Search Results
Abstract
The compositional changes occurring in the cell wall of maturing and ripening pear fruits (Pyrus communis L. cv. Spadona) were examined in relation to the activity of pectolytic enzymes and cellulase. Fruit softening was accompanied by a rise in water and EDTA-soluble pectic fractions, and in free galacturonic acid. The latter reached peak levels after 15 weeks of cold storage and thereafter declined. Simultaneously with the degradation of pectin there was a 4 to 5 fold increase in polygalacturonase activity, but pectin-methyl-esterase activity declined as it did throughout the harvest and storage seasons. Cellulase activity which was present also in immature fruit increased 2 to 3 fold as the fruit softened, but in the last stages of softening it decreased. Treatment of the firm fruit with partially purified preparations of cellulase and polygalacturonase both caused a dissolution of insoluble pectin material.
Abstract
The abscission zone of Douglas-fir (Pseudotsuga menziesii var. menziesii Mitb. Franco) was studied throughout needle development. A separation layer one cell thick developed at the needle base when extension growth ceased. Cells of this layer stained positively with safranin and slightly with toluidine blue. A protective layer, which developed in stem tissue adjacent to the separation layer, stained positively with safranin, periodic acid-Schiff's reagent, phloroglucinol-HCL and chlorine sulfite. Abscission was induced by drying cut trees to a water potential below −3.5 MPa. Water-stressed trees segregated into abscising and non-abscising needle groups. Walls of separation layer cells from trees with abscising needles were characterized by shrinkage followed by tearing. Walls of separation layer cells from trees with non-abscising needles were anatomically unaffected by water stress. Mechanical damage of cell walls in the separation layer occurred when water stress was −3.5 MPa or lower. Abscission could be prevented by maintaining a water potential above −3.5 MPa.
Abstract
Suspension-cultured pear (Pyrus communis ‘Bartlett’) cells cold-acclimated during exposure to 2°C. Cold acclimation was accompanied by changes in soluble extracellular polysaccharides and in the deposition of callose in the cell wall. Release of a relatively small neutral polysaccharide into culture medium was increased at 2°. However, low temperature decreased the extracellular accumulation of a larger molecular weight (M r) pectic polysaccharide. The reduced amount of pectic polysaccharide may have been the result of both a low-temperature-enhanced degradation of existing polysaccharide and an inhibition of new synthesis or secretion. The effect of low temperature on callose deposition was observed using an aniline blue fluorescent staining procedure. Pear cells held at 2° showed far more intense staining than those at 22°, indicating increased deposition of callose or other β-1,3-glucans at the cell surface during cold acclimation.
Abstract
The physiological changes occurring in green and red bell pepper fruit (Capsicum annuum L. ‘Maor’) before and after harvest were investigated. Red pepper at harvest was less firm and had lower water potential, lower insoluble pectins, and higher water-soluble pectins than green bell pepper. However, the changes occurring in both types of peppers after harvest were similar. Postharvest weight loss was accompanied by a decrease in firmness, decrease in water potential, decrease in insoluble pectin, and an increase in soluble pectin in the cell wall. The production of CO2 showed that there was a slight decrease and a significant but small increase of ethylene after harvest. If weight loss was retarded by holding pepper in a water-saturated atmosphere, then all of these physiological changes were prevented or markedly slowed. It appears that water stress hastens and possibly triggers the onset of senescence in harvested bell pepper fruit.
Abstract
The ultrastructural localization of polysaccarides in Malus domestica Borkh. leaf cuticles was investigated by electron microscopy staining. The cuticle/cell wall interface was not stained by ruthenium red or hydroxylamine-ferric chloride, indicating the lack of a distinct pectin layer. The inner region of the cuticle was intensely and uniformly stained by phosphotungstic acid (PTA) and was lightly stained by silver proteinate, indicating the presence of polysaccharides, which in part may be pectin as indicated by staining with ruthenium red. Fibrils in the inner region of the cuticle were not stained by ruthenium red, hydroxylamine-ferric chloride or silver proteinate, but appeared lightly stained by PTA; this suggests by deduction that the fibrils may consist of cutinized cellulose. The outer region of the cuticle was not stained by any of the staining procedures, indicating the lack of polysaccharides.
Abstract
A procedure is described for studying routes of liquid entry into and movement within pickling cucumber fruit (Cucumis sativus L. cv. Chipper). The internal gases of the fruit are exchanged with oxygen in a closed container. Fruit are then covered with 0.5% aqueous safranin O and allowed to stand for a few hours. Liquid was shown to enter the fruit through epidermal regions of greatest stomatal density, which are near placental tissue. The dye solution then moved through intercellular spaces and cell walls of placental and other mesocarp tissues and vascular elements. The stain facilitated delineation of stomata and visual observation of routes of liquid movement. Liquid entrance apparently is induced due to a partial vacuum created within the O2-exchanged and liquid-submerged fruit.
Abstract
A comprehensive analysis of fruit water relations and the extensibility of the dermal tissue (skin) of Vitis vinifera cv. Cardinal berries was conducted throughout the period of biphasic growth. The pattern of berry growth was not coordinated with the patterns of berry water potential or turgor. It was anticipated, therefore, that cell wall extensibility and yield threshold varied during berry development. Measurements of uniaxial extensibility of dermal strips removed from berries indicated that total and plastic extensibility were relatively constant during stages I and II of berry growth, but increased significantly in the transition from stage II to stage III. The functional interrelationships between sugar accumulation, skin extensibility, and berry growth, which increases at the onset of stage III, remain to be elucidated.
Abstract
Berry/pedicel abscission zone formation in cultivated highbush blueberry (Vaccinium corymbosum L.) during fruit ripening appeared at the distal portion of the transition zone (disc) separating the berry and the pedicel. The abscission zone was first evident as a compressed zone of cells at the periphery of the berry/pedicel junction in the immature green stage of berry development. Cell separation initially appeared during the green-pink berry stage concomitant with berry coloration. Separation was characterized primarily by cell wall rupture. No separation layer was formed through either the berry epidermis or the vascular bundles. The number of berries without attached pedicels separating from the cluster under applied force was closely related to the stage of ripening of the fruit. Stresses imparted during ripening by rupturing internal tissues are evident in definite morphological changes appearing on the surface of the fruit.
Abstract
A technique is described whereby osmotic potential, turgor potential and total fruit water potential can be determined quickly in the field with the aid of a pressure bomb, a hand held refractometer, and a percent soluble solids to osmotic potential conversion chart. A unique inverse linear relationship between percent soluble solids and osmotic potential was found for each fruit species. Application of this technique to rain cracking of ‘Napoleon’ sweet cherries (Prunus avium L.) shows that cracking is not strictly related to percent soluble solids, osmotic, turgor, or fruit water potential. This suggests that the degree of cuticular permeability, cuticular strength, cell wall strength or other factors may be of greater importance in determining cracking susceptibility than water potential parameters.
Abstract
The ultrastructure of floral abscission zone cells of Phaseolus vulgaris L. cv. Dark Red Kidney was studied in order to relate changes in fine structure to known changes in morphology and physiology of the foliar abscission zone of Phaseolus and to the fine structure of floral abscission zones of other plants. Major structural changes in cell walls are similar in abscission zones of senescing leaves and post-anthesis flowers but the rapidity of cellular changes is greatly accelerated in the latter. Inclusions typically found in floral abscission zone cells of Solanaceous plants are not present in Phaseolus floral abscission zone cells. Cellular changes are evaluated in terms of their potential relationship to the abscission process.