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Jorge M. Fonseca, James W. Rushing, and Robert F. Testin

The influence of temperature and O2 concentration on respiration and shelf life of fresh-cut watermelon was investigated. Product stored at selected temperatures from 1 to 30 °C showed increasing respiration and reduced shelf life with increasing temperature. Oxygen depletion and CO2 evolution were measured using a closed system method and rates of O2 consumption and CO2 production were computed. A mathematical model found to predict the CO2 production as function of temperature and O2 showed an elevated rate of CO2 production at about 14% O2 or lower. A modified atmosphere trial that compared product stored at 7 to 9 °C in air with product at either 14% or 8% O2 revealed increased respiration in the latter treatments, suggesting a relatively high anaerobic compensation point (ACP) at >14% O2. Our results suggest limited applicability of modified atmosphere packaging (MAP) for this product. Fresh-cut watermelon had extended shelf life and reduced respiration rate when stored at 1 to 3 °C and in >14% O2 atmospheres.

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Riccardo Gucci, John Everard, James Flore, and Wayne Loescher

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.

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R.M. Wheeler, K.A. Corey, J.C. Sager, C. L. Mackowiak, and W.M. Knott

Soybean plants [Glycine max (L.) Merr. cv. McCall] were grown from seed to harvest (90 days) in NASA's Biomass Production Chamber. The chamber provides approximately 20 m2 of growing area with an atmospheric volume of 113 m3. Photosynthesis and respiration rates of the stand were tracked by monitoring CO2 increase during the 12-h dark period and the subsequent drawdown to controlled set point (1000 ppm) when the lamps were turned on each day. Stand photosynthesis [under 875 μmol m-2 s-1 photosynthetic photon flux (PPF)] peaked at 35 μmol m-2 s-1 at 30 to 35 days after planting (DAP) and averaged 22 μmol m-2 s-1 throughout the life cycle. Dark period respiration peaked near 8 μmol m-2 s-1 at 30 to 35 DAP and averaged nearly 5 μmol m-2 s-1 throughout the life cycle. Prior to full canopy closure near 30 DAP, the light compensation point (LCP) for stand photosynthesis was lass than 100 μmol m-2 s-1 PPF; by 54 DAP the LCP had increasad to 175 μmol m-2 s-1. Stand transpiration rates peaked at 8.2 L m-2 day-1 at 40 to 45 DAP and averaged 4.3 L m-2 day-1 throughout growth.

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J.G. Norcini, P.C. Andersen, and G.W. Knox

Abbreviations: A, net CO 2 assimilation; Ci, intercellular CO 2 concentration; E, transpiration rate; GI, growth index; gs, stomatal conductance; LT, leaf ternperature; PE, pretreatment expanded; PPF, photosynthetic photon flux RE, recently

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Amanda M. Miller, Marc W. van Iersel, and Allan M. Armitage

Light and temperature responses of whole-plant CO2 exchange were determined for two cultivars of Angelonia angustifolia Benth., `AngelMist Purple Stripe' and `AngelMist Deep Plum'. Whole crop net photosynthesis (Pnet) of `AngelMist Purple Stripe' and `AngelMist Deep Plum' were measured at eight temperatures, ranging from 17 to 42 °C. Pnet for both cultivars increased from 17 to ≈20 °C, and then decreased as temperature increased further. Optimal temperatures for Pnet of `AngelMist Purple Stripe' and `AngelMist Deep Plum' were 20.8 and 19.8 °C, respectively. There was no significant difference between the two cultivars, irrespective of temperature. The Q10 (the relative increase with a 10 °C increase in temperature) for Pnet of both cultivars decreased over the entire temperature range. Dark respiration (Rdark) of both cultivars showed a similar linear increase as temperature increased. As photosynthetic photon flux (PPF) increased from 0 to 600 μmol·m-2·s-1, Pnet of both cultivars increased. Light saturation was not yet reached at 600 μmol·m-2·s-1. The light compensation point occurred at 69 μmol·m-2·s-1 for `AngelMist Purple Stripe' and at 89 μmol·m-2·s-1 for `AngelMist Deep Plum'. The lower light saturation point of `AngelMist Purple Stripe' was the result of a higher quantum yield (0.037 mol·mol-1 for `AngelMist Purple Stripe' and 0.026 mol·mol-1 for `AngelMist Deep Plum'). The difference in quantum yield between the two cultivars may explain the faster growth habit of `AngelMist Purple Stripe'.

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Abdul K. Janoudi, Irvin E. Widders, and James A. Flore

Laboratory, Michigan State Univ., East Lansing, MI 48824. 2 Associate Professor. To whom reprint requests should be addressed. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper

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Justine E. Vanden Heuvel and Joan R. Davenport

Carbohydrate supply has been hypothesized to limit fruit set in cranberry (Vaccinium macrocarpon Ait.), however the limitations to carbon gain throughout the season are currently unknown. These experiments investigated the effects of light, temperature, fruit presence, and defoliation on carbon production and partitioning in potted cranberry. Fruiting and vegetative uprights (short vertical stems which bear fruit biennially) reached similar asymptotes with respect to light response, but fruiting uprights reached saturation at a lower light intensity than vegetative uprights. Runners (diageotropic vegetative stems) had a lower asymptote, higher light compensation point, and greater rate of dark respiration than uprights. Temperature had little effect on net carbon exchange rate of uprights or runners. Before new growth, defoliation did not affect the concentration of total nonstructural carbohydrates in the vegetative uprights, or the partitioning of soluble carbohydrates to starch, even though uprights with lower leaf areas had higher net CO2 assimilation. At fruit set and again at fruit maturity, defoliation reduced total nonstructural carbohydrate concentration, while net CO2 assimilation was not affected. Carbohydrate production and partitioning within an upright was unaffected by the presence of a single fruit throughout the experiment.

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Chieri Kubota, Nihal C. Rajapakse, and Roy E. Young

`Green Duke' broccoli plantlets, which were ready for transplanting after 2 weeks of photoautotrophic (sugar free) culture under the conditions of 1100 μmol·mol–l CO2 (outside the vessel), 22 + 4C air temperature, and 140 μmol·m–2·s–1 photosynthetic photon flux (PPF), were stored for 6 weeks at 5C in darkness or in white, red, or blue light at 2 μmol·m–2·s–l PPF (light compensation point at 5C). Photoperiod was set at 24 hour/day during storage. Spectral quality significantly affected plantlet quality: stem length was longer and chlorophyll concentration of leaves was lower in red or in blue light than in white light or in darkness after 6 weeks in storage. Regardless of the spectral quality, light in storage maintained plantlet dry weight at a level comparable to that before storage; dry weight was reduced significantly in dark-stored plantlets. Spectral quality did not significantly affect the photosynthetic and regrowth potential of plantlets. All plantlets stored in light, regardless of light spectra, grew preferably and had similar dry weight and stem length after 9 weeks of transplanting to the greenhouse under natural light.

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Frank Williams, Alexis Barbarin, Donald Hauber, and Harish Ratnayaka

Poster Session 28—Stress Physiology 29 July 2006, 1:15–2:00 p.m.

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Cheryl R. Hampson, Anita N. Azarenko, and John R. Potter

1 Current address: Agriculture and Agri-Food Canada, Research Centre, Summerland, B.C., Canada V0H 1Z0. 2 Associate professor. 3 Research plant physiologist. Oregon Agriculture Experiment Station paper number 10962. This paper is a portion of the