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John L. Maas and M.J. Line

We report the use of nuclear magnetic resonance (NMR) imaging to detect differences in invasion and colonization of fruit by pathogens (Botrytis cinerea, Colletotrichum acutatum, and Phytophthora cactorum), and bruise wounds are sharply distinguishable from healthy fruit tissue by their T1 times. Digitized images from T1 images clearly show two or more zones of pathogen activity in fruit tissue. The innermost zone corresponds to the area of greatest invasive activity at the leading margin of the infection. A second zone corresponds to the area of tissue that has been killed and is being degraded by the pathogen. Sometimes, a third zone is present at the outer border of the lesion and this correspond to where aerial sporulation may occur. Images of bruises, however, are uniform with no apparent gradations in T1 characteristics. Detection of fruit deterioration and decay is important in understanding and controlling postharvest loss of fruit crops. The nondestructive nature of MRI provides a means to quantify the process of decay development and control measures applied to fruits.

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John L. Maas and Michael J. Line

Nuclear magnetic resonance (NMR) can be used to examine tissue structure and developmental changes during growth and maturation of plant organs nondestructively. Spin-lattice, relaxation time (T1)-weighted, inversion recovery, spin-echo images of strawberry (Fragaria×ananassa Duch.) flower buds were acquired at 3 and 1 day before anthesis and receptacles at 4, 10, 15, and 25 days after anthesis (DAA). The central pith and ovules of flower buds imaged intensely with inversion echo times between 0.1 and 0.5 seconds. Achenes and the vascular cylinder, composed of vascular bundles surrounding the pith, were prominent in receptacles at 4 and 10 DAA. Vascular bundles leading to achene positions, cortex and pith tissues, and the vascular cylinder were evident in receptacles at all developmental stages. A general trend to homogeneity of structure was observed in images of receptacles nearing full maturity (25 DAA). Inversion recovery, spin-echo NMR microimaging may be useful for studying internal physicochemical changes in flower buds and fruit of strawberry and of other fruit crops.

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M.S. Roh, M. Line, Y.H. Joung, and P. Brannigan

Ornithogalum hybrid bulbs (selection 327-2) were stored dry at 10, 16, 22, 28, and 35 °C for 6 weeks upon harvest. After storage, bulbs were subjected to a nuclear magnetic resonance (NMR) imaging to obtain the longitudinal spin-lattice relaxation time (T1) profile across the cross section of intact bulbs and to a scanning electron microscopy (SEM) to observe an inflorescence development. Bulbs were forced in a greenhouse maintained at 21/19 °C. When bulbs were stored at 10, T1 was shorter through the cross section of bulbs and the shoot apex was under a vegetative stage. This suggests that dormancy was not broken during the storage, leaf emergence was delayed, and plants failed to flower. Bulbs stored at 22 and 28 °C formed the primary scape and inflorescence with several florets. At the base of the primary scape of bulbs stored at 22 °C, a vegetative apex was observed by both MR imaging (MRI) and SEM. In the center of bulbs where leaves and floral organs were present, T1 was longer as compared to the scales. This suggests that dormancy in the scales was broken and the leaves and scape were ready to emerge. Leaf emergence and flowering was the fastest when bulbs were stored at 22 °C and at 16 or 22 °C, respectively. Due to its nondestructive nature, MRI can be used to study the state of bulb dormancy and also the progress of inflorescence development during bulb storage prior to planting.

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P.C. Wang, C.Y. Wang, H.F. Song, and Z.J. Yan

Potatoes with hollow heart or brown center are considered to be of poor quality for both fresh and processing markets. A reliable nondestructive method, which can distinguish affected and normal potatoes, is described here. A Varian 4.7 Tesla, 33-cm horizontal-bore spectroscopy/imaging system was used to obtain nuclear magnetic resonance (NMR) images of potatoes. A two-dimensional multi-slice spin-echo imaging technique was used to acquire the cross-sectional images along the longitudinal direction. The echo time was 35 msec and the repetition time was 1.2 sec. A total of 13 slice images were taken for each potato. A one-dimensional projection technique was also performed to evaluate the possibility of using fast-scan method. The brown center showed high intensity in long echo scans due to its longer TL relaxation time. A suberin-like layer resembling the periderm developed on the cavity wall of hollow heart causing a tan or dark brown coloration. This cavity wall also appeared in high intensity on the image. The affected potatoes can easily be sorted out using this nondestructive NMR imaging technique.

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Vincent M. Russo and John Wright

Understanding carbon metabolism can provide insight into physiological processes regulating yield, senescence, and resistance to pathogens in sweet corn (Zea mays L.). This study was conducted to determine if nuclear magnetic resonance (NMR) spectroscopy could be used to monitor changes in carbon metabolism at various growth stages in the shrunken-2 sweet corn cultivar Illini Gold. The 7th, 9th, and 11th stalk internodes were excised at midwhorl (V9), tassel emergence, 50% silking, and fresh-market harvest stages. The rind was removed and the sap expressed. Carbon-NMR spectroscopy was conducted with a 200.7 MHz machine on the expressed sap. From V9 through 50% silking, peaks in spectra were uniformly grouped from ≈61 to ≈104 ppm. At fresh-market stage, additional peaks were found in the spectra at ≈17 to ≈20 ppm, with the majority of peaks found from ≈57 to ≈104 ppm. The biological importance of these changes in carbon metabolism in sweet corn are not clear. Efforts are under way to identify the carbon-based compounds associated with the peaks.

