Changes in activities of cell wall hydrolases during ethylene-induced ripening in banana: effect of 1-MCP,ABA and IAA

Softening during ripening in climacteric fruit is generally attributed to degradation in cell wall assembly, particularly the solublization of pectin. These changes could involve increased activities of various cell wall hydrolases. Their activity is believed to be regulated by ripening-related hormones and/or other signal molecules. Activities of pectin methyl esterase (PME), polygalacturonase (PG), pectate lyase (PL) and cellulase in banana cv. dwarf cavendish fruit were measured over a period of 7 days after ripening was initiated with ethylene. Effects of treatments with 1-methylcyclopropene (1-MCP), abscisic acid (ABA) and indole acetic acid (IAA) on activities of these hydrolases were measured in order to help elucidate their roles during banana ripening. Ethylene stimulated activities of all four enzymes, at best differentially. 1-MCP and IAA suppressed the ethylene effects. ABA stimulated activities of all hydrolases except polygalacturonase. ABA stimulation was most evident for pectate lyase. Thus ethylene plays a major role in up-regulating the activities of various cell wall hydrolases. In contrast IAA suppresses their activity. ABA can enhance softening with or without ethylene.     

Ethylene sensitivity and changes in ethylene production during senescence in long-lived Delphinium flowers without sepal abscission

We investigated changes in ethylene production, sensitivity, effects of ethylene inhibitors and levels of ethylene receptor genes to determine factors responsible for long-lived flowers in a Delphinium line ‘B-10’. Flower longevity of ‘B-10’ was clearly longer than that of the control cultivar ‘Bellamosum’, and sepals of ‘B-10’ did not abscise. ‘B-10’ did not show the climacteric-like ethylene production during flower senescence but constitutively produced ethylene from days 0 to 9. The ethylene inhibitors silver thiosulfate (STS) and aminoethoxyvinylglycine (AVG) extended flower longevity in both cultivars. Exogenous ethylene treatment did not affect flower longevity but did increase ethylene production in ‘B-10’. These results suggest that low sensitivity to ethylene is responsible for long-lived ‘B-10’ flowers, and may suppress climacteric-like ethylene production.     

Benzyl-aminopurine (BAP) treatments delay cell wall degradation and softening,improving quality maintenance of refrigerated summer squash

Round summer squash are harvested before reaching full maturity and even though they are highly perishable, fruit postharvest handling is mostly based on storage at non-chilling temperatures. Finding complementary treatments minimizing deterioration and reducing postharvest losses would be extremely useful. In this work we evaluated the effect of postharvest cytokinin (CK) treatments on refrigerated round soft rind squash. Fruit were harvested at commercial maturity and sprayed with 1 mmol L⁻¹ benzylaminopurine (BAP) or water (control) prior to storage at 5 °C for 0, 13 or 25 days. Quality was assessed upon removal from cold storage as well as after a 2 day shelf-life period at 20 °C. CK-treated fruit showed slower deterioration and dehydration and remained firmer than the control. BAP sprays did not affect color, respiration or sugar-acid balance. The treatments prevented phenolic compound accumulation, and decreased pectin solubilization. By the end of the storage period BAP-treated squash had higher levels (45%) of tightly-bound polyuronides than untreated controls, indicating a substantial delay in cell wall dismantling. CK sprays also reduced neutral sugar solubilization from pectin-rich fractions, but no changes were found in the cross-linking glycans or cellulose. To our knowledge, this is the first work showing that CK can regulate pectin disassembly in developing fruit. Postharvest BAP sprays preventing texture deterioration may be a simple treatment to complement refrigeration of round, soft rind, summer squash.     

Mode of action of abscisic acid in triggering ethylene biosynthesis and softening during ripening in mango fruit

The role of abscisic acid (ABA) in triggering ethylene biosynthesis and ripening of mango fruit was investigated by applying ABA [S-(+)-cis,trans-abscisic acid] and an inhibitor of its biosynthesis [nordihydroguaiaretic acid (NDGA)]. Application of 1 mM ABA accelerated ethylene biosynthesis through promoting the activities of ethylene biosynthesis enzymes (1-aminocyclopropane-1-carboxylic acid synthase, ACS; 1-aminocyclopropane-1-carboxylic acid oxidase, ACO) and accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC), enhanced fruit softening and activity of endo-polygalacturonase and reduced pectin esterase activity in the pulp. The activities of ethylene biosynthesis and softening enzymes were significantly delayed and/or suppressed in the pulp of NDGA-treated fruit. The ABA-treated fruit had higher total sugars and sucrose as well as degradation of total organic acids, and citric and fumaric acids compared with NDGA treatment. These results suggest that ABA is involved in regulating mango fruit ripening and its effects are, at least in part, mediated by changes in ethylene production.     

