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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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Anna Marín, Anne Plotto, Lorena Atarés and Amparo Chiralt

time, respectively. C = control (water dispersion); CFU = colony-forming unit; LAB = L. plantarum ; NaC = sodium caseinate, OA = oleic acid; PS = pregelatinized potato starch. After 7 d of storage, the survival of L. plantarum showed a significant

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Seong-Tae Choi, Doo-Sang Park, Seong-Mo Kang and Seong-Koo Kang

; Park et al., 2003 ). The reserve N compounds are present as amino acids and proteins and the reserve carbohydrates as soluble sugars and starch ( Cheng et al., 2004 ; Oliveira and Priestley, 1988 ; Titus and Kang, 1982 ). A negative relationship

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Guoqiang Hou and Jack W. Buxton

Through control of light intensity and CO, concentrations, three levels of starch (low, medium and high) in marigold seedlings existed at sunset. The range in starch concentration represented that encountered under average greenhouse conditions. For each starting starch concentration, an optimum temperature was initially determined based on first and second order reactions on the corresponding starch decline curve. Every day, during seedling growth in the greenhouse, the starch concentration at sunset was predicted based on primarily the quantity of light received throughout the day; the night temperature was adjusted to the predicted optimum night temperature setting. Based on these studies a significant improvement in seedling growth can be achieved with significantly less heating cost.

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Yung-Kun Chuang, I-Chang Yang, Chao-Yin Tsai, Jiunn-Yan Hou, Yung-Huei Chang and Suming Chen

competition of international markets. Previous studies have indicated that carbohydrates, hormones, and minerals are related to the growth of Phalaenopsis plants ( Chen et al., 1994 ; Kataoka et al., 2004 ). Among them, starch is one type of carbohydrate

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Rui Zhou, Lailiang Cheng and Abhaya Dandekar

The reaction catalyzed by ADP-glucose pyrophosphorylase (AGPase) to form ADP-glucose is a regulatory and rate-limiting step in starch synthesis in plants. In response to decreased sorbitol synthesis, starch synthesis was up-regulated in the transgenic apple plants. In this study, we examined both redox and metabolite regulation of AGPase to understand the mechanism responsible for the up-regulation of starch synthesis. No difference in the monomerization/dimerization of apple leaf AGPase small subunits was observed between the transgenic plants and the untransformed control. NADP-dependent malate dehydrogenase, indicative of chloroplastic redox status, did not show significant change in the transgenic plants either. Determination of key metabolites with nonaqueous fractionation indicated that concentrations of hexose phosphates (mainly glucose-6-phosphate and fructose-6-phosphate) were higher in both the cytosol and chloroplasts of the transgenic plants than in the control, whereas 3-phosphoglycerate (PGA) concentration in the chloroplast was not higher in the transgenic plants. We conclude that accumulation of hexose-phosphates results in a decrease in inorganic phosphate (Pi) concentration and an increase in PGA/Pi ratio in the chloroplast, leading to up-regulation of starch synthesis via activating AGPase.

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Richard C. Rosecrance, Steven A. Weinbaum and Patrick H. Brown

The effect of crop load on nutrient and starch storage in mature, alternate-bearing pistachio trees was examined. Tree storage pools were estimated from the differences in nutrient and starch contents of perennial tree parts between dormancy (the period of highest nutrient and starch content) and following spring flush (the period of lowest nutrient and starch content). Following a lightly cropping (off) year, trees contained significantly larger N, P, and K storage pools than following a heavily cropping (on) year. The relative contribution of leaf nutrient resorption to tree nutrient storage pools varied depending on the crop load. Nutrient storage is a function of net leaf nutrient resorption and current uptake from the soil. Leaf nutrient (N, P, and K) resorption was a more significant component of nutrient storage in on-year than off-year trees. The contribution of nutrient storage to shoot (i.e., leaves, fruit, current-year wood) nutrient contents was evaluated following the spring flush (May) and nut fill (September) periods. Nutrient storage pools are an important source of nutrients during the spring flush of growth, but nutrient demands during nut fill are met primarily by current nutrient uptake from the soil. The relationships between nutrient storage and uptake are discussed.

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Gary W. Stutte, Neil C. Yorio and Raymond M. Wheeler

The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of `Norland' potato (Solanum tuberosum L.) was determined under high (412 ∝mol·m-2·s-1) and low (263 ∝mol·m-2·s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 μmol·m-2·s-1, and leaf starch increased from 70 to 129 and 118 mg·g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 μmol·mol-1) or CO2 saturation point (1100-1200 μmol·mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (≈15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (≥12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon, then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.

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K.I. Theron and G. Jacobs

Flowering-size Nerine bowdenii bulbs were sampled from a commercial planting at 2-week intervals from 13 Aug. 1991 to 14 June 1992. They were dissected, the dry weight of foliage and leaf bases was recorded, and carbohydrate analysis was performed on the foliage leaves, leaf bases, and roots. Starch was the dominant storage carbohydrate, and leaf bases were the principal bulb structures where it was stored. Changes in starch content closely followed dry weight changes in the bulb. When exposed to low temperatures, starch was converted to sugars. Except for these high levels in the leaf bases, sugars, expressed both as concentration and total content, were low in bulb components, indicating continued export and conversion to starch. Low sugar levels during the period that florets in the current season's inflorescence develop to stage Late G (gynoecium elongated, carpels fused) is implicated in the abortion of the inflorescence.