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Miklos Faust

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Miklos Faust

At the beginning and near to the end of the endodormant period, cytokinin-type growth regulators are effective to end dormancy in apple. The same growth regulators are not effective during the middle of this period. Terminal buds require less chilling than lateral buds to emerge from the dormant period. Lateral buds on decapitated shoots also require less chilling, indicating that auxin may be involved in dormancy. Replacing the terminal with IAA keeps water in bound state in the lateral buds, indicating the effect of IAA in dormancy. We have developed the theory that the beginning and the end of the winter-dormant period is governed by apical dominance. It appears that only this period can be manipulated either with dormancy avoidance methods or with dormancy-breaking chemicals. The central portion of the dormant period is not subject to manipulation. Therefore, it is important that the depth of the dormancy is quantified. Certain growth regulators can be used for determining the state of bud dormancy. Thidiazuron gives results within 2 to 4 days.

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Shiow Y. Wang and Miklos Faust

Composition changes in galactolipids, phospholipids, and sterols in apple shoots (Malus domestica Borkh. cv. Red Delicious) from August to April were determined. The predominant fatty acids in the membrane lipids of apple shoots were palmitic acid (C16:0), linoleic acid (C18:2), and linolenic acid (C18:3). The major galactolipid components in apple shoots were monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG). The amount of MGDG and DGDG increased from autumn to spring. Galactolipids contained highly unsaturated fatty adds, mainly linoleic (18:2) and linolenic (18:3) acid. The major individual phospholipids were phosphatidylcholine (PC) and phosphatidylethaeolamine (PE). β -Sitosterol and sitosteryl ester were the predominant sterols. The phloem contained higher amounts of galactolipids, phospholipids, and sterols than did the xylem tissue. There was a significant increase in the content of galactolipids and phospholipids and onsaturation of their fatty acids during cold acclimation. A decrease in the ratio of free sterols to phospholipids also occurred in apple shoots toward cold winter months. Composition changes in galactolipids, phospholipids, and sterols that were associated with growth cessation, defoliation and cold acclimation from fall to winter, were mostly reversed following deacclimation in spring.

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Shiow Y. Wang and Miklos Faust

The changes of membrane lipids in apple (Malus domestics Borkh. cv. Delicious) auxillary and terminal buds from August to April were determined. The predominant lipids were monogalactosyl diglyceride (MGDG), digalactosyl diglyceride (DGDG), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). An increase in membrane polar lipids was associated with budbreak and bud growth from August to April. Linolenic acid was the predominant fatty acid in MGDG, DGDG, and PC, while linoleic acid was predominant in PE. Phosphatidylglycerol (PG) and phosphatidylinositol (PI) contained a high amount of palmitic acid. The ratio of (18:2 + 18:3) to 18:1 fatty acids in galactolipids in apple buds increased from August to April. ß-Sitosterol and sitosteryl ester were the predominant sterols in apple buds. An increase in sitosterol, a decrease in sitosteryl ester, and a decline in the ratio of free sterols to phospholipids occurred during budbreak in spring. A decrease in sitosterol was associated with bud expansion in spring.

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Shiow Y. Wang and Miklos Faust

Ethylene biosynthesis and polyamine content were determined in normal and watercore-affected apple (Malus domestics Borkh. cv. Delicious). Fruit with watercore produced more ethylene and contained higher amounts of putrescine (PUT), spermidine (SPD), 1-aminocyclopropane-1-carboxylic acid (ACC), and 1-(malonylamino) cyclo-propane-1-carboxylic acid (MACC). The activities of ACC synthase and ethylene-forming enzyme (EFE) in watercore-affected fruit were also higher than in normal fruit. The EFE activity in severely affected flesh was inhibited, resulting in ACC accumulation and low ethylene production. S-adenosylmethionine (AdoMet) was maintained at a steady-state level even when C2 H4 and polyamides were actively synthesized in normal and affected fruit.

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Shiow Y. Wang and Miklos Faust

The ability of low and high temperatures to overcome endo- and paradormancy along with the possible mechanisms involved in these treatments for breaking apple (Malus domestica Borkh. `Anna') bud dormancy were studied. All these treatments induced budbreak in paradormant (in July) and endodormant (in October) buds. Cold and heat treatments increased ascorbic acid, the reduced the form of glutathione (GSH), total glutathione, total non-protein thiol and non-glutathione thiol, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased. The treatments also increased the ascorbic acid: dehydroascorbate and GSH: GSSG ratios and the activity of ascorbate-free radical reductase, ascorbate peroxidase, dehydroascorbate reductase, ascorbate oxidase, and glutathione reductase in the buds. These results indicate that budbreak induced by cold and heat treatments is associated with the removal of free radicals through activated peroxide-scavenging systems.

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Shiow Y. Wang and Miklos Faust

The activity of ascorbic acid oxidase (AAO) was studied in apple (Malus domestica Borkh.) buds during dormancy and thidiazuron-induced budbreak. In dormant buds, activity of AAO was low compared with buds that were treated with thidiazuron and had resumed growth. An increase in AAO activity began at the time of metabolic transition from dormancy to budbreak. The highest level of activity was reached 10 days after thidiazuron induction during the expansion growth phase. In vitro AAO activity of apple bud extract was increased by addition of Cu (CuSO) and inhibited by Cu-chelating agents, diethyldithiocarbamate (DDC), sodium azide (NaN), and 8-hydroxyquinoiine (8-OH-Q). In vivo treatment of apple buds with Cu-chelating agents inhibited AAO activity and bud growth but not budbreak. Chemical name used: N- phenyl -N' -1,2,3-thidiazol-5-ylurea (thidiazuron).