Role of the genes Md-ACO1 and Md-ACS1 in ethylene production and shelf life of apple (Malus domestica Borkh)

Shelf life determines the economic life time of mature apples, which can be either freshly harvested or stored. Good shelf life is highly associated with a slow decrease of fruit firmness at room temperature. Apple is a climacteric fruit, in which loss of firmness seems to be physiologically related to ethylene. Ethylenes biosynthetic pathway is controlled by two large gene families coding for 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxydase (ACO).In this study, one ACS and one ACO gene were examined for their effect on ethylene production and shelf life in apple using gene specific molecular marker, and have also been positioned on a molecular marker linkage map. The ACO marker was developed in this research and mapped on linkage group (LG) 10 of the crosses Prima × Fiesta and Fuji × Mondial Gala, within the 5% border of a previously identified fruit firmness QTL [Theor Appl Genet 100 (2000) 1074]. We denoted this locus as Md-ACO1. In addition, we mapped the previously developed Md-ACS1 marker [Theor Appl Genet 101 (2000) 742] on LG15.Studies on the cross Fuji × Braeburn revealed that Md-ACS1 and Md-ACO1 independently affect the internal ethylene concentration (IEC) as well as shelf life of apple, Md-ACS1 having the strongest effect. Descendants homozygous for Md-ACS1-2 and Md-ACO1-1 showed to have the lowest ethylene production as well as superior shelf-life. These two genes are candidates to be included in marker assisted breeding.     

Effect of 1-methylcyclopropene (1-MCP) treatment on sweet basil leaf senescence and ethylene production during shelf-life

The effect of 1-methylcyclopropene (1-MCP) on shelf-life and postharvest quality of sweet basil detached leaves was examined. Treatment with 0.2, 0.4 and 0.6 g m⁻³ 1-MCP for 8 h was conducted at 15 °C in the dark. After the treatment the leaves were packed in polyethylene bags then sealed and stored at 20 °C. All 1-MCP concentrations significantly increased the shelf-life of leaves compared to the untreated control, and leaf weight loss with 1-MCP treatment was minimal. 1-MCP treatment significantly retarded the degradation of chlorophyll and protein content of detached leaves during storage and decreased leaf ethylene production. 1-MCP treatment also significantly retarded the decrease of volatile oil percentage in detached leaves during storage compared to the control. Among 1-MCP concentrations, 0.4 g m⁻³ resulted in the maximum shelf-life as well as improved postharvest quality of the leaves. The results clearly indicate that a single treatment with 1-MCP may provide a feasible technique for extending the shelf-life and maintaining higher volatile oil percentage of sweet basil leaves.     

Molecular analysis of softening and ethylene synthesis and signaling pathways in a non-softening apple cultivar, ‘Honeycrisp’ and a rapidly softening cultivar, ‘McIntosh’

A feature of ‘Honeycrisp’ apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] is that they maintain flesh firmness over extended storage. The objective of this study was to elucidate molecular mechanisms that are responsible for slow softening of ‘Honeycrisp’ as compared with a rapidly softening cultivar, ‘McIntosh’. Fruit from both cultivars were picked during the normal harvest period and stored at 20 °C for 10 d. Internal ethylene concentrations (IECs) in ‘Honeycrisp’ fruit were lower than in ‘McIntosh’, but at climacteric levels of ethylene ‘Honeycrisp’ fruit maintained their firmness over this period, while ‘McIntosh’ softened rapidly. Concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were higher in ‘Honeycrisp’ than in ‘McIntosh’ apples. qRT-PCR analysis was carried out for genes involved in ethylene biosynthesis, perception and signaling [ACC synthase (MdACS); ACC oxidase (MdACO); ethylene receptors (MdETR and MdERS); constitutive triple response (MdCTR); ethylene response factor (MdERF)], as well as those involved in cell wall metabolism [polygalacturonase (MdPG); xyloglucan endotransglucosylase (MdXTH); expansin (MdEXP); β-galactosidase (Md β-GS); arabinofuranosidase (MdAFase); pectate lyase (MdPL)]. At comparable IECs, the expression of genes involved in ethylene synthesis, ethylene perception and signal transduction was generally much higher in ‘Honeycrisp’ than in ‘McIntosh’ fruit. However, the expression of MdAFase and MdEXP3 was generally lower in ‘Honeycrisp’ than in ‘McIntosh’, while that of MdPG and MdPL was extremely low in ‘Honeycrisp’. Expression of MdPG1 was very low, even though IECs were at climacteric levels. Absence of fruit softening in ‘Honeycrisp’ is probably associated with restricted cell wall enzyme activity. The lower maximum IECs found in ‘Honeycrisp’ compared with ‘McIntosh’ do not appear to be related to expression of genes involved in ethylene biosynthesis.     

