Search Results
Apple (Malus domestica Borkh.) trees are often affected by a severe June fruit drop, which is often correlated with competition phenomena involving fruit nutrition. This research was initiated to determine if June drop in `Gloster'/M.9 apple could be correlated with a diminished nutrient availability in developing seeds and fruit. During the test period [30 to 62 days after full bloom (AFB)], the fruit that abscised had a diameter similar to that reached by persisting fruit 13 days earlier. Biochemical parameters related to nutritional status of fruit were measured when an abscission peak occurred 38 days AFB. Persisting fruit (control) and abscised fruit were compared along with fruit that abscise 13 days later. The cortex tissue obtained from the two kinds of abscised fruit showed a higher level of soluble reducing sugars and sucrose and a lower content of K+, acid hydrolyzable polysaccharides, and protein compared to the control. Further, the Ca2+ content was higher in abscised fruit than in controls of the same age, whereas there was no difference when fruit of the same size were compared. Total amino acid level was similar in control and abscised fruit at the same age, but there was a lower amino acid level in abscised fruit of the same size. Histological analysis of cortex tissue indicated that abscised fruit have larger cells with less evident nuclei and thinner cell walls than controls. Compared to control fruit, abscised fruit showed the same average number of seeds and a severe inhibition of seed growth; seeds from both kinds of abscised fruit had the same or higher levels of the parameters measured. No positive correlations were observed between fruit abscission and nutrient content of seeds or fruit.
Sugar accumulation and the activities of sugar metabolizing enzymes were related to the occurrence of pineapple [Ananas comosus (L.) Merr.] flesh translucency. During early fruit development, glucose and fructose were the predominant sugars. Sucrose began to accumulate 6 weeks before harvest at a higher rate in the fruitlet than in the interfruitlet tissue. Electrolyte leakage from pineapple flesh increased rapidly from 6 weeks before harvest and paralleled sucrose accumulation. Sucrose synthase activity was high in young fruit flesh and declined with fruit development, while the activity of sucrose phosphate synthase was relatively low and constant throughout fruit development. The activities of acid invertase, neutral invertase, and cell-wall invertase (CWI) were high in the young fruit flesh and declined to very low levels 6 weeks before harvest when sucrose started to accumulate. CWI activity increased again, more in the fruitlet than in the interfruitlet tissue, 4 weeks before harvest. Removal of 1/3 of the plant leaves 3 weeks before harvest significantly reduced fruit flesh total soluble solids, CWI activity, and translucency incidence at harvest. The activity of CWI in translucent fruit flesh was significantly higher than in opaque fruit flesh at harvest. CWI activities in the basal section of pineapple flesh and in the fruitlet, where translucency first occurred, were higher than those in the apical section and in the interfruitlet tissue, respectively. Results support the hypothesis that high CWI activity in pineapple flesh at the later stage of fruit development enhances sucrose unloading into the fruit flesh apoplast, leading to increased apoplastic solute concentration (decreased solute potential) and subsequent water movement into the apoplast. This, in turn, may reduce porosity and lead to increased fruit flesh translucency.
Abstract
The rate of postharvest softening of ‘McIntosh’ apples (Malus domestica Borkh.) was reduced by storage in a 1% O2 atmosphere at 1 or 3.5C. Apples stored in controlled atmosphere (CA) also maintained higher levels of the polyamines putrescine (PUT), spermidine (SPD), and spermine (SPN) in both skin and flesh tissues than those stored in air. The levels of putrescine and spermidine increased by 2- to 6-fold in CA-stored apples, while spermine decreased, but remained 2- to 5-fold higher than in air-stored fruit at both temperatures. Polyamines were also found to inhibit the in vitro activity of the cell wall-degrading enzyme polygalacturonase (PG). SPD and SPN were more effective than PUT, with SPN possessing the greatest inhibitory activity. These results are consistent with a hypothesis that increased polyamine levels are involved in the beneficial effects of CA storage and that polyamine activity could include the inhibition of cell wall degradation.
