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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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all photons absorbed by chlorophyll and accessory pigments are used to drive the light reactions. Excess absorbed photons can cause damage within the chloroplast. The reaction center of PSII, particularly the D1 protein, is highly susceptible to light

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dissipated as heat and a small fraction is re-emitted as chlorophyll fluorescence ( Maxwell and Johnson, 2000 ). The quantum yield of photosystem II, the efficiency with which photosystem II (PSII) uses absorbed photons for electron transport, or the moles of

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-adapted plant Alocasia macrorrhizos (giant taro). Meanwhile, when both species are grown in shade, giant taro allocates more nitrogen proportionally toward chlorophyll development to increase light interception (thus increasing photosynthetic activity at low

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). Photosynthesis of orange ( Citrus sinensis ) and lemon ( Citrus limon ) fruit, which takes place in the chlorophyll-containing flavedo, was initially considered of minor importance in fruit development and only compensating for respiration, even at maximum

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reflectance sensors. Our results support the idea of developing remote sensing sensors with specific bands (such as those for chlorophyll content, normalized difference vegetation index) that capture the moisture status of pecan orchards precisely and early

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, Eindhoven, The Netherlands) and incandescent lights (A15 FR 130V 3M 25W; Halco Lighting Technologies, Norcross, GA) provided 443 ± 17 μmol·m −2 ·s –1 from 0600 to 2200 hr throughout propagation. Light was measured with a quantum light sensor (SQ-222

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overall reduction in growth but no obvious signs of visible damage ( Wellburn, 1990 ) and mainly affect the physiological metabolism of plants. Chlorophyll (Chl) is the most important plant pigment because it has a crucial role in photosynthesis ( Croft et

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·s −1 and resulted in a DLI of 7.5 mol·m −2 ·d −1 . The RH inside the gas exchange chambers was measured using a temperature and humidity sensor (HTO-45R; Rotronic Instruments, Crawley, UK). In general, RH inside gas exchange chambers depended on the

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received phosphorus and potassium at rates of 17.9 and 12.8 g·m −2 , respectively, and they were supplied with irrigation water. Measurements and methods. Soil water content was measured using a portable capacitance sensor system (Diviner 2000; Sentek

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