Phytoplankton primary production,chlorophyll and composition in an inlet of the Western Wadden Sea (Marsdiep)

From February 1974 to April 1976, estimates for in situ phytoplankton primary production in the Marsdiep tidal inlet area of the western Dutch Wadden Sea were made from incubator primary production data using a constant light source. Low values were estimated in winter with a minimum in January (average 0.016 g C·m⁻²·d⁻¹. Values increased rapidly from the middle of March during the spring phytoplankton bloom to a maximum in May (average 1.1 g C·m⁻² ·d⁻¹, maxima of 3 g C·m⁻²·d⁻¹ or more). During summer these estimates showed large short-term variations in in situ primary production from incubator data as well as in in situ measurements during 1 to 3 days in June and August in the years 1971 to 1979. This variability forms a problem in estimating annual phytoplankton primary production in the area. It also prevents a reliable comparison of the present estimate with earlier estimates of annual primary production based on fewer data (one per month or less). It is likely that also in other areas, in particular in coastal regions, similar difficulties in estimating primary production will be encountered.     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.     

Effect of 1-methylcyclopropene (1-MCP) on softening of fresh-cut kiwifruit,mango and persimmon slices

Ethylene production is enhanced by wounding during fresh-cut processing and the accumulation of this gas within the packages of fresh-cut fruit can be detrimental to their quality and shelf-life. The effect of 1-methylcyclopropene (1-MCP), an ethylene action blocker, applied before or after processing, on the quality of fresh-cut kiwifruit, mangoes and persimmons was evaluated during storage at 5 °C. Fresh-cut ‘Hayward’ kiwifruit slices softened at a slower rate and their ethylene production rate was decreased in response to 1-MCP application (1 μL L⁻¹ for 6 h at 10 °C) either before or after processing. A 2-min dip in 0.09 M (1%, w/v) CaCl₂ synergistically increased the effect of 1-MCP on firmness retention and 1-MCP did not affect the color (L* value) of fresh-cut kiwifruit slices. Softening and browning (decreasing L* value) were delayed when 1-MCP was applied directly on fresh-cut ‘Kent’ and ‘Keitt’ mango slices. Respiration rate of mango slices was not influenced by 1-MCP whereas the ethylene production was affected only towards the end of their shelf-life. Fresh-cut ‘Fuyu’ persimmons treated with 1-MCP after processing presented higher ethylene production rate, slower softening rate and slower darkening of color (decrease in L* value), whereas the respiration rate was not affected.     

Changes in spatial distribution of primary production,photosynthetic pigments and phytoplankton species composition during two surveys in the German bight

A grid of 61 stations was sampled twice in the German Bight. At all stations dissolved nutrients (Si, P, N), fluorescence, temperature and salinity were measured along the vertical at surface, 5 m, 10 m, and 10 m intervals till the bottom. At selected stations photosynthetic rates were measured with ¹⁴C method (both surveys) and pigment with a HPLC method (first survey). Phytoplankton species composition was dominated by small diatoms, mainly Leptocylindrus minimus, flagellates, both dinoflagellates and choanoflagellates and near shore blooms of Phaeocystis pouchetii. Primary production and chlorophyll-a showed a linear correlation (r=0.90, n=23). Primary production showed highest rates along the North and East Frisian islands, where phytoplankton was dominated by Phaeocystis and Leptocylindrus. These coastal stations were completely mixed whereas a large part already showed stratification due to salinity and temperature. Thermocline and pycnocline were at about 10 m depth. No differences in oxygen content of surface or bottom waters were observed. Silicate and phophate concentrations were very low whereas nitrogen still showed very high concentrations. Low hypolimnetic oxygen concentrations are only possible when transport of primary produced organic matter is transported to stratified regions later in summer. Rapid growth of blooms was observed within a weeks period. More primary production measurements in the German Bight should be done to allow for budget calculations of oxygen consumption below the thermocline.     

