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Rui Zhou, Lailiang Cheng and Abhaya Dandekar

Considering starch synthesis was enhanced in leaves of transgenic apple trees with decreased sorbitol synthesis, we hypothesized that starch degradation must be up-regulated correspondingly to maintain carbon supply to sink tissues. Compared with the untransformed control, mature leaves of the transgenic plants had a larger drop in starch concentration between dusk and pre-dawn, higher maltose concentration, and higher activities of two key enzymes in starch degradation: -amylase and cytosolic glucosyltransferase during the day and night. 14C-maltose and 14C-glucose were fed to the apple leaves to study the fate of starch breakdown products in the synthesis of sorbitol and sucrose. Under light, a larger proportion of both 14C-maltose and 14C-glucose were converted to sorbitol than to sucrose in the untransformed control, whereas conversion of 14C-maltose and 14C-glucose to sucrose predominated over that to sorbitol in the transgenic apple leaves. The leaf samples fed with 14C-maltose and 14C-glucose in the dark are still being analyzed, but it appears that sucrose is the main product in both the untransformed control and the transgenic plants. These results support the hypothesis that starch degradation is up-regulated in the transgenic plants.

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Stephen F. Klauer, Chuhe Chen, Paul W. Foote and J. Scott Cameron

On four dates during the 1991 growing season, gas exchange rates were measured on the same middle leaflets every 3 h from 7am-10pm from deflowered (DF) and fruiting (F) red raspberry (Rubus idaeus L. cv. “Meeker”) canes. Concurrently, the adjacent side leaflets were sampled for anatomical starch determination. The dates corresponded to the late anthesis/early green fruit, early red fruit, late red fruit, and post fruit maturity stages of the growing season. For all dates, CO2 assimilation (A) was highest from 7-10am, lowest at 4pm, and increased at 7pm. Overall A peaked during fruit development. Leaves of F canes had greater A than leaves of DF canes during fruit development, but rates were similar after fruit maturity.

Starch accumulation in leaf cross-sections generally followed the diurnal pattern observed for A. Starch appeared heaviest from 7am-lpm and often showed an increase from 7-10pm. Leaves from DF canes generally had a greater accumulation of starch. Seasonally, leaf starch from F canes appeared greatest at late anthesis, decreased during fruit development and was very low post fruit maturity. Leaf starch in DF canes appeared greatest at the late anthesis and late red fruit stages.

DF leaves had greater dry weight accumulation than F leaves during the red fruit stages. A Western blot showed that Rubisco levels as a percentage of total soluble protein were higher during fruit development and decreased after fruit maturity.

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Bing Liu, Hong Zhou, Sha Cao, Yi-ping Xia and Rajeev Arora

carbohydrates (total soluble sugars and starch) to explore any correlations between the changes in these carbohydrates and deacclimation kinetics. Materials and Methods Plant material and sampling environment. The experiment was conducted using 2-year

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Juan L. Silva and Kednal Alexis

Models for prediction of starch, alcohol-insoluble solids (AIS) and glucose were developed by measuring the viscosity of freeze-dried sweetpotato [Ipomoea batatas (L.) Lam] flour. Green (processed within 24 h) and cured. Jewel and Beauregard roots-were cooked, peeled, pureed and freeze-dried. Viscosity of the flour was measured with a Brabender Viscoamylograph and a Brookfield Viscosimeter. Total solids, starch, AIS, glucose, fructose and sucrose were quantified. There was a strong correlation (R2=0.99) between Brookfield and Brabender viscosity. Results showed significant correlations between Brookfield apparent viscosity or Brabender viscosity units at the gelatinization stage and starch (R2=0.82 and 0.81), AIS (R2=0.S7 and 0.81), and glucose (R2=0.87 and 0.86) content. Apparent viscosity of flour from green roots increased through gelatinization and upon cooling, but that from cured roots remained constant throughout.

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Kenji Katayama, Katsumi Komaki and Seiji Tamiya

Near infrared analysis was used to predict the starch, moisture, and sugar content in sliced fresh sweetpotato [Ipomoea batatas (L.) Lam.] storage roots. Samples were collected in each of three growing years. The best calibration equation for starch from combined samples (1989 to 1991) showed a multiple correlation coefficient (R) of 0.949, a standard error of calibration (sec) of 2.01, and a standard error of prediction (sep) of 1.91. The R, sec, and sep for moisture and sugar were 0.930, 1.85, and 2.00, and 0.837, 1.30, and 1.21, respectively. Calibrations based on samples from a given year adequately predicted the variables but could not account for variances introduced by samples from other years. Multiyear calibrations based on several years of data adequately predicted starch and moisture content in root slices. Thus, multiyear calibrations with annual bias adjustments can be applied to screening sweetpotato breeding germplasm for these two variables.

