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- Author or Editor: Jacqueline Burns x
Oxygen uptake and glycosidase activities were examined in normal and granulated juice vesicles of several citrus fruit. Oxygen uptake was low in normal juice vesicles isolated from freshly harvested `Lee' tangelos [Citrus reticulate Blanco cv. Clementine × (Citrus paradisi Macf. cv. Duncan × Citrus reticulate Blanco cv. Dancy)] and stored `Dancy' tangerine (C. reticulate Blanco) and `Marsh' grapefruit (Citrus paradisi Macf.) (35.7, 17.9, and 11.6 μl O2/hr per g fresh weight, respectively), but was 2- to 3-fold higher in granulated juice vesicles. As severity of granulation increased in grape. fruit, O2 uptake increased. Oxygen uptake in normal and disordered juice vesicles of all citrus fruit examined was reduced to nondetectable levels with 0.1 mM KCN and was insensitive to salicylhydroxamic acid. α - and β -galactosidase and α- and β -glucosidase activities were present in extracts of normal grapefruit juice vesicles (123, 214, 51, and 25 nmol·hr-1·g-1 fresh weight, respectively) and was 2- to 3-fold higher in extracts of granulated tissue. α- and β -mannosidase activities, nondetectable in normal juice vesicle extracts, were present in extracts from granulated tissue. The results suggest that increased metabolic activity occurs in granulated juice vesicles and the energy produced may be used to support cell wall synthesis and modification. Increases in O2 uptake and glycosidase activities correlate well with observed symptoms of section-drying in citrus.
1-Methylcyclopropene (1-MCP) is a gaseous ethylene-binding inhibitor used to control or delay ethylene-related postharvest effects in a range of horticultural commodities. The potential for preharvest applications of 1-MCP to prevent unwanted defoliation using ethephon to loosen mature citrus fruit is presented. Although there was no difference in mature fruit loosening by ethephon + 1-MCP treatments, 1-MCP reduced defoliation caused by ethephon. The gaseous nature of 1-MCP is an impediment to uniform application and consistent efficacy. A sprayable 1-MCP formulation would be of great value for preharvest use in many horticultural crops.
To successfully use abscission agents for ‘Valencia’ sweet orange mechanical harvesting throughout the harvest season, unwanted flower, fruitlet, and leaf drop must be assessed and minimized. Ethephon (400 mg·L−1), 1-methylcyclopropene (1-MCP; 5 mm), ethephon + 1-MCP, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP; 200 mg·L−1), and a kinetic adjuvant control [0.15% (v/v)] were applied to ‘Valencia’ branches at various times from full bloom in Mar. 2006 to the end of full bloom in Mar. 2008. Effects of these treatments on fruit detachment force (FDF) and abscission of developing and mature fruit, flowers, and leaves were recorded. Three separate response periods to abscission agent applications were observed: the first spanned the first 100 days after bloom (DAB) and was characterized by high initial response followed by decreasing sensitivity; the second spanned between 100 and 225 DAB and was characterized by little to no response; and the third spanned from 225 DAB to harvest and was characterized by a gain in sensitivity. Young fruitlets in the first response period were highly sensitive to ethephon but were less sensitive to CMNP or ethephon + 1-MCP. Mature fruit in the third response period were highly sensitive to CMNP and less sensitive to ethephon or ethephon + 1-MCP. The application of ethephon resulted in high leaf abscission and showed no clear sensitivity pattern throughout both cropping years. CMNP or ethephon + 1-MCP application caused minimal leaf abscission. The same abscission agent treatments were applied on whole tree canopies 6 and 28 DAB in Mar. 2007. Application date had no significant effect on the measured parameters. Although ethephon application induced high initial leaf drop, leaf area indices determined 7 months after any compound application were not significantly different. However, subsequent 2008 yield in trees sprayed with ethephon in 2007 was significantly less, whereas 2008 flower number was higher. The results indicate a complex interaction of fruitlet abscission and leaf loss during the first response period contributed to yield reduction and increased flower number in ethephon-treated trees.
Plant growth regulators (PGRs) play important roles in the way plants grow and develop. Myriad processes important to horticultural crops are regulated by PGRs. Changes in the presence, balance, and distribution of PGRs communicate developmental, stress-related, or environmental cues that alter growth. Short-distance communication involves changes in biosynthesis or metabolic conversion, whereas longer-distance communication may also require export and translocation of PGRs, their precursors or metabolites. Examples are presented that demonstrate PGR communication between roots and shoots in horticultural commodities. For example, increased duration and intensity of flooding stress can result in synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC), precursor of the PGR ethylene, in roots. ACC transported to the shoot through the transpiration stream is converted to ethylene and causes leaf epinasty. Roots sense the onset of water stress and can communicate the need to close leaf stomata by altering abscisic acid (ABA) levels in the shoot. Daylength and temperature regulate synthesis and transport of gibberellins, which promote stem elongation and stolon formation and inhibit tuberization in potato. Outgrowth of axillary buds following the decapitation of the apical meristem is dependent on synthesis and transport of cytokinin from root to the axillary buds as well as the balance of indole-3-acetic acid (IAA) cytokinin, and additional messengers. Current research in the field of long-distance communication within plants is uncovering novel messengers and altering our view of the central roles for PGRs in such signaling.
