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Sasmita Mishra, Scott Heckathorn, Jonathan Frantz, Futong Yu, and John Gray

boron (B) deficiency on net photosynthesis (P n ) ( A–B ), carboxylation efficiency (CE) ( C–D ), and PSII efficiency (F v /F m ) ( E–F ) in geranium plants grown under low- or high-light conditions (100 or 300 μmol·m −2 ·s −1 PAR ). Plants were

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Lingyun Yuan, Yujie Yuan, Shan Liu, Jie Wang, Shidong Zhu, Guohu Chen, Jinfeng Hou, and Chenggang Wang

and accelerated senescence. The photosynthesis in C 3 plant is more sensitive to HT, especially the photosynthetic apparatus ( Wahid and Rasul, 2005 ). HT differently affects the stability of many proteins and membrane system and alters the efficiency

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Francesco Montesano and Marc W. van Iersel

of CO 2 inside the leaf, conversion of gaseous CO 2 to dissolved HCO 3 − , light and dark reactions of photosynthesis, and potential feedback inhibition of photosynthesis. Carboxylation efficiency, an indicator of Rubisco activity, was determined

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Joshua K. Craver, Krishna S. Nemali, and Roberto G. Lopez

radiation, CO 2 is a limiting input of photosynthesis ( Tremblay and Gosselin, 1998 ). An atmosphere enriched with CO 2 is associated with increased carbon fixation rate, water-use efficiency, and nitrogen-use efficiency ( Arp, 1991 ). As energy

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Xuan Liu and Donald L. Suarez

g ( A and B )], nonstomatal limitation to photosynthesis [ L m ( C and D )], and photosynthesis carboxylation efficiency [ α ( E and F )] to irrigation water salinity at the vegetative growth and pod growth stages [days after planting (DAP

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Lailiang Cheng and Leslie H. Fuchigami

119 ORAL SESSION 31 (Abstr. 597–603) Photosynthesis & Carbon Metabolism–Fruits/Nuts

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John W. Moon Jr.

179 ORAL SESSION (Abstr. 715-722) CROSS-COMMODITY PHOTOSYNTHESIS

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Lailiang Cheng, Sunghee Guak, and Leslie H. Fuchigami

76 ORAL SESSION 12 (Abstr. 078–083) Photosynthesis

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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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F. Christine Pettipas, Rajasekaran R. Lada, Robert Gordon, and Tess Astatkie

Increasing temperature as a result of global climate change is expected to exert a great influence on agricultural crops, possibly through effects on photosynthesis. Response to temperature of leaf gas exchange parameters of carrot (Daucus carota L. var. sativus) cultivars Cascade, Carson, Oranza, and Red Core Chantenay (RCC) were examined in a controlled growth room experiment. Leaf net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were measured at temperatures ranging from 15 to 35 °C at 370 μmol·mol-1 (CO2) and 450±20 μmol·m-2·s-1 PAR. The cultivars responded similarly to increasing temperature and did not differ in most photosynthetic parameters except gs. The PN increased between 20 and 30 °C, thereafter increasing only slightly to 35 °C. On average, increasing temperature from 20 to 30 °C increased PN by 69%. Carboxylation efficiencies (Ca/Ci ratio) ranged from 1.12–2.33 mmol·mol-1 while maximum PN were 3.25, 3.90, 5.49, 4.19 μmol·m-2·s-1 for Carson, RCC, Cascade, and Oranza, respectively. The E did not reach maximum at 35 °C while gs peaked at 30 °C and then decreased by 93% at 35 °C. The water use efficiency (WUE) decreased with an increase in temperature due to increases in both PN and E. The results indicate that increasing temperatures above the seasonal average (<20 °C) increases both PN and E up to 30–35 °C. An increase in photosynthesis due to an increase in temperature is expected to hasten growth. Carrots may be able to withstand a moderate increase in temperature.