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  • Author or Editor: Miklos Faust x
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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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Abstract

Detectable calcium accumulation of the tissue started at 10−3M of the bathing solution and increased with increasing concentrations thereafter. Calcium solutions of 10−3 to 10−1M were effective in inducing metabolic changes in tissue: they decreased respiration and increased protein synthesis. Much of the accumulated Ca (90%) could be exchanged from the tissue with Mg without changing the metabolic effect of the Ca. Although high concentration of Ca was needed to move metabolically active Ca into the site of its action, most of the Ca accumulated on exchange sites was metabolically inactive.

Open Access

Abstract

Examination of the fruit surface of the cvs. Golden Delicious, Delicious, and York Imperial, revealed considerable differences in the appearance of their wax structure. Waxes of ‘Delicious’ and ‘York Imperial’ were arranged in upright platelets early in the season and the platelets were somewhat smoothed by harvest. Wax of ‘Golden Delicious’ grown in a humid climate had surface cracks early in the season and the severity of the cracks had increased by harvest. The same cultivar grown in an arid climate was free of cracks. Waxes of this cultivar from both locations had amorphous wax with only occasional platelets.

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Abstract

Respiration of apples was inversely related to Ca content of flesh. Respiration increased markedly if Ca concn was below 110 ppm. High N levels also increased respiration. High Ca successfully counteracted the N effect and kept the respiration at a low level. When N was supplied as ammonium, respiration was higher than when a similar quantity of N was supplied as nitrate. Calcium counteracted the increased respiration induced by ammonium-N. Low Ca fruit lost 30-70% of its capacity to synthetize proteins and nucleic acids as measured by the incorporation of labelled valine and uracil. Low-Ca fruit was also high in ethanol insoluble solids, the major portion of which was probably cellulose. The effect of Ca on respiration can explain the negative relation between certain disorders (internal breakdown and watercore) characterized by overmaturity and Ca content of fruit.

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Abstract

Various pear species bloom at different times during the spring. Pyrus calleryana Decaisne is one of the earliest and P. communis L. is one of the latest blooming species. In 1975 there were 34 days between the earliest and latest blooming clones. When species or selections with different bloom times were crossed, two generations were needed to bring the bloom time of the progeny to the bloom time of the later blooming parent. The bloom of any given progeny occurred within only 4 to 5 days. No seedling in a progeny flowered later than the later blooming parent. Discovery of late blooming germplasm is essential for the development of late blooming types of pears.

Open Access

Abstract

Solution cultures altered with polyethylene glycol to induce a water stress of− 1.0 bar decreased net photosynthesis (Pn) and stomatal conductance (Cs) in the leaves of ‘York Imperial’ apple seedlings (Malm domestica Borkh.). Sprays with a complete nutrient solution produced similar responses and further decreased Pn and Cs in water-stressed plants. It appeared from the mesophyll conductance (Cm) calculation that reduction in Pn rate in water-stressed, as well as sprayed trees, was not caused solely by a stomatal factor. It is not known, however, whether nonstomatal limitation of Pn reflects a decreased capacity for CO2 fixation or increased light respiration, since mesophyll conductance was calculated assuming constant (zero) sink CO2 concentration in the leaf. In another experiment, decreasing to − 1.0 bar water potential of nutrient solution reduced daily water consumption and fresh weight of ‘York Imperial’ apple seedlings. Sprays with complete nutrient solution also tended to decrease daily water consumption of plants. Water stress decreased leaf Ca and root K and Mg concentrations, indicating that water stress may lower the absorptive capacity of the roots. However, water-stressed plants contained more Ca in the roots than unstressed plants, suggesting that lower leaf Ca concentration in stressed plants was caused by suppressed transport. Leaf sprays with complete nutrient solution increased Mg concentration in the leaves and stems and Ca concentration in the leaves.

Open Access

Abstract

‘York Imperial’ apple seedlings (Malus domestica Borkh.) grown in nutrient solution cultures with decreased water potential to− 1.0 bar by polyethylene glycol (PEG) increased water consumption, photosynthesis rate (Pn), and stomatal conductance (Cs). High light preconditioning of the plants used in this experiment was probably the reason why− 1.0 bar water potential in the nutrient solution was not low enough to induce apple seedling responses typical of water-stressed plants. However, application of PEG stress (−1.0 bar), to K-sprayed (K2SO4, −0.5%) trees lowered seedling water consumption Pn, and Cs. Potassium sprays alone did not significantly affect water consumption, Pn or Cs. When the water potential of the nutrient solution of PEG stressed plants was further decreased to −2.5 bars, unsprayed trees started to wilt within 2 days while sprayed trees did not. It is proposed that earlier stomatal closure of K-sprayed trees when stressed, already at low level of water stress (−1.0 bar), prevented plant water depletion when stress level was increased. This in turn delayed commencement of plant wilting. Potassium sprays also increased root:shoot ratio and root K concentration in PEG-stressed plants. These responses of K-sprayed trees could also contribute to greater tolerance to higher levels of water stress.

Open Access

Abstract

Low- and high-K pretreated ‘York Imperial’ apple seedlings (Malus domestica Borkh.) were grown in nutrient solution cultures. Addition of polyethylene glycol (PEG) to the nutrient solution to reduce water potential to −1.0 bar reduced water consumption, fresh weight, specific leaf weight (SLW), and leaf water potential and increased the amount of water consumed per unit of fresh weight gain. High-K pretreatment increased water consumption of unstressed seedlings but decreased water consumption of PEG-stressed plants. Daily sprays with 0.5% KCl applied in early afternoon had no effect on water consumption rate in apple seedlings. However, sprays probably induced wider stomatal opening, since K-sprayed trees had lower leaf water potential when measured at noon than unsprayed trees. This effect was not observed when water potential was measured in the morning (0800 hr). High-K plants had higher leaf water potential than low-K plants in the morning. Potassium pretreatment and PEG stress as well as K-sprays had numerous effects on plant mineral composition. The K-pretreatment or K-sprays did not alleviate the detrimental effects of PEG-induced water stress despite the effects of K-pretreatment and K-sprays on mineral composition and leaf water potential.

Open Access

The activity of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphate gluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (ICDH), pyruvate kinase (PK), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were studied in apple (Malus domestics Borkh.) buds during dormancy and thidiazuron-induced budbreak. When buds were dormant, the activity of the glycolytic enzymes GAPDH and PK and the tricarboxylic acid (TCA) cycle enzyme ICDH was low compared to that in nondormant buds. The activity of these enzymes increased during budbreak, peaked when buds were in the green tip stage just before the start of rapid expansion (at 8 days after thidiazuron treatment), and declined thereafter. The activity of pentose-phosphate cycle enzymes G6PDH and 6PGDH was higher in dormant buds than in nondormant buds. 6PGDH was about twice as high as G6PDH. During budbreak and resumption of growth, G6PDH and 6PGDH activity decreased.

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The effects of thidiazuron on changes in superoxide dismutase (SOD) activity in apple (Malus domestica Borkh cv. York Imperial) buds during dormancy break were determined. Dormant buds had low SOD activity. Increased SOD activity was correlated with budbreak induced by thidiazuron. Buds contained three distinct forms of SOD: Cu, Zn-SOD; Mn-SOD; and Fe-SOD. Most of the SOD activity in apple buds was attributed to Cu and Zn-SOD, followed by Mn-SOD. Iron-SOD was not present in dormant buds, and only a trace amount was found as buds started rapid expansion. Chemical name used: N-phenyl-N′-1,2,3,-thidiazol-5-ylurea (thidiazuron).

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