The effect of temperature on the ability of 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) and ethephon to induce ethylene evolution and abscission of mature fruit and leaves was determined using 3-year-old potted `Hamlin' orange [Citrus sinensis (L.) Osb.] trees in environment-controlled growth rooms in seasons 2001-02 and 2002-03. Ethylene evolution and abscission of CMNP or ethephon-treated fruit and ethephon-treated leaves were highly temperature dependent. Fruit detachment force (FDF) and fruit ethylene evolution were not affected by application of ethephon at 200 mg·L-1 or CMNP at 200 mg·L-1 when air temperature was 10 °C for ethephon treatment or ≤15.6 °C for CMNP treatment. However, ethylene evolution of CMNP or ethephon-treated fruit increased sharply, and FDF decreased drastically as temperature increased from 10 to 26.7 °C for ethephon treatment or from 15.6 to 26.7 °C for CMNP treatment. Several 10 hour day/14 hour night temperature regimes were explored to determine the effect of varying daily and nightly temperatures on efficacy and ethylene evolution. At least 3 days of exposure to 21/10 °C were required for CMNP to effectively loosen fruit, whereas only one day of exposure to 26.7/15.6 °C was enough to induce similar changes. At 21/10 °C, CMNP significantly reduced FDF to<25 N and markedly enhanced fruit ethylene evolution, regardless of interruption by 1 day of low temperature at 10/10 °C in the first 5 d after application. Ethephon had no significant effect on leaf ethylene evolution and leaf abscission when temperature was 10 °C, but caused a marked increase in both leaf ethylene evolution and leaf abscission as temperature increased from 10 to 26.7 °C. CMNP did not stimulate leaf ethylene evolution and leaf abscission regardless of temperature. Chemical names used: 5-chloro-3-methyl-4-nitro-1 H-Pyrazole (CMNP); 2-chloroethylphosphonic acid (ethephon).
Pectin methylesterase (PME, EC 184.108.40.206) 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.
Normal and collapsed juice vesicles were removed from stored late-harvested grapefruit segments (Citrus paradisi Macf. cv. Marsh) and the cell wall anatomy of epidermal and internal parenchyma was compared with light, scanning electron, and transmission electron microscopy. Normal juice vesicles were turgid and elongate, and epidermal cells and internal parenchyma were intact. Collapsed juice vesicles appeared flattened, and internal parenchyma were compressed. Cell wall thickening occurred in internal parenchyma and single or clustered epidermal cells of collapsed vesicles. Cell walls of the same cells in normal vesicles were thin. Epidermal and internal parenchyma cell walls of collapsed vesicles were 10 to 50 to 10 to 20 times the thickness, respectively, of corresponding normal cell walls. Lignin was detected in thickened cell walls of epidermal and internal parenchyma of collapsed vesicles. The results suggest that cell wall synthesis in vesicles is a symptom of section drying in grapefruit.
Ca2+ content in cell wall-middle lamella (CW–ML) areas of outer and inner pericarp, placenta, and gel parenchyma of ripening tomato (Lycopersicon esculentum Mill. cvs. Celebrity and Jumbo) and mesocarp of ripening peach [Prunus persica (L.) Batsch cv. Georgia Belle] was determined by energy dispersive (EDS) X-ray microanalysis. Ca2+ increased from 1.50 to 6.95 mg·g–1 dry weight in CW–ML of outer pericarp and 0.98 to 2.60 mg·g–1 dry weight in CW–ML of inner pericarp during ripening. Ca2+ content remained constant in tomato placenta and peach mesocarp, and was undetectable in tomato gel parenchyma throughout ripening. CW–ML of peach mesocarp had lower Ca2+ content than tomato pericarp and placenta at all ripening stages, but total peach uronic acid content was 2.5 times greater. Pectin methylesterase (PME) activity increased in tomato pericarp as fruit ripened, but remained low and unchanged in placenta and gel parenchyma. PME treatment of pericarp increased amounts of CW–ML Ca2+ in the breaker stage but not in the green mature stage. The results indicate that increased amounts of Ca2+ are bound to CW–ML of tomato pericarp as ripening occurs but not in placenta or peach mesocarp. Pectin deesterification and wall softening during ripening may in part be factors that control the presence and amount of CW–ML Ca2+.