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Petiole protoplasts of the sweetpotato [Ipomoea batatas (L.) Lam.] cultivars Red Jewel and Georgia Jet formed cell walls within 24 hours and divided in 2 to 3 days. Pretreating enzyme solutions with activated charcoal increased the viability and division frequency of protoplasts. Culture of protoplast-donor plants in a medium containing STS did not affect plant growth, protoplasm yield, or viability, but did increase the division frequency. Culture of protoplasts for 24 hours in a medium containing DB, a cell wall synthesis inhibitor, or staining of protoplasts with FDA did not significantly affect division frequency. The division frequency of protoplasts cultured in liquid medium was significantly higher than that of protoplasts cultured in agarose-solidified medium. Cell cycle analysis of petioles and freshly isolated protoplasts showed that the latter has a significantly higher proportion of nuclei in G1 phase. Protoplasts did not initiate DNA synthesis or mitosis within the first 24 hours of culture. Low-frequency regeneration of shoots from protoplast-derived callus was accomplished on MS medium containing 1.0 mg ldnetin/liter when preceded by MS medium modified to contain only (in mg·liter-1) 800 NH4NO3, 1400 KNO3, 0.5 2,4-D, 0.5 kinetin, and 1.0 ABA. Roots produced from protoplast-derived callus formed adventitious shoots after 4 weeks on MS medium containing 2% sucrose, 0.02 mg kinetin/liter and 0.2% Gelrite. Secondary shoot formation from regenerated roots will be a more effective means of obtaining plants from protoplasts than direct shoot regeneration from callus. Chemical names used: silver thiosulfate (STS): 2.6-dichlorobenzonitrile (DB); fluorescein diacetate (FDA): 2.4-diacetate (FDA); 2.4 dichlorophenoxyacetic acid (2,4-D); abscisic acid (ABA).
Tissue firmness of ripe tomatoes is controlled by cell wall integrity of the fruit tissue and by the enzymatic softening that normally occurs during ripening. This study was conducted to determine the physical characteristics of cells and tissues of mature green (MG) and ripe fruit that might account for differences in firmness between `Rutgers' (normal), `Flora-Dade' (Firm), and two mutant lines called high-pigment (T4065 hp) and dark-green (T4099 dg), both of which possess extra firm fruit. Fruit samples were tested for resistance to a force applied to whole fruit and to sections of the pericarp tissue and by stress-relaxation analysis. Determinations were also made of cell density and cell wall content within the pericarp tissue. Fruit of mutant lines had firmer tissue than either `Rutgers' or `Flora-Dade' at MG or ripe. Whole fruit compression measurements showed that T4099 dg was firmer than T4065 hp or `Rutgers' at MG and firmer than `Flora-Dade' and `Rutgers' when ripe. Whole fruit of `Flora-Dade' were significantly firmer than `Rutgers' at MG and ripe. Firmness measured by compressive strength also showed that mutant lines had firmer pericarp tissue than the wild types at both MG and ripe stages. Stress-relaxation analysis showed that MG fruit of T4099 dg had greater tissue elasticity than `Rutgers' or `Flora-Dade'. Ripe fruit of both mutant lines had more tissue elasticity than wild types. There were no apparent differences among the genotypes due to tissue relaxation. From these analyses, tissue elasticity appears to be a significant parameter in determining tissue firmness in the tomato genotypes used in this study. Firmness and textural quality of ripe tomatoes appeared to be dependent on elasticity of the pericarp tissue and on the level of enzymatic softening during ripening.
Excision of the flower from the peach [Prunus persica (L.) Batsch.] flower bud raised the 50% injury temperature of flowers (cooled at 1C/hour) from -18 and -20C to -10 and -13C on two test dates, 26 Feb. 1988 and 5 Dec. 1990, respectively. Ice inoculation of the excised flowers at -3C further raised the 50% injury temperature to -7 and -8C for the two dates, respectively. These observations suggest that supercooling is a true mechanism for avoiding freezing injury. Low temperature scanning electron microscopy of freeze fractured cells verified that the flower froze intracellularly, whereas the subtending tissue froze extracellularly. Ice inoculation of the flower and the flower bud axis from which the scales were removed demonstrated that a barrier to ice propagation (effective to -11C) from the flower bud axis to the flower was present. This barrier may involve the provascular strands and a cell zone at the flower base (BZ) that were devoid of intercellular spaces. These tissues also had smaller cells, smaller vacuoles, greater ratio of cell wall thickness to cell size than tissue just below the BZ, which may result in greater cell rigidity and restriction of extracellular freezing. The cells outside the provascular strands at the base of the flower were also lacking in intercellular space, were smaller in size, and had a higher ratio of cell wall thickness to cell size compared to cells near the base of the scales. In the intact flower buds in which the flowers supercool below -11C, the presence of the first and second scales was important to full expression of supercooling because their removal raised the supercooling point, whereas the removal of lower scales did not. Sequestration of ice by the first two subtending scales during the early stages of freezing may be important to the creation of a dry region at the flower base that prevents ice propagation into the flower at temperatures below -11C.
Abstract
The wound-healing process in cuttings of Pelargonium X hortorum L.H. Bailey cv. Yours Truly was studied using histological and histochemical techniques. Anatomical changes at the wounded surface of cuttings within 24 hours included deposition of a granular, amber-colored substance identified as suberin on the cell walls, in the intercellular spaces, and in the lumina of xylem vessels. Wound xylem, adventitious root primordia, and wound callus developed within 7 days. A periderm developed 14 to 21 days after wounding and its cell walls were suberized.
