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Michele R. Warmund, Bruce H. Barritt, John M. Brown, Karen L. Schaffer and Byoung R. Jeong

Abbreviation: MRI, magnetic resonance imaging. Contribution from the Missouri Agr. Expt. Sta. J. Ser. no. 11,590. We gratefully acknowledge Steve B. Pickup, Dept. of Radiology, Univ. of Missouri Hospital and Clinics, for his assistance. The cost of

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Lisa J. Rowland, Dehua Liu, Merle M. Millard and Michael J. Line

Dormant and chilled highbush blueberry (Vaccinium corymbosum L.) flower buds were examined by magnetic resonance imaging (MRI). T2 relaxation times of water molecules were too short to create images from flowers within buds that were dormant and had received no chilling, but they were sufficiently long to create images from buds that had their chilling requirement satisfied. To explain the change in relaxation times, we concluded that water is present in a motionally restricted form in flowers of dormant blueberry buds and in a freer form in flowers of buds after the chilling requirement has been satisfied. T2 values for chilled blueberry buds indicated that one population of water molecules with a detectable T2 time was present in flowers of chilled buds with a relaxation time of ≈8 to 15 ms.

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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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Christopher J. Clark, Annette C. Richardson and Ken B. Marsh

Whole-fruit proton magnetic resonance (MR) imaging was performed on satsuma mandarin (Citrus unshiu Markovich cv. Miho Wase) during a 15-week period commencing 10 weeks after anthesis and continuing to maturity, and at 6 weeks after anthesis the following season. Images with long repetition times (>1600 ms) and short echo times (20 ms) provided the clearest details of anatomical changes in the peel (flavedo, albedo) and vascular system, while those with similar repetition times but longer echo times (120 ms) were best for viewing juice sac morphology within pulp segments. At 6 weeks after anthesis, images of fruits of slightly different physiological ages highlighted rapid changes in the vascular bundles and albedo tissue at this stage of development. Variation in the relaxation measurements, T1 and T2, was determined from quantitative MR images of the juice sacs in equatorial slices, and images of expressed juice from whole fruit. Seasonal measurements of T1 determined in situ (1760 ms) were significantly greater than those in juice (1413 ms). By contrast, there was no mean seasonal difference between in situ T2 measurements (360 ms) and those for juice (332 ms). No associations between trends in the MR data and total soluble solids, pH, titratable acidity, and sugar and organic acid composition of the juice were established. Cell structure is identified as a hindrance in the use of quantitative MR imaging for probing compositional changes in solution in serial imaging studies.

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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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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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B.L. Tan, N. Reddy, V. Sarafis, G.A.C. Beattie and R. Spooner-Hart

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) were used to detect petroleum-derived spray oils (PDSOs) in citrus seedlings and trees. The NMR spectrum of the phantom containing 10% (v/v) of a nC24 agricultural mineral oil (AMO) showed the resonance of the water protons at δ ≈ 5 ppm, while the resonance of the oil protons at δ = 1.3 to 1.7 ppm. The peak resolution and the chemical shift difference of more than 3.3 ppm between water and oil protons effectively differentiated water and the oil. Chemical shift selective imaging (CSSI) was performed to localize the AMO within the stems of Citrus trifoliata L. seedlings after the application of a 4% (v/v) spray. The chemical shift selective images of the oil were acquired by excitation at δ = 1.5 ppm by averaging over 400 transients in each phase-encoding step. Oil was mainly detected in the outer cortex of stems within 10 d of spray application; some oil was also observed in the inner vascular bundle and pith of the stems at this point. CSSI was also applied to investigate the persistence of oil deposits in sprayed mature Washington navel orange (Citrus ×aurantium L.) trees in an orchard. The trees were treated with either fourteen 0.25%, fourteen 0.5%, four 1.75%, or single 7% sprays of a nC23 horticultural mineral oil (HMO) 12 to 16 months before examination of plant tissues by CSSI, and were still showing symptoms of chronic phytotoxicity largely manifested as reduced yield. The oil deposits were detected in stems of sprayed flushes and unsprayed flushes produced 4 to 5 months after the last spray was applied, suggesting a potential movement of the oil via phloem and a correlation of the persistence of oil deposit in plants and the phytotoxicity. The results demonstrate that MRI is an effective method to probe the uptake and localization of PDSOs and other xenobiotics in vivo in plants noninvasively and nondestructively.

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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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Dehua Liu, Miklos Faust, Merle M. Millard, Michael J. Line and Gary W. Stutte

Magnetic resonance imaging was used to determine water states in paradormant apple (Malus domestica Borkh.) buds and during early events when buds resumed growth. Proton density and states of water were determined by creating image maps of proton density and relaxation times (T2). Summer-dormant (paradormant) buds had T2 relaxation times up to 30 ms. This water in bud tissues is considered relatively free compared to water that had T2 relaxation times of <1 ms in other parts of the stem and bark. Buds were forced to grow either by pruning off the terminal bud or by starting the bud with thidiazuron (TDZ). Both treatments gave essentially the same results. After treatment, buds started to grow immediately and water moved into the stem and into the bud. As there was more free water in the bud, T2 values ranged up to 50 ms. There appeared to be an inhibitory gradient down on the shoot, which was removed temporarily by excising the top bud. However, between the 2nd and 10th day after removal of the top bud this dominance was reinstated by the highest bud on the stem, which eventually formed a shoot. TDZ treatment overcame this inhibitory gradient effect. There was also a growth potential gradient coinciding with the inhibitory gradient. The growth of lower buds was much slower than that of the upper buds. The growth potential gradient was not overcome by TDZ treatments.

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Merle M. Millard, Dehua Liu, Michael J. Line and Miklos Faust

Magnetic resonance imaging estimates unreasonably high T2 times when creating T2 images in woody plants when tissues contain a limited amount of water. We developed a system to correct such images. Tissue distribution of proton density and states of water were determined by creating images of proton density and T2 relaxation times in summerdormant (paradormant) apple (Malus domestica Borkh.) buds. These images reveal that the proton density and water states obviously are not distributed uniformly in the bud and stem; but, the distribution of water depends greatly on the tissue type (bark, xylem, or meristem of the stem), and there are differences in the states of water even within the same tissue. At low proton density T2, calculated relaxation times were unreasonably high in tissues, with the exception of meristem of the shoot. In buds that were induced to grow and in which proton density was higher, T2 times appeared as expected. Variance of T2 times in tissues containing little water was 50 times higher than in those with a higher water content. Data with such high variance were excluded from the images; thus, the image was “corrected.” Corrected images of T2 times fit the distribution of water indicated by the proton density images well.