Abstract
Pectin methylesterase (PME, EC 3.1.1.11) was added to locular gel and pericarp of ripening tomato (Lycopersicon esculentum Mill.) and cell wall alterations were examined. Treatment of mature tomato locular gel with purified PME resulted in release of protoplasts. No protoplasts could be detected from immature locular gel or pericarp at any ripening stage examined under similar conditions. Net solubilization of pectins occurred with PME treatment in both tissues. Pectins solubilized with buffer or PME were of high molecular weight. Maximum protoplast release and pectin solubilization occurred at pH 5.0. Increased pectin solubilization in locular gel and pericarp is a result of polygalacturonase action on PME-induced deesterified pectin, the preferred substrate. Release of protoplasts from PME-treated mature locular gel suggests that maturation in this tissue involves alterations in cell wall structure that do not occur in pericarp.
Abstract
Fruit softening of apple (Malus domestica Borkh.) and the activity of β-galactosidase in 0.5 m citrate extracts of fruit cortex were compared for ‘Lodi’, ‘McIntosh’, ‘Golden Delicious’, and ‘York Imperial’ during storage at 0° or 3.3°, 10.0°, and 18.3°C. Enzyme activity per g fresh weight increased as fruits softened, but specific activity did not change. Cell wall galactose content also decreased during softening. The decrease in wall galactose was least in ‘Lodi’ which contained the lowest β-galactosidase activity. ‘York Imperial’ which softened most slowly showed the highest β-galactosidase activity at harvest and throughout storage. Concentrated enzyme preparations did not release measurable amounts of reducing sugar, uronic acid, or neutral hexose from isolated cell walls.
Abstract
A foliar spray of 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA) induced thickening and restricted elongation of strawberry (Fragaria × ananassa Duch.) petioles and stolon internodes. Leaf area of treated plants was lower than that of untreated plants. Stolon internodes of treated plants increased in cell size and number. Gibberellic acid (GA3) promoted leaf expansion and elongation of petioles and stolon internodes. A combination of PBA and GA3 induced less thickening and more elongation of petioles and stolon internodes and greater leaf area compared to treatment with PBA alone. There was a breakdown of cell walls of pith parenchyma in stolon internodes of untreated plants while the cell walls of PBA and GA3 treated plants remained intact.
Abstract
The outer stomatal openings on Citrus sinensis cv. Valencia fruit and leaves were formed by rupturing of the cuticle and possibly some of the outer epidermal cell wall. Small, 5µ diam, structures surrounded by wax were visible on the young fruit surface. The wax on immature fruit was soft, forming a continuous film with little surface structure. With maturation the progressive formation of more and harder epicuticular wax resulted in more visible structure. The eventual cracking and lifting of the wax film indicated loss of its ability to expand with the slow developing cuticle - cell wall complex. Leaves developed some surface wax structure but no platelet wax was formed. The leaves expanded rapidly and the leaf surface wax remained soft during this time.
Abstract
Abscission of maturing sweet cherry fruit (Prunus avium L. cv. Windsor) occurred at 2 different abscission zones, depending on the stage of fruit development. Immature fruit abscised at the upper zone between the pedicel and peduncle; mature fruit abscised at the lower zone between the fruit and receptacle. Separation in the abscission layer began directly above the stony pericarp and resulted in the formation of a cavity. Later separation occurred at the fruit : pedicel indentation and extended through the abscission layer toward the vascular bundles. Abscission involved the fracturing of cell walls as well as wall separation. There was no evidence of change in pectins, cellulose or other polysaccharides in the cell walls of the abscission layer prior to or during fruit separation. No starch accumulation in the abscission zone or lignification of tissue adjacent to the abscission layer was observed through fruit maturity.
Abstract
Single-node stem cuttings of Dieffenbachia amoena, Gentil were stored at 16 to 37° C and at 25 to 100% relative humidities. The cuttings required at least 2 days to produce suberin on cell walls near the cut surface, at least 6 days to form phellogen beneath suberized cells and at least 9 days to form a periderm layer. For periderm formation the optimum temperatures were 28 to 34 °C and optimum relative humidities 91 to 100%.
Abstract
Stone cells of highbush blueberry (Vaccinium corymbosum L.) were distributed primarily toward the periphery of the fruit; they apparently differentiated from ground parenchyma shortly after anthesis. Secondary cell wall material continued to be accreted through harvest, with lamellations about 1μm in width. The lignified walls were heavily pitted, with pits contiguous with those of adjacent stone cells. The number of stone cells may be correlated positively to the length of the growth season for each cultivar.