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Lailiang Cheng and Leslie H. Fuchigami

Based on the curvilinear relationship between carboxylation efficiency and leaf N in apple leaves, we hypothesized that deactivation of Rubisco accounts for the lack of response of photosynthesis to increasing leaf N under high N supply. A wide range of leaf N content (from 1.0 to 5.0 g·m–2) was achieved by fertigating bench-grafted Fuji/M26 apple trees for 6 weeks with different N concentrations using a modified Hoagland solution. Analysis of photosynthesis in response to intercellular CO2 under both 21% and 2% O2 indicated that photosynthesis at ambient CO2 was mainly determined by the activity of Rubisco. Measurements of Rubisco activity revealed that initial Rubisco activity increased with leaf N up to 3.0 g·m–2, then leveled off with further rise in leaf N, whereas total Rubisco activity increased linearly with increasing leaf N throughout the leaf N range. As a result, Rubisco activation state decreased with increasing leaf N. Photosynthesis at ambient CO2 and carboxylation efficiency were both linearly correlated with initial Rubisco activity, but showed curvilinear relationships with total Rubisco activity and leaf N. As leaf N increased, photosynthetic nitrogen use efficiency declined with decreasing Rubisco activation state.

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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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Milton E. McGiffen Jr., John B. Masiunas, and Morris G. Huck

Eastern black nightshade (Solanum ptycanthum) and black (Solanum nigrum) nightshade are difficult to control in tomato, interfering with harvest and decreasing fruit quality and yield. In irrigated tomatoes, soil water depletion was greater as nightshade density increased. However, tomato yield loss due to black nightshade was greatest at the lower weed densities. As density increases, photosynthetic activity (photosynthetic rates, stomatal conductance, intercellular CO2 concentration, and stomatal resistance) of black nightshade is more affected than eastern black nightshade. Photosynthetic activity of tomato is the least affected. In greenhouse experiments where water was denied for approximately a week prior to measurement, tomatoes were more sensitive to water stress than were nightshades. Nightshades were more adapted to drought stress than were tomatoes.

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J.S. Seron, R.J. Ferree, S.L. Knight, M.A.L. Smith, and L.A. Spomer

Tolerance of increased salinity by tomato is of great importance to the tomato processing industry, where increased conductivity of up to 6 dS m-1 is used to increase specific yield components. A new line of miniature dwarf tomato, Lycopersicon esculentum Mill. cv. Micro Tom, was evaluated for photosynthetic response to elevated salinity. Tomatoes were grown in solution batch culture and subjected to constant salt treatments of 2.4 (control), 7.6, 12.8, or 18 dS m-1. Weekly photosynthetic measurements were made beginning week 4 on the most recent fully open leaf or leaf opposite a fruit. Net photosynthesis decreased across all salt treatments over the last six weeks of sampling. As salinity level increased, net photosynthesis decreased compared to the control. The 18 dS m-1 treatment reduced net photosynthesis relative to 12.8 and 7.6 dS m-1. Although salinity increased succulence, limitations to net photosynthesis were due to diminished utilization of intercellular CO2, rather than reduced internal CO2 concentration or stomatal conductance.

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Qibing Wang and Jianjun Chen*

Ficus benjamina is considered to have a high degree of morphological and physiological plasticity in response to light levels. In this study, leaf area and thickness, specific leaf area (SLA), chlorophyll content, and photosynthetic characteristics of Ficus benjamina `Common'; grown in a shaded greenhouse under four maximum photosynthetic photon flux densities (PPFDs) of 150, 250, 450, or 650 μmol·m-2·s-1 were investigated. Results showed that plants grown under 450 and 650 PPFDs had higher SLA and leaf thickness but smaller leaf areas than those grown under 150 and 250 PPFDs. Total chlorophyll content per unit leaf area decreased as PPFDs increased. Net photosynthetic rates (Pn) increased from 2.7 μmol·m-2·s-1 under 150 PPFD to 5.7 μmol·m-2·s-1 under 450 PPFD, then slightly decreased to 5.5 μmol·m-2·s-1 under 650 PPFD. The highest net photosynthetic rate was not associated with higher intercellular CO2 concentrations (Ci) and stomatal conductance (gs) as plants grown under 250 PPFD had the highest (Ci) (259 ppm) and gs (0.1 mol·m-2·s-1), which suggests that photosynthetic enzymes could play a increasing role under 450 PPFD. Plant quality, however, was not necessarily correlated with the Pn because only those grown under 250 PPFD had appropriate heights, large and dark green leaves, and well-spread branches, and thus were graded higher than plants grown under the other PPFDs. This study shows that fine-tuning production light level is important for high quality Ficus benjamina production.

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Li-Song Chen, Brandon R. Smith, and Lailiang Cheng

1 Current address: Department of Horticulture, Fujian Agriculture and Forestry University, Fuzhou 350002, P.R. China. 2 To whom reprint requests should be addressed: fax: +1-607-255-0599; e-mail: LC89@Cornell.edu This work was supported in part by

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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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Israel Weiss, Yosef Mizrahi, and Eran Raveh

Most studies on the physiological responses of plants to increasing CO 2 concentrations have focused on C 3 and C 4 photosynthetic pathway plants. It has been found that CO 2 enrichment enhances net CO 2 uptake and growth of C 3 plants by 30

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Sorkel Kadir, Gaganpreet Sidhu, and Kassim Al-Khatib

1 To whom reprint requests should be addressed; e-mail skadir@ksu.edu . 2 Professor, Agronomy Department. With our appreciation, funding for this study was provided by the Initiative for Future Agricultural Food System, U.S. Department of

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Lloyd L. Nackley, Jig Han Jeong, Lorence R. Oki, and Soo-Hyung Kim

apparent photosynthetic downregulations especially at low intercellular CO 2 concentrations in mid- and high-N. The values were more variable when N supply was low ( Fig. 5 ). Together with a lower V cmax , this result suggests that biochemical