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  • Author or Editor: Mosbah Kushad x
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Seasonal variation in polyamines were evaluate during growth of fruit and seed of peach (Prunus persica L. cvs. Loring and Biscoe) starting at fruit set. In both cultivars, putrescine and spermidine increase significantly while spermine increase only slightly during the early stages of development then declined at the later stages. During pit hardening, polyamines in the flesh remained unchanged but their level in the seed continued to decrease. In both cultivars, polyamine levels corresponded to changes in fruit and seed sizes. when polyamines were vacuum infiltrated into commercially mature Biscoe fruits, flesh firmness, ethylene biosynthesis, and flesh color were significantly different from untreated tissue. The relationship between polyamines, seed development, and fruit development and ripening will be examined.

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Polyamines and the activities of their biosynthetic enzymes were evaluated during peach (Prunus persica L. `Biscoe') mesocarp (pulp) and seed growth starting at full bloom and until full fruit maturity at 14 weeks after full bloom (AFB). Mesocarp fresh mass exhibited a double-sigmoidal pattern characteristic of peaches. Seed fresh mass increased to a maximum of≈1 g at 4 weeks AFB then remained unchanged during the remaining weeks of sampling. Free putrescine, spermidine, and spermine levels were significantly higher in the flower bud, declined in the mesocarp tissue during the first 2 weeks AFB, then exhibited another increase between 2 and 6 weeks AFB. In contrast, conjugated spermidine and spermine levels were low in flower buds, then increased to their maximum level at 6 weeks AFB, then declined at full fruit development. Ornithine decarboxylase (ODC, EC 4.1.1.17) activity was high in flower buds (89.3 nmol·h-1·mg-1 protein) and in early stages of mesocarp development then declined to its lowest level (5.8 nmol·h-1·mg-1 protein) at full-fruit development. Arginine decarboxylase (ADC, 4.1.1.19) activity did not change during the first 6 weeks of mesocarp growth but declined later, reaching its lowest (1.95 nmol·h-1·mg-1 protein) at 14 weeks AFB. During the first 5 weeks AFB, ODC activity was 3.0- to 4.5-fold that of ADC activity; however, at full-fruit maturity (14 weeks AFB) the activities of both enzymes were similar. The slowdown in mesocarp growth during pit hardening between 6 and 9 weeks AFB did not change polyamines concentrations or their biosynthetic enzymes. Free spermidine and spermine levels declined during seed development; however, between 7 and 9 weeks AFB an increase in putrescine was observed. Similarly, conjugated putrescine increased substantially during seed growth reaching its highest level of 680 nmol·g-1 fresh mass at week 8 then declined at the later weeks, while conjugated spermidine and spermine peaked at week 10 to 1,169 and 2,148 nmol·g-1 fresh mass. ODC and ADC activities declined between 3 and 5 weeks AFB. However, a significant increase in ADC but not ODC activity in the seed tissue was observed during pit hardening between 6 and 10 weeks AFB. Based on the rapid increase in putrescine and ADC activity in the seed tissue, it appears that pit hardening may be a stress-related phenomenon. Data also suggest that polyamine levels in the mesocarp and seed tissue are independently regulated.

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Rye (Secale cereale) residues used in an alternative cropping system will affect nutrients, soil moisture, and soil temperatures. Each of these factors can affect tomato fruit quality. A field study was conducted comparing the effects of a rye cover crop, tomato variety, and N fertility on tomato fruit quality. In October, cereal rye was seeded at 100 kg·ha–1 to one-half of the plots. The rye was killed in mid-May by applying glyphosate at 1.1 kg·ha–1. Tomato seedlings were planted into the rye and bare-ground plots in late May. Four tomato varieties differing in cracking and soluble solids were used. There were two fertilizer regimes, no additional fertilizer, and N fertilizer applied broadcast before tomato planting, and as a sidedress based on soil tests, leaf analysis, and current recommendations. Tomato quality was evaluated based on 1) color as assessed using a Minolta chromameter, 2) cracking based on type and severity, and 3) soluble solids as determined by HPLC.

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5'-methylthioadenosine (MTA) nucleosidase (EC.2.2.2.28) and 5-methylthioribose (MTR) kinase (EC.2.7.1.100) activities were evaluated in `rin', `nor', and `Rutgers' tomato fruit during development and ripening. Changes in the activities of these enzymes were compared to ethylene biosynthesis. MTA nucleosidase and MTR kinase activities in `rin' and `nor' were ≈30% and 22%, respectively, lower than `Rutgers' during the first 2 weeks of fruit development. In `Rutgers', activities of these enzymes declined sharply until fruit maturity. Shortly before climacteric rise in ethylene synthesis, MTA nucleosidase, and MTR kinase activities increased, reaching a maximum level before peak ethylene synthesis then declined when fruit started to approach senescence. Whereas, `rin' and `nor' mutants exhibited no climacteric rise in ethylene synthesis and no change in MTA nucleosidase or MTR kinase activities, following their decline after 2 weeks of growth. A rapid increase in ethylene synthesis was observed when mature green `rin' and `nor' fruit were wounded. This increase in ethylene was paralleled by an increase in MTA nucleosidase and MTR kinase activities. However, increase in wound ethylene, MTA nucleosidase, and MTR kinase activities in `rin' and `nor' was ≈40% less than what we had previously reported in `Rutgers'. Relationship of MTA and MTR kinase activities to fruit growth, development, ripening, and natural and wound ethylene biosynthesis will be described.