Abstract
Tannin cells from fruit of Japanese persimmon (Diospyros kaki L.) cvs. Fuyu [pollination-constant and nonastringent (PCNA)], Chokenji [pollination-variant and nonastringent (PVNA)], Hiratanenashi [pollination-variant and astringent (PVA)], and Kuramitsu [pollination-constant and astringent (PCA)], were observed by florescence microscope (FM) and scanning electron microscope (SEM) on 4 July, when all cultivars were very astringent, and on 5 Sept., when ‘Fuyu’ and ‘Chokenji’ fruit had completely lost their astringency. ‘Hiratanenashi’ and ‘Kuramitsu’ fruit, however, were still quite astringent on the latter date. FM observations on 4 July indicated that tannin cells of all fruit possessed some discontinuous portions in the cell walls. SEM observations of fractured surfaces of fruit flesh verified the existence of pores in the tannin cell walls. Moreover, coagulated internal contents of tannin cells (caused by the fixatives) had protruded through the pores. On 5 Sept., however, the pores in tannin cell walls of ‘Fuyu’ and ‘Chokenji’ were not present, and the surface of coagulated internal contents had become smooth. ‘Hiratanenashi’ and ‘Kuramitsu’ fruit on 5 Sept. showed little change in the structure from that observed on 4 July. Pore occlusion occurred in ‘Hiratanenashi’ fruit that were treated on the tree with ethanol fumes to remove astringency, which indicates that loss of astringency induces structural changes in tannin cell walls.
Abstract
The external surfaces and internal structures of particles of milled pine bark (Pinus taeda L. and P. elliottii Engelm.) were examined with scanning electron microscopy. Numerous external openings, cracked cell walls and internal cellular connections, that might allow water penetration were observed. Periderm surfaces were without pores, and contained rough surfaces and apparently waxy substances that might resist water penetration or absorption.
, swelling of the cell walls was quantified by determining cell wall thickness using image analysis (Cell-P, Olympus Europa). The osmolarity of incubation media and of juice extracted from the same fruit as that used in the plasmolysis and cell wall swelling
`Golden Delicious' apples (Malus domestics Borkh.) were treated with heat or CaCl2 solutions or a combination thereof to determine the effects of these treatments on decay and quality of fruit in storage. Heat treatment at 38C for 4 days, pressure infiltration with 2% or 4% solutions of CaCl2, or a combination of both, with heat following CaCl2 treatment affected decay and firmness during 6 months of storage at 0C. The heat treatment alone reduced decay caused by Botrytis cinerea (Pers.:Fr.) by ≈30%, while heat in combination with a 2% CaC12 solution reduced decay by ≈60 %. Calcium chloride solutions of 2% or 4% alone reduced decay by 40 % and 60 %, respectively. Heat treatments, either alone or in combination with CaC12 treatments, maintained firmness (80 N) best, followed by fruit infiltrated with 2% or 4% solutions of CaCl2 alone (70 N) and the nontreated controls (66 N). Instron Magness-Taylor and Instron compression test curves show that heat-treated fruit differed qualitatively and quantitatively from nonheated fruit. Heat treatment did not increase the amount of infiltrated Ca bound to the cell wall significantly, and a combination of heat treatment after CaCl2 infiltration increased surface injury over those fruit heated or infiltrated with CaCl2 solutions alone.
Bronzing of strawberry (Fragaria ×ananassa Duchesne) fruit that is not the result of arthropod feeding or chemical spray application occurs frequently in California's central coast strawberry production region from late spring through midsummer, a period characterized by relatively high temperature, low relative humidity, and high solar irradiance. The cause of this phenomenon is not known, but in preliminary trials, intermittent, midday misting of plants and increased drip irrigation rate resulted in reduced incidence of fruit bronzing. To characterize the bronzing phenomenon and its development in strawberry fruit tissues, we conducted an anatomical and histochemical examination of bronzed fruit. Bronzed and nonbronzed fruit were sampled over a range of fruit maturities. Results show that bronzing derives from a lesion at the cortical surface early in the fruit's development. Epidermal cells become radially compressed and the cell contents coalesce into a densely staining mass. The cuticular layer becomes disrupted and discontinuous. As the fruit develops, densely staining materials, possibly phenolic precipitates, accumulate within subepidermal cells of bronzed fruit, subepidermal cell walls thicken, and intercellular spaces fill with pectic substances and other densely staining materials. Results are consistent with reports of sunscald injury from other fruit species, and raise the possibility that strawberry bronzing occurs in response to heat or solar radiation injury.
Effects of short-term exposure to a 15% CO2 atmosphere on nectarines [Prunus persica (L.) Batsch (Nectarine Group) `Summer Red'] inoculated with Monilinia fructicola (Wint.) Honey (causal agent of brown rot) were investigated. Nectarines were inoculated with spores of M. fructicola and incubated at 20 °C for 24, 48 or 72 hours and then transferred to storage in either air or air enriched with 15% CO2 at 5 °C. Fruit were removed from storage after 5 and 16 days and were examined for brown rot decay immediately and after ripening in air for 3 days at 20 °C. Noninoculated nectarines were stored and treated likewise for evaluation of postharvest fruit attributes to determine their tolerance to 15% CO2. Incubation period after inoculation, storage duration, and storage atmosphere had highly significant effects on fruit decay. `Summer Red' nectarines tolerated a 15% CO2 atmosphere for 16 days at 5 °C. Development of brown rot decay in fruit inoculated 24 hours before 5 or 16 days storage in 15% CO2 at 5 °C was arrested. After 3 days ripening in air at 20 °C, the progression of brown rot disease was rapid in all inoculated nectarines, demonstrating the fungistatic effect of 15% CO2. The quantity of fungal cell wall materials (estimated by glucosamine concentration) was compared to visual estimation of decayed area and visual rating of fungal sporulation. The glucosamine assay defined the onset and progress of brown rot infection more precisely than either of the two visual tests.