Andrew J. Macnish

Extension of the shelf life of banana fruit by 1-methylcyclopropene in combination with polyethylene bags

The effect of the new anti-ethylene compound 1-methylcyclopropene (1-MCP) in combination with polyethylene bags on the ripening of harvested banana fruit was investigated. 1-MCP treatment delayed peel colour change and fruit softening, and extended shelf life in association with suppression of respiration and C2H4 evolution. Banana fruit ripening was delayed when exposed to 0.01-1.0 mu l 1-MCP/l for 24 h, and increasing concentrations of 1-MCP were generally more effective for longer periods of time. Similar results were obtained with fruit sealed in polyethylene bags (0.03 mm thick) containing 1-MCP at various concentrations, but longer delays in ripening were achieved. The greatest longevity of about 58 days was realised by packing fruit in sealed polyethylene bags with 1-MCP at either of 0.5 or 1.0 mu l/l. Analyses of C2H4 and CO2 concentrations within polyethylene bags confirmed that 1-MCP suppressed both C2H4 evolution and respiration. Thus, application of 1-MCP in combination with the use of polyethylene bags can greatly extend the postharvest life of banana fruit

Responses of banana fruit to treatment with 1-methylcyclopropene

Experiments were conducted to determine levels of 1-methylcyclopropene (1-MCP) exposure needed to prevent ethylene-stimulated banana fruit ripening, characterise responses of ethylene-treated fruit to subsequent treatment with 1-MCP, and to test effects of subsequent ethylene treatment on 1-MCP-treated fruit softening. Fruit softening was measured at 20°C and 90% relative humidity. One hour exposure at 20°C to 1000 nl 1-MCP/l essentially eliminated ethylene-stimulated ripening effects. Exposure for 12 h at 20°C to just 50 nl 1-MCP/l was similarly effective. Fruit ripening initiated by ethylene treatment could also be delayed with subsequent 1-MCP treatment. However, 1-MCP treatment only slowed down ripening of ethylene-treated fruit when applied at 1 day after ethylene and was ineffective when applied 3 or 5 days after ethylene treatment. The ripening response of fruit treated with 1-MCP and subsequently treated with ethylene varied with interval time between 1-MCP and ethylene treatments. As time increased, the response of 1-MCP-treated fruit to ethylene was enhanced. Responses to 0.1, 1, 10 or 100 µl ethylene/l concentrations were similar. Enzyme kinetic analysis applied to 1-MCP effects on ethylene-induced softening of banana fruit suggested that 1-MCP inhibition is by noncompetitive antagonism of ethylene binding.

Effect of Abscisic Acid on Banana Fruit Ripening in Relation to the Role of Ethylene.

A bstractThe role of abscisic acid (ABA) in banana fruit ripening was examined with the ethylene binding inhibitor, 1-methylcyclopropene (1-MCP). ABA (0, 10−5, 10−4, or 10−3 mol/L) was applied by vacuum infiltration into fruit. 1-MCP (1 μL/L) was applied by injecting a measured volume of stock gas into sealed glass jars containing fruit. Fruit ripening, as judged by ethylene evolution and respiration associated with color change and softening, was accelerated by 10−4 or 10−3 mol/L ABA. ABA at 10−5 mol/L had no effect. The acceleration of ripening by ABA was greater at 10−3 mol/L than at 10−4 mol/L. ABA-induced acceleration of banana fruit ripening was not observed in 1-MCP treated fruit, especially when ABA was applied after exposure to 1-MCP. Thus, ABAs promotion of ripening in intact banana fruit is at least partially mediated by ethylene. Exposure of ABA-treated fruit to 0.1 μL/L ethylene for 24 h resulted in increased ethylene production and respiration, and associated skin color change and fruit softening. Control fruit (no ABA) was unresponsive to similar ethylene treatments. The data suggest that ABA facilitates initiation and progress in the sequence of ethylene-mediated ripening events, possibly by enhancing the sensitivity to ethylene.

