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Abstract
Following the application of 2-chloroethyl-tris-(2-methoxyethoxy)-silane (CGA 13586), an ethylenereleasing compound, to olive (Olea europaea L.) shoots, 2 abscission zones were observed. One occurred at the proximal, the other at the distal end of the pedicel. Actual separation occurred mostly at the distal end of the pedicel. Changes observed during the development of the abscission zone included: cell plasmolysis, cell wall and middle lamella dissolution, starch grain accumulation and a general breakdown of cells at the abscission zone.
Abstract
Fungal cell-wall lysing enzymes have been shown to induce ethylene production in different plant systems. The effect of endogenous plant cell-wall lysing enzymes on ethylene synthesis in fruit has received only limited attention. Therefore, tomato fruit (Lycopersicon esculentum, Mill.) were vacuum–infiltrated with the tomato cell-wall enzymes, polygalacturonase I and II (PG I, PG II) and pectinmethylesterase (PME). Fruit ethylene levels were observed to increase relative to either salt, buffer, or boiled enzyme controls. This increase in ethylene production occurred in green ‘Cherry’ tomato fruit as well as in the mutants rin, nor, and Cornell 111. Enzyme-induced ethylene synthesis generally peaked at or before 17 to 20 hr and decreased to lower or basal levels in most immature normal cultivars by 42 hr after treatment. Ethylene was maintained at high levels, however, in some (possibly more mature) green fruit, as well as in all mutant lines. PG II was more effective than PG I in inducing ethylene production and PME seemed to enhance the ethylene-inducing activity of PG II.
Abstract
Hemicelluloses and polyuronides from the cell wall of ripening tomato (Lycopersicon esculentum Mill. cv. Rutgers) fruit were examined using gel-filtration chromatography. Gel filtration of polyuronides revealed that these polymers were extensively degraded during ripening, as evidenced by the increase in the quantity of polymers that fractionated on the gel. Low molecular weight polyuronides were first evident in fruit harvested at the turning stage and they constituted the major portion of the polyuronides obtained from fruit at more advanced stages of ripening. The appearance of degraded polyuronides corresponded well with the activity of endo-D-galacturonanase, which appeared to be solely responsible for the degradation of these wall polymers. The cell wall hemicelluloses were also affected during ripening; gel-filtration analyses revealed marked changes in the molecular-weight distribution of these polymers. Hemicelluloses from immature green and mature green fruit were similar chromatographically, whereas those from fruit harvested during ripening showed progressively lower quantities of high molecular weight polymers and higher quantities of low molecular weight polymers (<40,000). These changes coincided with the degradation of the pectic polysaccharides; however, in vitro studies using isolated cell wall showed that pectin degradation occurred independently of the changes in hemicelluloses.
Abstract
Cut roses (Rosa hybrida L. cv. White Butterfly) pulsed with 14C-sucrose were analyzed for changes in total and labeled sucrose, glucose, fructose and starch after chases of various periods in either water or sucrose solution. Changes of 14C in an ethanol-insoluble fraction defined as the “cell wall fraction” were also studied. Changes in total amounts of each sugar did not correspond to changes in their respective labeled sugars, and these dissimilariteis in pattern indicated rapid turnover of each sugar in stems, and moderate turnover in leaves, with a general movement of 14C out of both leaves and stems. In flower heads, there was an initially short, overall incorporation of labeled sugars, followed by a gradual increase of 14C-glucose and 14C-fructose, but not 14C-sucrose. Starch turnover was appreciable in flower heads and in leaves, but not in stems. The leaves of roses held in the water chase showed the greatest turnover of starch. Incorporation of 14C into that portion of the ethanol-insoluble fraction designated “cell wall fraction” was greater in flower heads of roses chased in sucrose than those chased in water, but the type of chase solution used had little effect on incorporation of 14C into the “cell wall fraction” of leaf and stem tissue.
Frequency and distribution of microcracks in the cuticular membrane (CM) were monitored in cheek, suture, pedicel cavity and stylar regions of developing sweet cherry (Prunus avium L.) fruit using fluorescence microscopy following infiltration with a fluorescence tracer (1 to 2 min in 0.1% w/v acridine orange containing 50 mm citric acid and 0.1% Silwet L-77, pH 6.5). These microcracks were limited to the cuticle, did not extend into the pericarp and were only detected by microscopy. Fruit mass and surface area increased in a sigmoidal pattern with time between 16 days after full bloom (DAFB) and maturity. The increase in frequency of fruit with microcracks paralleled the increase in fruit mass. During early development (up to 43 DAFB) the CM of `Sam' fruit remained intact. However, by 57 DAFB essentially all `Sam' fruit had microcracks in the pedicel cavity and ≈25% in the suture region with little change thereafter. At maturity percentage of `Sam' fruit with microcracks in cheek, suture, pedicel cavity and stylar end region averaged 23%, 25%, 100%, and 63%, respectively. Similar data were obtained for `Hedelfinger' (70% and 100% for cheek and pedicel cavity, respectively), `Kordia' (80% and 100%) and `Van' (100% and 100%). Generally, microcracks were most severe in pedicel cavity and stylar end region. Most of the first detectable microcracks formed above periclinal walls of epidermal cells perpendicular to their longest axis (72% and 92% in cheek and stylar regions, respectively). The other microcracks formed above the anticlinal walls were mostly oriented in the direction of the underlying cell wall. There was no difference in projected surface area, length/width ratio or orientation among epidermal cells below, adjacent to or distant from the first detectable microcracks in the CM. However, as length of microcracks increased the projected surface area of cells underlying cracks increased suggesting strain induced upon cracking of the CM. Permeability of excised exocarp segments in osmotic water uptake was positively correlated with number of stomata and number of microcracks in the CM. From our results we suggest that strain of the epidermal system during stage III of fruit growth is a factor in “microcracking” of the CM that may predispose fruit to subsequent rain-induced cracking.
