductions in salt sensitivity through exclusion or inclusion can be achieved by single gene modifications of the ion transport system. Similarly, single genes resulting in osmotic adjustment with solutes compatible with the metabolic machinery of the cell have resulted in significant increases in salt tolerance. Recent advances in sequencing, use of quantitative trait loci, and marker-assisted selection promise to provide other options for improving salt tolerance.

Free access

Abstract

Nonstructural carbohydrates of sweet cherry (Prunus avium L. ‘Bing’) changed dramatically both qualitatively and quantitatively during the year. In perennial tissues, total nonstructural carbohydrates (TNC) were highest at leaf abscission. TNC increased sharply in spurs at budbreak, but, in other perennial tissues, reserves decreased with or before budbreak. TNC in all but spurs were least, e.g., 2% to 4% of fall levels, shortly after full bloom, but then immediately began to increase. Accumulations slowed during the last 4 to 6 weeks of fruit growth and then increased after harvest. Prebloom decreases and postbloom increases occurred earlier in 1- and 2-year-old shoots when compared to trunk or root tissues. Starch was the most common storage material. During winter, interconversion of starch and soluble carbohydrates in wood of the trunk and 1- and 2-year-old shoots was apparent. Sucrose was the predominant soluble carbohydrate during dormancy, but sorbitol dominated during active growth. Raffinose was present only during dormancy, and inositol only when leaves were present. Because sweet cherry flowers and fruits early, carbohydrate reserves could critically affect productivity.

Open Access

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.

Open Access

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

Abstract

Mesocarp development of peach [Prunus persica (L.) Batsch cv. Redhaven] as measured by fresh weight and size increase, progressed along a double sigmoid curve which was reflected in the activity of extractable wall-associated α- and β-nitrophenylgalactosidases. Enzyme activities, both on protein and dry weight basis, rose rapidly during early fruit development, leveled off, then again rose rapidly at maturation. There was more α-nitrophenylgalactosidase activity than β-nitrophenylgalactosidase activity throughout development. Increases in both galactosidases followed rather than preceded increases in size. The final increases were, however, well correlated with fruit maturation.

Open Access

In Michigan boron (B) deficiencies in sour cherry have resulted in routine use of B sprays to enhance fruit set and increase fruit yield. However, field observations indicate that high B levels are associated with premature softening, making fruit unacceptable for processing. Our fertilization studies show that fruit B levels are higher, but B generally has little or no effect on fruit size, maturity, color, or pull force. However, at some locations, B applications increase the number of soft fruit, especially when harvest is delayed well after the optimum maturity date (as indicated by pull force). B-induced yield increases can be achieved without inducing excessive fruit softening by careful monitoring of fruit maturation and prompt harvest. Leaf and fruit B levels will be presented.

Free access

Photosynthetic rates (A) in celery-(Apium graveolens L.) and other polyol-synthesizers are sometimes high for C, species. In celery such rates have been related to a low CO2 compensation point typical of C4 and C3-C4 intermediate spp, although other data show celery photosynthesis as typically C3 Therefore, celery gas exchange was here reanalyzed, and while A was high (CO2 assimilation rates were 21.2 and 27.6 μ mol m-2s-1, average and maximum, photosynthesis was otherwise C,: CO, comp pt of 3.5-5.0 Pa, carboxylation efficiency of 0.99 μmol CO2m-2s-1Pa-1, light comp pt of 8-36 μ mol photon m-1s-1, optimum temp of 22-27°C for Amax. High A may relate to a capacity to synthesize both mannitol and sucrose. 14C pulse-chase studies, with different A obtained by imposing light gradients across opposite leaflets, showed 1-10% increases in mannitoll sucrose labelling. Higher A may reflect carbon partitioning into mannitol, agreeing with a hypothesis that polyol synthesis effectively recycles reductant in the cytosol.

Free access

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.

Free access