A simple non-destructive method for laboratory evaluation of fruit firmness

Summary. Devices which offer simple, inexpensive, reliable and non-destructive objective measurement of fruit firmness assist in the monitoring of quality. For the present study, the Analogue CSIRO Tomato Firmness Meter (AFM), which measures fruit deformation under a 500 g load applied for 30 s was modified by replacing the analogue displacement gauge with a digital gauge and by using a laboratory jack for positioning the fruit in the vertical dimension. Non-destructive measurements of tomato fruit softening during ripening and determined with the Digital Firmness Meter (DFM) were strongly correlated with both firmness measured with the AFM (r2 = 0.96, n = 19) and with firmness determined subjectively by hand pressure (r2 = 0.93, n = 19). Similarly, mango fruit softening during ripening was monitored and DFM and hand firmness measurements were well correlated (r2 = 0.95, n = 10). The firmness of individual fruit could be measured around 20% faster with the DFM than with the AFM, and displacement was easier to read from the digital than from the analogue display. The DFM proved to be a suitable device for measuring fruit firmness in postharvest laboratory studies and warrants evaluation under commercial packing and handling conditions.

Softening response of banana fruit treated with 1-methylcyclopropene to high temperature exposure

Elevated temperatures experienced by harvested fruit can modulate theirripening. Moreover, heat treatments can be applied to reduce susceptibility tolow temperature disorders and to help control pests and diseases. Theethylene-binding inhibitor 1-methylcyclopropene (1-MCP) was used to investigatethe ethylene-mediated softening response of banana fruit exposed to elevatedtemperatures. A preliminary experiment was conducted to determine levels ofhightemperature (30–50 °C) imposed for a short periodof time that did not cause skin scald. The softening response of Williamsbananafruit treated with 1-MCP at various temperatures and durations wascharacterisedin subsequent experiments. Exposure of fruit to hot air for 60 minat 45 °C or for 30 min at50 °Ccaused 30–40% peel scald. The peel was not visibly damaged forfruit treated at 40 °C for up to 60 min.Softening of fruit treated with 1-MCP for 12 h at25 °Cand then held for 7 days at 30, 35 or 40 °C wasinhibited in proportion to increasing concentration over the range 0.01–1μl/l 1-MCP. However, softening was progressively enhanced withincreasing holding temperatures from 30–40 °Cand/or time from 1–7 days, although fruit treated with the higher 1-MCPconcentrations of 1 and 10 μl/l were comparatively lessresponsive to heat. Although banana fruit held at30–40 °Cdid not de-green, their increased softening at elevated temperatures andinhibition of this response by 1-MCP suggest that heat enhances synthesis ofnewethylene sites which mediated banana fruit softening.

Identification of intracellular calcium oxalate crystals in Chamelaucium uncinatum (Myrtaceae)

Intracellular inclusions in the pedicel and calyx-tube tissues of Chamelaucium uncinatum Schauer (Myrtaceae) flowers are irregular in shape. They were shown, by polarised light and scanning electron microscopy, to be birefringent 8.9–29.5 μm druse (i.e. aggregate) crystals. Energy-dispersive X-ray spectroscopy showed that these crystals were predominantly composed of calcium. Histochemical and acid-solubility tests indicated that the crystals were calcium oxalate. Raman microprobe spectroscopy was used to confirm this chemical identity. The calcium oxalate crystals were located in xylem-vessel lumens and also in parenchyma cells adjacent to vascular tissues. Thus, the crystals may function to regulate soluble calcium concentrations in C. uncinatum tissues near sites where calcium is unloaded from the xylem.

Involvement of ethylene in postharvest senescence of Boronia heterophylla flowers

Treatment of cut flowering Boronia heterophylla (red boronia) stems with 10 mu L ethylene/L for 72 h at 20 degrees C induced flower senescence and abscission, and thereby reduced stem fresh weight and vase life. Pretreatment with 1-methylcyclopropene (1-MCP) reduced these ethylene effects. Treatment of B. heterophylla with 10 mu L ethylene/l for a shorter 12 h period at 20 degrees C did not affect vase life. Rates of endogenous ethylene production by B. heterophylla flowers increased in association with wilting during flower senescence.