Some plant-derived natural volatile compounds exhibit antifungal properties and may offer an opportunity to control the causes of postharvest spoilage without affecting quality of, or leaving a residue on, fresh produce. The natural wound volatile (E)-2-hexenal has exhibited significant antifungal activity in earlier studies, but effects on spore germination and mycelial growth have not been separated, nor has the inhibitory mode of action been determined. To determine the efficacy of (E)-2-hexenal for control of Botrytis cinerea Pers. ex Fr. spore germination and mycelial growth, and to examine the mode of action, in vitro and in vivo studies were performed. Under in vitro bioassay conditions, spore germination was more sensitive to the compound than was mycelial growth. Vapor from 10.3 μmol of (E)-2-hexenal in a 120-mL petri dish completely inhibited spore germination. However, 85.6 μmol of (E)-2-hexenal was required to completely inhibit mycelial growth. Lower concentrations of the compound (5.4 and 10.3 μmol) significantly stimulated mycelial growth, especially when the volatile was added 2 days following inoculation. Mycelial growth did not occur as long as the vapor-phase concentration was 0.48 μmol·L-1 or greater. Light microscopy analysis indicated that a high concentration of volatile compound dehydrated fungal hyphae and disrupted their cell walls and membranes. Exposure of B. cinerea-inoculated and non-inoculated strawberry (Fragaria ×ananassa Duch.) fruit in 1.1-L low-density polyethylene film-wrapped containers to vapor of (E)-2-hexenal at 85.6 or 856 μmol (10 or 100 mL, respectively) per container for durations of 1, 4, or 7 days during 7 days of storage at 2 °C promoted the incidence of B. cinerea during subsequent shelf storage at 20 to 22 °C. Loss of fruit fresh mass and fruit firmness during storage at 22 °C was increased by (E)-2-hexenal treatment, but fruit total soluble solids, pH, titratable acidity, and color (L, C, and H values) were not affected. Thus, maintenance of a high vapor-phasel level of (E)-hexenal, perhaps >0.48 μmol·L-1, may be necessary to inhibit mycelial growth and avoid enhancing postharvest mold problems, while significantly higher levels may be necessary to completely eliminate the pathogen.
intercellular spaces were seen between MMCs ( Fig. 1B ). Histochemical staining and examination showed that cell walls and starch grains were red. A large and conspicuous nucleus was located in the center of the MMCs. A few large black lipid droplets were
Abstract
The influence of stomata, the stylar scar, cuticular fractures, and Ca2+ on susceptibility of ‘Bing’ sweet cherry fruit (Prunus avium L.) to water injury was studied. Water injury was first detected as an increase in cell turgor. Water penetration caused separation of the cuticle from the epidermal cell wall. Swelling in the epidermal cell wall region resulted in cuticular fracturing that generally preceded fruit cracking. Uncracked fruit that had cuticular fractures softened rapidly. Stomata were sparsely distributed on the fruit surface and were often fixed in an open or partially open position. Water injury was not visible at stomata even when injury occurred adjacent to the stomatal region. Initial signs of injury were commonly visible near the stylar scar. Histochemical studies revealed that the surface of the stylar scar was devoid of a cuticle covering and was rich in insoluble carbohydrates. Greater penetration of solute containing 45Ca2+ occurred at the stylar scar. Fine fractures in the cuticle surface were observed in fruit at harvest time in 1985 and 1986. Cherry fruit with cuticular fractures had a higher water absorption rate than unfractured fruit. In immersion tests, Ca2+ reduced cherry cracking. EGTA increased fruit cracking; this increase was negated by adding Ca2+. Neither Ca2+ nor EGTA affected the water absorption rate of the fruit. EGTA decreased the cracking threshold of the fruit, while Ca2+ increased it. Soluble pectin content of the immersion solution rose with increasing incubation times. EGTA increased while Ca2+ markedly decreased soluble pectin concentration in the immersion solution. Histochemical studies indicated a breakdown of the cell wall structure in the epidermal region of water-injured fruit. Autoradiographs of fruit immersed in a solution containing 45Ca2+ showed the epidermal region to be the site of Ca2+ action in altering fruit cracking. Chemical name used: Ethyleneglycol-bis-(β-aminoethyl ether) N,N,N,N-tetraacetic acid (EGTA)
Abstract
The effect of imbibition and drying rates on colyledon cracking in snap beans, Phaseolus vulgaris L., was studied. Six snap bean cultivars, representing various degrees of susceptibility to cotyledon cracking, were compared. Data indicated that differences in the rate of imbibition and drying were not responsible for differences in susceptibility to cotyledon cracking. The crack-resistant ‘Improved Higrade’ and moderately-resistant ‘Earliwax’ imbibed water faster than the crack-susceptible cultivars. Anatomical studies indicated that cracking was more frequent across the cell walls of the cotyledon cells than along the middle lamellae in all cultivars.
Abstract
Protoplasts were isolated from actively growing callus and cell suspension cultures initiated from apple leaf discs. Callus and cell suspension cultures incubated in a solution of 0.7 m mannitol, 0.01 m CaCl2, 2% cellulysin, 0.5% macerase yielded protoplasts from about 75% of the callus cells and 90% of the suspension cells. Protoplast viability was 95–98% upon isolation, and 80–85% after a 2-week culture in a modified Murashige and Skoog (MS) medium. About 60% of the protoplasts regenerated cell walls, and 5–10% of the original protoplasts exhibited cell division.