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`Atlantic', `BelRus', `Kennebec', and `Superior' potatoes (Solarium tuberosum L.) were evaluated for ascorbic acid, soluble protein, and sugar content (reducing and nonreducing) at harvest, after 6 weeks of storage at 3C, and after 2 weeks of reconditioning at 25C. At harvest, ascorbic acid and soluble protein contents varied among the cultivars, with `Superior' containing the highest ascorbic acid (154 mg/100 g dry weight) and soluble protein content (46.4 mg·g−1 dry weight). Cold storage resulted in a drastic reduction (±50%) in ascorbic acid content in all four cultivars. Ascorbic acid also decreased during reconditioning of tubers, but the reduction was less than during cold storage. In contrast, soluble protein contents were not influenced significantly by cold storage or reconditioning, except for `BelRus' and `Kennebec', which had less protein after reconditioning. At harvest, glucose, fructose, and sucrose contents were at similar levels in all cultivars, except for fructose in `Kennebec', which was more than 2-fold higher. `Kennebec' also had a significantly lower specific gravity than the other cultivars. However, unlike the other cultivars, reconditioning of `Kennebec' tubers did not affect its specific gravity or total sugar content. Data suggest that `Kennebec's' poor processing quality may have resulted from a combination of low specific gravity and high total sugar content.

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Yukon Gold, a yellow-fleshed potato cultivar, was grown in Southwest Virginia and analyzed for ascorbic acid, soluble protein, and sugars (glucose, fructose, and sucrose) at harvest, after 6 weeks storage at 3 C, and following 2 weeks reconditioning at 25 C. Scanning and transmission electron micrographs were taken at each of the three stages to determine the effect of cold storage and reconditioning on the ultrastructure of amyloplast membrane. At harvest the tubers contained 154.0 mg/100 g ascorbic acid, 45.4 mg/g soluble protein, and 4.1 mg/100 g total sugar on dry weight basis. Cold storage resulted in more than 2.5 fold increase in ascorbic acid, between 4 and 9 fold increase in sugars, and a significant increase in soluble protein content. Reconditioning, however, decreased ascorbic acid, soluble protein and sugars. The ultrastructure of the amyloplast membranes remained intact throughout the storage period.

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A full-length cDNA (ArMY1) encoding myrosinase (β-thioglucoside glucohydrolase, EC 3.2.3.1) was cloned from horseradish (Armoracia rusticana) root. ArMY1 has an open reading frame of 1614 nucleotides with a deduced protein of 538 amino acids and molecular mass of 61.6 kD. ArMY1 shows highest overall amino acid identity (72%) with Arabidopsis thaliana myrosinase TGG2. ArMY1 mRNA signal of about 1.95 kb was detected in the leaves and roots of horseradish, but not in the leaves of broccoli. Heterologous expression of ArMY1 in baculovirus-infected Sf9 cells resulted in an immunologically active recombinant ArMY1 protein when probed with myrosinase-specific monoclonal antibody 3D7 with apparent mass 65 kD. Phylogenetic analysis showed that ArMY1 does not cluster with any of the current myrosinase subfamilies, i.e., the MA, MB, and MC subfamilies, and may represent a novel myrosinase subfamily in root tissue. This is the first report of cloning of myrosinase cDNA from horseradish root. It provides important sequence information that will enable further studies of myrosinase expression patterns and their interaction with myrosinase–binding proteins and other myrosinase-associated proteins.

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Superoxide dismutase (SOD: EC 1.1.15.1.1) and peroxidase (POD: EC 1.11.1.7) activities were evaluated during maturity, ripening, and senescence of `Red Spur Delicious' (Malus domestica Borkh.) apple fruits. SOD and POD activities did not exhibit uniform changes during fruit maturity; however, during fruit ripening, activities of both enzymes increased significantly. During fruit senescence, SOD activity continued to increase, while POD activity declined by 24% to 50%. Fruit maturity at harvest significantly affected SOD and POD activities during the progression of ripening and senescence. SOD activity was significantly higher during ripening and senescence of fruits that were harvested at full and over-mature stages than in fruits harvested at early mature stage. In contrast, POD activity was lower in fruits that were harvested at full and over-mature stages than in fruits harvested at early mature stage. Increase in SOD and POD activities during fruit ripening suggest that these enzymes are actively involved in scavenging free-radicals generated during this developmental stage. However, the decline in POD activity during fruit senescence suggest a possible disruption of the breakdown of H2O2 free-radicals. This disruption may have contributed to tissue senescence and the induction of a physiological disorder called senescence scald.

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Thirty horseradish (Armoracia rusticana Gaertn., Mey., & Scherb.) cultivars from eight countries in Europe and North America and from advanced lines developed at the Univ. of Illinois were evaluated for horseradish peroxidase (HRP; electrical conductivity 1.11.1.7, donor: hydrogen peroxide oxido-reductase) activity. Nearly 86% of the activity was present in the taproot and lateral roots and 14% in the leaf petiole, but there was no activity in the leaf blade. The 30 cultivars were divided into three groups with high (eight cultivars), medium (13 cultivars), and low (nine cultivars) activities [11.58 to 16.97, 7.19 to 9.79, and 2.88 to 6.91 μmol·min-1·g-1 fresh weight (FW), respectively]. The cultivars with the highest activity were 819-A from the Illinois and 810-A from Switzerland with 16.97 and 16.67 μmol·min-1·g-1 FW, respectively. The cultivar with the lowest HRP activity was 244-A from the United States with 2.88 μmol·min-1·g-1 FW. Cultivar 819-A also had the highest protein concentration (4.92 mg·g-1 FW). When HRP activity was expressed per milligrams of protein, cultivar 167-A, also known as `Bohemian', had the highest activity and cultivar 244-A had the lowest (5.35 and 0.83 μmol·min-1·mg-1 protein, respectively).

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