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Abstract

Fresh, unfixed meristems of rose (Rosa hybrida L.) were viewed in the scanning electron microscope to determine the morphological differences and organogenesis of flowering and blind shoots. Gluteraldehyde fixed, ethanol dehydrated and critical point dried tissue was severely desiccated with individual cell walls becoming concave. Fresh tissue remained turgid for at least 10 min in the microscope. Visible signs of flower initiation were evidenced by the presence of sepal primordia followed by differentiation of petals, anthers and stigma. No evidence of flower initiation was observed in the blind shoot.

Open Access

Abstract

Structural differences in leaves of pecan [Carya illinoensis (Wang) K. Koch] of cultivars resistant and susceptible to the scab pathogen, Cladosporium caryigenum (Ell. et Lang) Gottwald com. nov (formerly designated Fusicladium effusum Wint.), were examined using scanning and transmission electron microscopy. In immature leaf tissue, cultivar resistance was correlated with fewer peltate glandular trichomes, a greater frequency of collapsed trichomes, and abundant phenolic compounds in the palisade parenchyma and bundle sheath cells compared to susceptible cultivars. In mature, scab-resistant leaves of all cultivars, trichomes were collapsed and less numerous, phenolics were abundant, and cuticular and epidermal cell wall development was greater compared to that of immature leaves.

Open Access
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Abstract

Naphthaleneacetic acid (NAA) thinning sprays applied at appropriate intervals and dosage levels to 3 apple cultivars, verified the existence of a critical stage during which developing fruitlets were maximally sensitive. Average fruit diameter accurately identified NAA-sensitivity, but the index varied among cultivars. Polynomial regression analyses revealed a direct relationship between diameters of individual fruit samples and thinning response for each experimental unit. NAA-induced fruit abscission was usually maximal 2 to 3 days prior to the onset of cytokinesis in the endosperm. Cell wall formation did not invariably signify an end to the induction of significant abscission.

Open Access
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Abstract

Cracking behavior of tomato skins (Lycopersicon esculentum Mill.) was investigated using failure and relaxation tests. Skin specimens were taken in 2 directions to represent concentric and radial cracks. Normal tissue and tissue subjected to mechanical forces were examined to determine the resulting histological distortions. The relaxation test gave more information than the failure test. No difference was observed for longitudinal or transverse skin strength for failure or the relaxation test indicating isotropic behavior. The shape of the cells and deposition of cuting appeared to affect cracking behavior. Generally, cells elongated and flattened during the failure test and failed between cells walls.

Open Access

Abstract

Abscission layer formation during fruit maturation of sour cherry, Prunus cerasus L., occurred between the fruit and the pedicel. No abscission layer was formed between the pedicel and the spur. The abscission layer was first evident 12-15 days before fruit maturity. This layer was composed of 5-8 rows of cells in the transition zone between the fruit and pedicel and was first identified by its low affinity for haematoxylin. Cell separation occurred without rupturing of cell walls. Later cell wall collapse was apparent. Cells immediately distal and proximal to the line of separation were thin walled and prone to separate easily. No abscission layer was formed through the vascular bundles and no cell division was noted during layer formation. Abscission layer formation was observed in detached sour cherry fruit which was histologically similar to that observed in vivo. There was a close relationship between abscission layer formation and force required to separate the fruit from its pedicel. No abscission layer was observed, in the transition zone between the fruit and pedicel in the sweet cherry, Prunus avium L.

Open Access

Abstract

Capsicum annuum (‘Early Calwonder’) seeds germinated (radicle protrusion) in 8 days at 15°C and 4 days at 25°. The seeds have an endosperm 7 to 9 cells in thickness which lies directly in front of the radicle. The external appearance of the endosperm did not change until one day before radicle emergence, when the endosperm in front of the radicle enlarged and protruded outward. This change was accompanied by breakdown and loss of endosperm cellular integrity and reduction in endosperm thickness directly in front of the radicle, but not in other regions of the endosperm. Gibberellic acid (GA4+7) decreased the time for appearance of the protruding endosperm and radicle protrusion through the seed coat by one day. Cell wall degrading activity was detectable during the early stages of germination and became extremely high after radicle emergence. Seeds treated with 100 ppm GA4+7 showed slightly increased enzyme activity during early germination and differences became more pronounced as germination progressed. Cellulase activity was not found in the extracts, but seed enzyme preparations degraded a galactomannan substrate. The enzyme exhibited only endohydrolytic activity, indicating an enzyme which may participate in the weakening of cell wall. It was postulated that an endomannanase is needed for endosperm breakdown in front of the radicle in order for rapid germination of pepper to occur. A reduction in germination temperature from 25° to 15° reduced the rate of radicle movement through the seed coat by one half.

Open Access

Abstract

A range of tomato (Lycopersicon esculentum Mill.) cultivars was examined for changes during ripening in firmness, endopolygalacturonase (PG) activity and the molecular forms of polygalacturonase, Ca concentration, and the extractability of the Ca. Firm cultivars were firmer than the soft cultivars throughout ripening, and generally they contained less PG activity at each stage examined. In all cultivars, PG was predominately or entirely in the high molecular weight form (PG1) early in ripening, with the PG2 forms being increasingly prominent as ripening progressed. Differences in firmness were established while PG1 was the predominant PG. Uronic acid polymers in isolated cell walls were degraded rapidly by endogenous PG when citrate was present to complex Ca. In the presence of sufficient citrate, cell wall uronic acids of a firm and soft cultivar were equally susceptible to hydrolysis, suggesting that differences in the digestion of the walls by PG were dependent upon differences in Ca content or distribution. However, neither total, water, nor saline-extractable Ca showed consistent correlations with fruit firmness, and they also showed no progressive change during ripening.

Open Access

Abstract

Histogenetic studies of the young fruit revealed that incipient cork spot in ‘York Imperial’ apples (Malus domestica Borkh.) may appear as early as 3 weeks after fruit set, and that it initially becomes evident as a sporadic gradual necrosis of several parenchymatous cells of the outer cortex. About 1 month later, healthy enlarging cortical cells contiguous to the necrotic region undergo a redifferentiation via direct nuclear or amitotic divisions that result in a promiscuous intracellular proliferation of daughter cells. These remain within the confines of the original mother cell wall until it ruptures. The amitotic nuclei assume a variety of configurations and divide by cleavage. The method by which cell walls form between the intracellular proliferations is undetermined, and there is no evidence of cell plate formation. Once initiated, cork spot proliferation occurs only within the parenchymatous cells of the fruit cortex and is continuous throughout the growing season. There is no evidence of an internal cork cambium per se. Cork spot is not invariably associated with the vascular bundles, and there is no distinct evidence of the senescence of vascular bundles resulting principally from the necrosis. The necrotic condition becomes visible externally as a slightly sunken epidermal discoloration about 3 months after fruit set.

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of seed tannins was intact ( Fig. 2C ). The most prominent characteristic of the seed surface was polygonal (almost hexagonal) reticulum (network) formed by epidermal cells with thick cell walls ( Fig. 2D–E ). Fig. 1. Photographs of a ( A ) healthy

Free access

-1200; K. Schriever, Schleif- and Poliermittel, Hamburg, Germany). To ensure complete removal of the CM and minimize damage of the cell walls of the underlying epidermal cells, the procedure was optimized in preliminary experiments by monitoring uptake

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