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Sriyani Rajapakse, Janice Ryan-Bohac, Sasanda Nilmalgoda, Robert Ballard and Daniel F. Austin

The sweet potato Ipomoea batatas (L.) Lam. is classified in series Batatas (Choisy) in Convolvulaceae, with 12 other species and an interspecific true hybrid. The phylogenetic relationships of a sweetpotato cultivar and 13 accessions of Ipomoeas in the series Batatas were investigated using the nucleotide sequence variation of the nuclear-encoded β-amylase gene. First, flowers were examined to identify the species, and DNA flow cytometry used to determine their ploidy. The sweetpotato accession was confirmed as a hexaploid, I. tabascana a tetraploid, and all other species were diploids. A 1.1–1.3 kb fragment of the β-amylase gene spanning two exons separated by a long intron was PCR-amplified, cloned, and sequenced. Exon sequences were highly conserved, while the intron yielded large sequence differences. Intron analysis grouped species currently recognized as A and B genome types into separate clades. This grouping supported the prior classification of all the species, with one exception. The species I. tiliacea was previously classified as a B genome species, but this DNA study classifies it as an A genome species. From the intron alignment, sequences specific to both A and B genome species were identified. Exon sequences indicated that I. ramosissima and I. umbraticola were quite different from other A genome species. Placement of I. littoralis was questionable: its introns were similar to other B genome species, but exons were quite different. Exon evolution indicated the B genome species evolved faster than A genome species. Both intron and exon results indicated the B genome species most closely related to sweetpotato (I. batatas) were I. trifida and I. tabascana.

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Donald E. Irving, Glen J. Shingleton and Paul L. Hurst

Extractable activities of α-amylase, β-amylase, and starch phosphorylase were investigated in order to understand the mechanism of starch degradation in buttercup squash (Cucurbita maxima Duchesne ex Lam. `Delica') with the ultimate goal of improving the conversion of starch into sweet sugars. During rapid starch synthesis (0 to 30 days after flowering), extractable activities of α-amylase and β-amylase were low, but those of starch phosphorylase increased. After harvest, during ripening at 12 °C, or in fruit left in the field, activities of α-amylase and β-amylase increased. Starch contained 20% to 25% amylose soon after starch synthesis was initiated and until 49 days after harvest irrespective of whether the crop remained in the field or in storage at 12 °C. Maltose concentrations were low prior to harvest, but levels increased during fruit ripening. Data suggest starch breakdown is hydrolytic in buttercup squash, with α-amylase being the primary enzyme responsible for initiating starch breakdown.

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Ruth Lavon, Eliezer E. Goldschmidt, Rafael Salomon and Andre Frank

Carbohydrate content and related enzyme activities were determined in leaves of rough-lemon (Citrus volkameriana Ten. & Pasq) plants grown under K, Mg, and Ca deficiencies. Starch content was lower and soluble sugar significantly higher in K-deficient than in control leaves. Magnesium- and Ca-deficient leaves, on the other hand, accumulated large amounts of starch. Electron micrographs also showed a reduction in the number and size of starch grains in chloroplasts of K-deficient leaves, while those of Mg- and Ca-deficient leaves were filled with large starch grains. Total amylase activity increased 3- to 7-fold in K-deficient leaves, with maltose as the major product and small amounts of maltotriose. Electrophoretic separation of amylase isozymes on native gels containing starch or amylopectin showed higher band intensities in K-deficient leaves. Examination of the capacity of leaf extracts to use amylopectin vs. β-limit dextrin indicated that mainly 8-amylase was involved. Acid invertase activity increased 7-fold in K-deficient leaves, while alkaline invertase showed little change.