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Marina Petreikov, Lena Yeselson, Shmuel Shen, Ilan Levin, Arthur A. Schaffer, Ari Efrati and Moshe Bar

( Schaffer et al., 2000 ). The rationale behind this strategy lies in the observation that the developing tomato fruit is a transient starch accumulator and the starch in the immature fruit may serve as a reservoir for soluble sugar accumulation during

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Teresa A. Morrison, Russell Pressey and Stanley J. Kays

Staple-type lines of sweetpotato [Ipomoea batatus (L.) Lam.] do not sweeten significantly upon cooking as compared to the traditional-type lines. Four lines exhibiting distinct differences in sweetness after cooking were evaluated for changes in α- and ß-amylase activity and reducing sugars (by HPLC) at harvest, after curing, and at intervals during 180 days of storage. The traditional cultivar `Jewel' and staple-type line `Sumor' displayed high a- and ß-amylase activities, which rose from low levels at harvest to peak levels ≈ 90 days into the storage period. Staple-type lines `99' and `86' displayed significantly lower a- and ß-amylase activities. By using polyclonal sweetpotato ß-amylase antibody and western blot following native- and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it was confirmed that a lower level of ß-amylase synthesis existed in `99' and `86'. Quantitatively, `Jewel', `Sumor', and an additional staple-type line, `HiDry', had 361,374, and 365 μg ß-amylase protein per gram of fresh storage root tissue, respectively, while `99' and `86' possessed <60 and 12 μg·g-1, respectively. In raw roots, individual (glucose, fructose, and sucrose) and total sugar concentrations were significantly higher in `Jewel' than in `Sumor', `99', or `86'. Only trace amounts of maltose were found in raw roots of any line. Sucrose, glucose, and fructose concentrations decreased with baking in all lines except `86', in which they increased. There was substantial maltose produced by baking `Jewel' and `Sumor', but only trace amounts found in baked `99' and `86'. Sweetpotato germplasm can be separated into four general classes based on initial sugar concentration and changes during cooking: 1) low sugars/low starch hydrolysis, 2) low sugars/high starch hydrolysis, 3) high sugars/low starch hydrolysis, and 4) high sugars/high starch hydrolysis. At least two mechanisms may confer the lack of starch hydrolysis and subsequent sweetening in staple-type sweetpotato: 1) inhibition of ß-amylase synthesis, and 2) a nonenzyme mediated mechanism.

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S.J. Li, T.J. Facteau and P. Chen

Several characteristics of amylases involved in starch degradation were studied in extracts from immature (30 days before harvest) `d'Anjou' pears (Pyrus communis L.). Enzyme activity was not detected until after at least 60 minutes of incubation in frozen or lyophilized tissues. Activity increased significantly after 90 minutes and increased linearly after 2 to 12 hours of incubation. Activity was greater, however, in frozen than in lyophilized tissues. Three buffers (acetate, tris-HCl, and imidazole-HCl) were used at a range of pH levels (4.6-8.2) to ascertain the optimum assay system. Highest specific activity was recorded with acetate buffer at pH 5.6. The Km value in this system was 1.43 × 10-3g·ml-1. Specific activity increased as Ca concentration in the reaction mixture increased from 1 to 15 mm CaCl2 but did not change as Ca concentration increased from 15 to 25 mm CaCl2. The `d'Anjou' pear amylases were purified 5.7-fold using ammonium sulfate fractionation.

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Tekalign Tsegaw, S. Hammes and J. Robbertse

Potato (Solanum tuberosum L.) treatment with paclobutrazol resulted in short and compact plants having dark green and thicker leaves, and wider stem and root diameters. Investigating the underlying anatomical modifications in response to the treatment was the objective of the study. Plants of potato cultivar BP 1 were treated with 0, 45.0, 67.5, and 90.0 mg paclobutrazol per plant as a foliar spray. A month after treatment leaf, stem and root materials were taken from the control and plants treated with 67.5 mg paclobutrazol, and histological observations were made using light microscope. Leaves of treated plants showed an increased chlorophyll a and b contents, thicker epicuticular wax layer, elongated and thicker epidermal, palisade and spongy mesophyll cells. paclobutrazol increased stem diameter by about 58% due to induction of thicker cortex, larger vascular bundles, and wider pith diameter associated with larger pith cells. Widening the cortex and the induction of more secondary xylem vessels in response to paclobutrazol treatment increased the root diameter by about 52%. Paclobutrazol treatment remarkably increased the accumulation of starch granules in the stem pith cells and cortical cells of the stem and root. This study is similar to the other relevant studies in reporting an increased leaf thickness, and stem and root diameters; however, most of the underlying anatomical modifications described above have not been reported previously.

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D.R. Evert and D.A. Smittle

Nonterminal cuttings were taken just after leaf fall (November) from nongirdled shoots and from shoots girdled 7 weeks previously on `Flordaking', `Junegold', and `Harvester' peach trees [Prunus persica (L.) Batsch.]. Cuttings from nongirdled shoots rooted (85%) and survived (72%) better than did cuttings from girdled shoots on the same trees (64% rooting, 49% survival). Total sugar averaged across cultivars was 68 mg·g-1 dry weight in cuttings from nongirdled shoots and 82 mg·g-1 dry weight in cuttings from girdled shoots. Starch averaged 26 mg·g-1 dry weight and was independent of shoot girdling. `Flordaking' had the lowest starch concentration and the highest” percentage of cuttings that rooted and survived. Rooting and survival percentages differed by as much as 90% among trees within each cultivar.