Transcriptomic analysis reveals numerous diverse protein kinases and transcription factors involved in desiccation tolerance in the resurrection plant Myrothamnus flabellifolia

The woody resurrection plant Myrothamnus flabellifolia has remarkable tolerance to desiccation. Pyro-sequencing technology permitted us to analyze the transcriptome of M. flabellifolia during both dehydration and rehydration. We identified a total of 8287 and 8542 differentially transcribed genes during dehydration and rehydration treatments respectively. Approximately 295 transcription factors (TFs) and 484 protein kinases (PKs) were up- or down-regulated in response to desiccation stress. Among these, the transcript levels of 53 TFs and 91 PKs increased rapidly and peaked early during dehydration. These regulators transduce signal cascades of molecular pathways, including the up-regulation of ABA-dependent and independent drought stress pathways and the activation of protective mechanisms for coping with oxidative damage. Antioxidant systems are up-regulated, and the photosynthetic system is modified to reduce ROS generation. Secondary metabolism may participate in the desiccation tolerance of M. flabellifolia as indicated by increases in transcript abundance of genes involved in isopentenyl diphosphate biosynthesis. Up-regulation of genes encoding late embryogenesis abundant proteins and sucrose phosphate synthase is also associated with increased tolerance to desiccation. During rehydration, the transcriptome is also enriched in transcripts of genes encoding TFs and PKs, as well as genes involved in photosynthesis, and protein synthesis. The data reported here contribute comprehensive insights into the molecular mechanisms of desiccation tolerance in M. flabellifolia.

Effects of short-term N2 treatments on ripening of banana fruit

Summary Experiments were conducted to evaluate the effects of anoxia treatments on banana fruit ripening. Pre-climacteric banana fruit were exposed to pure N2 for 0, 6, 9, 12 or 24 h, then stored for up to 3 weeks at 20°C and approx. 90% relative humidity. Changes in peel colour, fruit firmness and post-harvest life were evaluated. Ripening was inhibited most effectively in fruit exposed to N2 for 9 h. Furthermore, exposure of banana fruit to pure N2 gas for 9 h reduced the rates of ethylene production and respiration, as well as the activities of polygalacturonase and pectin methyl esterase. These results suggest that anoxia treatment is a feasible technology to inhibit ripening and extend the shelf-life of banana fruit.

Anatomy of ethylene-induced floral-organ abscission in Chamelaucium uncinatum (Myrtaceae)

Postharvest abscission of Geraldton waxflower (Chamelaucium uncinatum Schauer) flower buds and flowers is ethylene-mediated. Exposure of floral organs to exogenous ethylene (1 mu L L-1) for 6 h at 20 degrees C induced separation at a morphologically and anatomically distinct abscission zone between the pedicel and. oral tube. Flower buds with opening petals and flowers with a nectiferous hypanthium were generally more responsive to exogenous ethylene than were flower buds enclosed in shiny bracteoles and aged (senescing) flowers. The anatomy of abscission-zone cells did not change at sequential stages of floral development from immature buds to aged flowers. The zone comprised a layer of small, laterally elongated-to-rounded, closely packed and highly protoplasmic parenchyma cells. Abscission occurred at a two- to four-cell-wide separation layer within the abscission zone. The process involved degradation of the middle lamella between separation layer cells. Following abscission, cells on both the proximal and distal faces of the separation layer became spherical, loosely packed and contained degenerating protoplasm. Central vascular tissues within the surrounding band of separation layer cells became torn and fractured. For flower buds, bracteoles that enclose the immature floral tube also separated at an abscission zone. However, this secondary abscission zone appeared less sensitive to ethylene than the primary ( central). oral-tube abscission zone as bracteoles generally only completely abscised when exposed to 10 mu L L-1 ethylene for the longer period of 24 h at 20 degrees C. The smooth surfaces of abscised separation-layer cells suggest that hydrolase enzymes degrade the middle lamella between adjacent cell walls.