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Carmen del Río and Ana M Romero

Several experiments showed that whole, unmilled olives (Olea europaea L.) could be dehydrated in 42 hours in a forced-air oven at 105 °C (221 °F), so that they could be used in determining their oil content in a nuclear magnetic resonance (NMR) analyzer. After confirming that the NMR and the official Soxhlet methods estimate the same oil percentages in milled olives, linear regression analysis also showed that NMR provides the same oil percentage results with milled and unmilled fruit. This new method avoids sample manipulation before dehydrating the fruit, making it possible to work with olive samples weighing as little as 70 g (2.47 oz). It allows for processing a large number of samples in a short period of time and may be also used with unmilled fruit flesh. The method is also very useful for screening genotypes, either from germplasm banks or progenies from olive breeding programs, and for evaluating cultivars in comparative trials.

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Anne Fennell, M.J. Line, and M. Faust

Changes in water status have been associated with various stages of dormancy and freezing tolerance in woody perennials. Recent studies in apple indicate that changes in the state (bound vs. free) of bud water are strongly correlated with the end of dormancy. In this study nuclear magnetic resonance imaging (NMRI) was used to monitor changes in the state of bud water during the photoperiodic induction of endo-dormancy in Vitis riparia. Bud water status was monitored using proton relaxation times from T1 and T2 images determined at 2, 4, and 6 weeks of long (LD) or short (SD) photoperiod treatments. Bud dormancy was determined by monitoring budbreak in plants defoliated after photoperiod treatments. NMRI allowed nondestructive monitoring of changes in tissue water state. T1 and T2 maps indicated changes in the state of the water in bud and stem tissues during the 6 weeks of treatment. Differences in relaxation times for nondormant and dormancy-induced (reversible) buds were not clear. However, T2 relaxation times were lower in the dormant buds than in the nondormant buds.

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M.E. Saltveit

Tomato fruit undergo an orderly series of physiological and morphological changes as they progress from mature-green (MG) to red-ripe. Fruit are commercially harvested at the MG stage, a stage which often encompasses fruit of varying degrees of maturity. The ability to predict the time required for MG fruit to ripen would reduce variability in experiments and could be commercially used to pack fruit that would ripen uniformly. Nuclear magnetic resonance (NMR) imaging can nondestructively measure internal changes associated with plant growth and developmental. In this study, NMR images were taken of freshly harvested tomato fruit (Lycopersicum esculentum cv. Castlemart) at different stages of maturity and ripeness. Measurements were also made of the stage of ripeness, rate of respiration and ethylene production, lycopene and chlorophyll content, density of the pericarp wall, and condition of locular tissue. NMR images showed substantial charges in the pericarp wall and locular tissue during maturation and ripening of tomato fruit. However, it was difficult to objectively evaluate these visual changes with other ripening parameters. For example, increased lightness and graininess of the pericarp wall image was associated with a decrease in wall density; while lightening of the locular image was associated with tissue liquefacation. Use of NMR imaging in studies of tomato fruit ripening will be discussed.

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Anne Fennell and Michael J. Line

Physiological and biophysical changes were monitored during shoot maturation and bud endodormancy induction in grape (Vitis riparia Michx.) under controlled environments. Growth, dry weight (DW), periderm development, bud endodormancy, and nuclear magnetic resonance imaging (MRI) T2 relaxation times were monitored at 2, 4, or 6 weeks of long-photoperiod [long day (LD), 15 h, endodormancy inhibition] or short-photoperiod [short day (SD), 8 h, endodormancy induction] treatments at 15/9 h day/night thermoperiod of 25/20 ± 3 °C. Shoots on LD plants grew throughout the entire study period, although the rate of growth decreased slightly during the 6th week. Shoot growth slowed significantly after 2 weeks of SD, was minimal by the 4th week of SD and most of the shoot tip meristems had abscised after 6 weeks of SD. Endodormancy was induced after 4 weeks of SD. DW of the stem and buds increased with increasing duration of LD and SD. While bud DW increased more under SD than LD, stem DW increased more under LD than SD. T2 relaxation times were calculated from images of transverse sections of the grape node. There was a slight decrease in the T2 times in the node tissues with increased duration of LD treatment, whereas SD induced a significant decrease in T2 times during endodormancy induction. T2 values for the node decreased after 4 weeks of SD, coinciding with endodormancy induction. Separation of node tissues into bud, leaf gap, and the remainder of the stem and analysis of the proportion of short and long T2 times within those tissues indicated differential tissue response. A greater proportion of short T2 times were observed in the 2-week SD leaf gap tissue than in the LD and the proportion of short T2 times continued to increase with subsequent SD treatment. Bud and all other stem tissues had a greater proportion of short T2 times after 4 weeks of SD, coinciding with bud endodormancy induction. The proportion of short and long T2 times in a tissue was a better indicator of endodormancy than the averaged T2 time for the tissue. Thus, MRI allows nondestructive identification of differential tissue response to photoperiod treatments and makes it possible to separate normal vegetative maturation responses from endodormancy induction.

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Toshihiko Sugiura, Mitsura Yoshida, Jun Magoshi, and Sukeyuki Ono

Physiological changes in `Hakuho' peach [Prunus persica (L.) Hatsch] flower buds during endodormancy and ecodormancy were investigated based on their water status measured by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy. The developmental stage in ecodormancy, which was estimated as the number of days between the sampling date for shoots and the bloom date after forcing, was dominated by absorption of water and was closely related to the water content per dry weight. Two types of water differing in spin-lattice relaxation time (T1) of protons were detected in the flower buds. Water with the shorter T1 was considered to be freezing water as well as that with a longer T1. Nonfreezing water can not be detected by NMR. The change in the longer T1 coincided with the change in the water percentage relative to bud fresh weight and reflected the physiological development in ecodormancy. The shorter T1 value started to increase shortly before rest break and may have some relation with the physiological change at rest break.