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Vital Hagenimana, Ronald E. Simard and Louis-P. Vézina

In vitro activity measurements indicate that storage sweetpotato roots contain high amounts of extractable amylolytic enzymes. These storage roots also have a very high starch content, a characteristic indicating that the in vitro measurements estimate potential amylolytic activity rather than actual physiological activity. We are interested in optimizing the use of endogenous amylases when processing sweetpotato roots and have undertaken a study to identify physiological parameters that control in vivo starch breakdown. Sweetpotato roots were allowed to germinate for 35 days in controlled conditions. Using a combination of in vitro activity measurements and immunochemical detection, the spatial distribution and changes in activity levels for the three major amylolytic enzymes in storage sweetpotato roots—α-amylase, β-amylase, and starch phosphorylase—have been followed. After 6 days, α-amylase protein increased in the outer starchy parenchymatous tissues surrounding the cambium layers, a result suggesting a de novo synthesis of the enzyme in cambium or laticifers layers. β-Amylase was abundant throughout the root at all times, and its high levels did not directly affect starch degradation rates. Starch phosphorylase protein level remained constant, while its extractable activity increased. Starch content decreased during sweetpotato seed root germination. However, the amount of starch that disappeared during germination was low compared with the calculated starch hydrolysis potential estimated by amylolytic activity measurements.

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Yu Sung*

Germination of `Fond May' eggplant seeds at 25°C could be increased by after-ripening fruit or fresh seed treated with KNO3 or GA3 or priming. There were high amount of starch and low amount of soluble sugar in after-ripening seed or primed seed. The amount of soluble sugar in after-ripening seed was higher than that in control seed before the radicle protrusion at 25 °C and 25/30 °C. Starch amount in after-ripening seed imbibed at 25/30 °Cwas significantly high. Soluble sugar in un-after-ripening seed imbibed at 25 °C for 2-3 days had higher amount and the high activity of β-amylase was appeared in the second days. Activity of amylase in primed seed imbibed at 25 and 25/30 °C for 3 days increased. The activity of endo-β-mannanase was high in after-ripening or priming or GA3 treated seed at 25 °C.

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Russell Pressey

Chinese water chestnuts retain crispness during heating much better than most vegetables. To help explain this unusual property of water chestnuts, a study was conducted to determine their cell wall composition and to assay some of the enzymes that may be involved in hydrolysis of cell walls and starch. Water chestnuts were found to contain high levels of β-1,3-glucanase and β-glucosidase but low cellulase. A number of other enzymes were detected including invertase, α- and β-galactosidases and α-mannosidase. A rather high level of amylase is present in water chestnuts and most of the activity appears to be due to β-amylase. Water chestnuts contain low pectinesterase but a moderate amount of polygalacturonase which was purified and characterized. It is an exoenzyme that does not require Ca2+ for activity in contrast to most other exopolygalacturonases. An unusual property of the water chestnut polygalacturonase is its stability to heat, with retention of most of its activity after heating at 80°C for 5 min. The cell walls of water chestnuts contain low pectin which is solubilized slowly by pectic enzymes.

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Haiyan Zhang

increase of β-amylase activity in seeds, which could promote seed germination under salt stress ( Duan et al., 2007 ), osmotic stress ( Zhang et al., 2003 ), and normal conditions ( Zhang et al., 2005 ), indicating that NO is involved in the intrinsic

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Teresa Eileen Snyder-Leiby and Shixiong Wang

, data indicate that α-amylase is less important for starch breakdown and other enzymes, including β-amylase and cytosolic disproportionating enzyme-like protein, are necessary to mobilize starch from the chlorosplast ( Lloyd et al., 2005 ; Smith et al

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Na Zhang, Lu Han, Lixin Xu and Xunzhong Zhang

of ethephon and gibberellin A3 on Amaranthus caudatus seed germination and α- and β-amylase activity under salinity stress Acta Biologica Cracoviensia 51 2 119 125 Bialecka, B. Kepczynski, J. 2010 Germination, α-, β-amylase and total dehydrogenase

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Naveen Kumar, Fnu Kiran and Ed Etxeberria

-glucose pyrophosphorylase in HLB-affected roots ( Zhong et al., 2015 ). In addition, suppression of β-amylase 3 (which converts amylopectin into maltose), β-amylase 6 , and sucrose synthase 3 (which converts sucrose into uridine diphosphate glucose and fructose) has