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Hussein Al-Amier, Robert Lussier, Ming Coler, Margaret Stoltzman, and Lyle Craker

The stress level in a plant may be directly associated with the intensity of the Kautsky effect (the sudden increase in fluorescence emission by chlorophyll following a dark adaptation). The decrease in photosynthetic efficiency, linked with the rate of photochemistry of plants under stress, provides a definitive signature (graphical pattern) that can be quantified and monitored, even for plants that have no visible stress symptoms. Using a prototype GrowScanner®, signature differences in plants under nitrogen and water stress, as compared with plants not under stress, could be detected and measured. Returning stressed plants to a nonstressed condition returned the stress signatures to that of control plants not under stress. Development of the technology may provide a relatively quick, presymptomatic methodology for detecting plant stress without sacrificing plant tissue.

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James A. Hardin, Michael W. Smith, Paul R. Weckler, and Becky S. Cheary

precision agriculture practices in pecan production. Much of the N in a leaf is partitioned in chlorophyll; thus, a sensor that measures chlorophyll can often be used to quantify the amount of N in a leaf ( Filella et al., 1995 ). The basis for most optical

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Jianjun Li, Xiaoya Lian, Chenglin Ye, and Lan Wang

the plant material. A spectrophotometer was used to determine chlorophyll a, chlorophyll b, and carotenoid content according to the wavelengths of their maximum absorption peaks, which were 665, 649, and 470 nm, respectively. Determination of the three

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Jinhong Yuan, Man Xu, Wei Duan, Peige Fan, and Shaohua Li

about how P n is limited and whether there are changes in energy fluxes in the photosynthetic apparatus. The status of the photosynthetic apparatus may be investigated in vivo using fast chlorophyll a fluorescence transient analysis ( Strasser and

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Charalambos I. Siminis and Manolis N. Stavrakakis

Iron (Fe) is an essential nutrient for plants, which catalyzes crucial cellular functions such as chlorophyll synthesis, chloroplast development, and antioxidative cell protection ( Marschner, 1995 ). Despite being abundant in soils, Fe mainly

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Robert E. Rouse, Sandra P. Perez, and Sally B. Davenport

The Minolta chlorophyll meter SPAD-502 (Minolta Camera Company, 101 Williams Drive, NJ 07446, USA) was evaluated as an accurate, nondestructive means to measure chlorophyll content in citrus leaves. Meter readings from leaves of sweet orange and grapefruit citrus cultivars were used to develop a standard curve for citrus. A significant correlation value of 0.96 was calculated between the chlorophyll meter readings and actual chlorophyll extraction levels. The development of a standard curve using the SPAD-502 chlorophyll meter had not been established on citrus. The SPAD-502 chlorophyll meter proved to be a quick, accurate, simple, and nondestructive way to determine chlorophyll content in citrus leaves.

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Lingyan Chen, Jinli Lai, Tianyou He, Jundong Rong, Muhammad Waqqas Khan Tarin, and Yushan Zheng

variegated leaves provide suitable materials for studying the mechanism of chlorophyll biosynthesis and biodegradation, the chloroplast structure, and the photosynthetic process. The biosynthesis of chlorophyll is a complex process, which involves chemical

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Burcu Begüm Kenanoglu, Ibrahim Demir, and Henk Jalink

variation in seed maturity results in variation in plant growth and development. Therefore, separating out less mature seeds would enhance the overall quality of a seed lot. Chlorophyll content of the seedcoat in many species decreases as seed matures

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Robert K. Prange, John M. DeLong, Peter A. Harrison, Jerry C. Leyte, and Scott D. McLean

A new chlorophyll fluorescence (F) sensor system called FIRM (fluorescence interactive response monitor) was developed that measures F at low irradiance. This system can produce a theoretical estimate of Fo at zero irradiance for which we have coined a new fluorescence term, Fα. The ability of Fα to detect fruit and vegetable low-O2 stress was tested in short-term (4-day) studies on chlorophyll-containing fruit [apple (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.), pear (Pyrus communis L.), banana (Musa ×paradisiaca L.), kiwifruit (Actinidia deliciosa C.S. Liang & A.R. Ferguson), mango (Mangifera indica L.), and avocado (Persea americana Mill.)] and vegetables (cabbage (Brassica oleracea L. Capitata Group), green pepper (Capsicum annuum L. Grossum Group), iceberg and romaine lettuce (Lactuca sativa L.)). In all of these fruit and vegetables, Fα was able to indicate the presence of low-O2 stress. As the O2 concentration dropped below threshold values of 0 to 1.4 kPa, depending on the product, the Fα value immediately and dramatically increased. At the end of the short-term study, O2 was increased above the threshold level, whereupon Fα returned to approximately prestressed values. A 9-month study was undertaken with `Summerland McIntosh' apple fruit to determine if storing the fruit at 0.9 kPa O2, the estimated low O2 threshold value determined from Fα, would benefit or damage fruit quality, compared with threshold + 0.3 kPa (1.2 kPa O2) and the lowest recommended CA (1.5 kPa O2). After 9 months, the threshold treatment (0.9 kPa) had the highest firmness, lowest concentration of fermentation volatiles (ethanol, acetaldehyde, ethyl acetate) and lowest total disorders. Sensory rating for off-flavor, flavor and preference indicated no discernible differences among the three treatments.

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Dean A. Kopsell, Carl E. Sams, Dennis E. Deyton, Kristin R. Abney, David E. Kopsell, and Larry Robertson

chlorophylls as valuable phytochemicals ( Ferruzzi and Blakeslee, 2007 ). Recent evidence is also suggesting that dietary chlorophylls may possess biological activities associated with cancer prevention, antimutagenic activity, and induction of apoptosis in