Search Results

You are looking at 1 - 10 of 22 items for

  • Author or Editor: D. M. Pharr x
Clear All Modify Search

Mannitol represents a major carbon storage compound in celery petioles. Recently, a novel mannitol dehydrogenase was isolated from celeriac (Apium graveoiens L. var. rapaceum) root tips and partially purified to a specific activity of 210 μmol/h/mg protein. This NAD-dependent enzyme catalyzes the oxidation of mannitol to mannose. not fructose, and this is uniquely different from the mannitol oxidation in lower organisms. Data are presented that show that the enzyme is also present in celery (Apium graveoiens L. var. dulce) sink tissue. The product of the mannitol oxidation in celery was determined to be mannose. Previous studies suggested that differences in fertilizer concentration in the root zone of celery could alter carbon partitioning between mannitol and hexose sugars and change enzyme activities. In this study, plants were grown hydroponically at two different salt concentrations, E.C.=2.7 mS/cm and E.C.=6.0 mS/cm. A high mannitol to hexose ratio was observed in celery petioles of plants grown at high salt concentration, supporting the hypothesis that the salt environment might alter both mannitol and hexose pools in a coordinate way. Plants grown at both salt concentrations did not differ in root or shoot fresh weight. These data support the hypothesis that mannitol might be involved in osmoprotection by acting as a compatible solute. Mannitol accumulation in celery petioles might be, in part, regulated through a mannitol catabolizing pathway involving mannitol oxidation to mannose by the NAD-dependent 1-oxidoreductase, mannose phosphorylation by mannose kinase, mannose-6-P conversion to fructose-6-P by phosphomannose isomerase and further conversion to hexoses through a sucrose intermediate. The novel mannitol 1-oxidoreductase might therefore be a key enzyme in controlling mannitol levels in sink tissues.

Free access

Abstract

Tomato leaf and fruit chlorophyll content of a dark green mutant (dg) of Lycopersicon esculentum Mill cv. Manapal was compared to +/+ and +/dg (within ‘Manapal’) and another high pigment line (hp/hp) from 111. 1252. The mutant dg/dg contained the highest chlorophyll a and total chlorophyll in the exocarp and mesocarp and per unit leaf area. The exocarp and mesocarp of hp/hp contained intermediate chlorophyll concentrations. The mutant dg/dg and hp/hp contained a greater mesocarp chlorophyll b concentration than +/dg or +/+.

Open Access

Abstract

‘New Hampshire Tiny Dill’, a dwarf cucumber (Cucumis sativus L.) was more responsive to applied gibberellins (GA) in terms of hypocotyl growth than ‘Gynoecious 3’ and ‘Chipper’, standard vine types. The dwarf gave a more prolonged response to GA3. Treatment of all lines with GA4+7 significantly increased both the fresh and dry weight of the hypocotyl and hypocotyl unit, but not of the cotyledons.

Open Access

Abstract

Five cultivars of cucumber (Cucumis sativus L.) were found to vary in chlorophyll/cm2 and total chlorophyll/leaf. Gibberellin (GA) treatments did not change the total chlorophyll content per leaf but all lines responded more to GA4+7 than to GA3 in terms of increased leaf area and leaf fresh weight. Treatment with GA4+7 stimulated the rate of leaf expansion, but caused a reduction in chlorophyll/cm2.

Open Access

Abstract

Aqueous extracts of thawed, transverse slices of cucumber fruit (Cucumis sativus L.) gave reliable measurements of reducing sugar and total carbohydrate concentrations. Fruit fresh weight increased throughout a 20-day sampling period, averaging 0.6, 13.4, and 389 g at anthesis, 5, and 20 days after anthesis, respectively. Reducing sugar and total carbohydrate concentrations were highly correlated (r=.97), but were not correlated with fruit fresh weight (r=.40) or commercial fruit size (r=.52). Reducing sugar concentration at anthesis averaged 6.3 mg/g fresh weight and increased to a plateau averaging 22.7 mg/g from 5 to 20 days after anthesis. Reducing sugar concentration of 585 plant introductions and cultivars ranged from 7.1 to 52.8 mg/g and averaged 31.1 and 22.6 mg/g at 2 harvest dates.

Open Access

Abstract

In the paper, Measurement and Variation of Sugar Concentration of Pickling Cucumbers by J. D. McCreight, R. L. Lower, and D. M. Pharr (J. Amer. Soc. Hort. Sci. 103(2):145-147. 1978), the first sentence of the introduction should read “Bloating of commercially brined cucumbers results in a 5 million dollar loss each year to the U.S. pickle industry (6).”

Open Access

Two cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown with ambient or 1000 μl CO2/liter during Jan.-June 1987 and 1988. In both years, CO2-enrichment increased foliar deformation and foliar starch, but during the season, foliar starch levels decreased while deformation increased. `Laura' had more deformation, while `Michigan-Ohio' had higher foliar starch concentration. During an entire season, there was no significant relationship between foliar starch concentration and deformation severity. Foliar C exchange rates in the lower canopy were not affected by severity of deformation. Data from these experiments do not support the hypothesis that excess foliar starch is responsible for foliar deformation at elevated CO2.

Free access

Abstract

Plants of sweet potato (Ipomoea batatas (L.) Lam) were exposed prior to harvest to 1 week of warm-dry, warm-flooded, cold-dry or cold-flooded soil conditions. Roots harvested from the warm-flooded soil showed more rotting during curing than roots from the other treatments, and rotting continued during storage. Roots harvested from the cold-flooded soil rotted to a lesser extent during curing but rotted rapidly during storage. Roots harvested from the cold-dry soil showed no rotting during curing; however after 52 days of storage, the number of roots with rot increased sharply. Root respiration rates from cold-flooded, cold-dry, and warm-flooded soils were not significantly different, but those rates were much higher than the rate in roots from warm-dry soil. ‘Jewel’ had a lower respiration rate than NC 317. The cold treatments stimulated sprouting of sweet potato roots during storage. ‘Caromex’ showed the highest sprouting followed by ‘Jewel’, NC 317, and ‘Centennial’.

Open Access

Abstract

Harvested roots of 2 cultivars of sweet potato [Ipomoea batatas (L.) Lam.] were submerged in water to simulate flooding damage and changes in the concentrations of carbon dioxide, oxygen, and nitrogen were followed in the internal gas atmospheres. The internal gas was almost exclusively CO2, 72 hours after submergence.

Open Access

Abstract

A 24 or 48 hour soak in gibberellins (GA) did not influence the total germination of open-pollinated rabbiteye blueberry seeds (Vaccinium ashei Reade, cv. Tifblue). GA4+7 at 100-500 ppm stimulated early germination of seeds from the 2nd to 4th week after sowing, with the maximum effect occurring after 3 weeks. The 48-hour, GA4+7, 100 ppm treatment stimulated germination from the 2nd to 5th week after sowing. Stimulation of earlier germination by GA4+7 hastened seedling transplanting by 2 to 4 weeks. Germination of mature seeds (large, filled) was significantly higher than immature (medium-size, filled) or imperfectly (partially-filled) developed seeds. GA4+7 did not increase germination of immature or imperfectly developed seeds.

Open Access