Antioxidant changes during postharvest processing and storage of leek (Allium ampeloprasum var. porrum)

The evaluation of the impact of postharvest processing and storage on the health benefits of vegetables is of great practical importance. Reports on their effect on the antioxidant capacity, polyphenol and S-alk(en)yl-l-cysteine sulfoxide (ACSO) content, i.e. isoalliin and methiin of the white shaft of leek (Allium ampeloprasum var. porrum), however, are limited. This study determined the levels of the antioxidant properties of leek from postharvest processing at the farm until refrigerated storage of 13 days at the consumer. Two cases were investigated, (1) leek sold as an entire plant and (2) leek with a large part of the green leaves removed, where the shafts are sold in a plastic package. The antioxidant capacity and the total content of phenolic compounds in the white shaft of the entire and packaged leek was stable during 13 days of refrigerated storage. A significant increase in the concentration of isoalliin was observed. Comparing the entire and processed/packaged leek, significant differences could be observed in antioxidant properties. The ACSO content in the white shaft of packaged leek was significant lower than the content in the white part of the entire leek. Therefore, the minimal processing step of cutting the green leaves and roots had an influence on the levels of antioxidant properties.     

Relationships between mineral content, lipoxygenase activity, levels of 1-aminocyclopropane-1-carboxylic acid and ethylene emission in apple fruit flesh disks (cv. Jonagold) during storage

Lipoxygenase activity (LOX), levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and of 1-malonyl-aminocyclopropane-1-carboxylic acid (MACC) and the capacity of isolated fruit disks to evolve ethylene were examined during storage of apples having different fruit mineral content. The internal ethylene concentration (IEC) of the whole fruit was also measured before removing discs of tissue. The results show that all these activities depend on the fruit mineral content and confirm general knowledge on the relations between minerals and fruit storage. For instance, fruits rich in calcium and/or phosphorus presented a lower LOX activity, a lower ACC content and a lower ethylene emission while fruits rich in potassium and/or with a relatively high K/Ca presented a higher LOX activity, a higher ACC level and a higher ethylene emission. Results are discussed in an attempt to explain the effects of minerals on storage quality.     

Chemical and physiological changes of phytoplankton during the spring bloom,dominated by phaeocystis pouchetii (Haptophyceae): observations in Dutch coastal waters of the North Sea

During the spring bloom of phytoplankton in Dutch coastal waters of the North Sea the flux of ¹⁴C-labelled products into pools of protein, polysaccharides, small metabolic intermediates and lipids was studied. The molecular size distribution of extracellular products, amounting to 28% of the particulate production, was determined by gel filtration. Concentrations of protein and carbohydrates were determined in the same phytoplankton samples. At an early stage of the bloom protein synthesis and protein concentration dominated over carbohydrate synthesis and carbohydrate concentration, but after the peak of the bloom carbohydrates were the predominant photosynthetic endproduct. These observations have been compared to similar observations on unialgal cultures of Phaeocystis pouchetii. The influence of phosphate depletion on the extracellular release of organic compounds and the impact of the colonial growth form of Phaeocystis pouchetii on the distribution of intra- and extracellular labelled compounds are also discussed.     

Nutritional status and pigment composition of phytoplankton during spring and summer Phaeocystis blooms in Dutch coastal waters (Marsdiep area)

The general nutritional status and pigment composition of the phytoplankton population during the 1991 spring and summer Phaeocystis blooms in Dutch coastal waters was analysed using the 480/665 nm absorption ratio of 90% acetone extracts as well as reverse-phase HPLC-pigment analysis. A 100% increase in this ratio was indicative of moderate nutrient deficiency at the end of the Phaeocystis spring bloom in the Marsdiep area. During the summer, nitrate was more likely to be the limiting nutrient than phosphate. Both physiological adaptation and species composition were found to influence the absorption ratio. Variations in the absorption ratio did not completely reflect the variations in fucoxanthin and chlorophyll a. Therefore it was concluded that besides nutrient limitation dynamics, the variable abundances of in particular chlorophyll-c3 containing species (such as Prymnesiophyceae) may effect the absorption ratio.     

Traditional seed production in landraces of daikon (Raphanus sativus) in Kyushu, Japan

Landraces of daikon, Japanese radish, Raphanus sativus var. hortensis, are grown and used traditionally in Kyushu, Japan. These landraces are maintained by seeds harvested from selected plants which are transplanted as dormant tap roots or are retained in a portion of field. Seeds kept in intact siliquas on the stems are harvested and stored until use, by hanging the dried stems. Although the relatively small number of plants used in a patch for seed production might be expected to result in a narrow base of genetic diversity of a farmers' lot in a landrace, addition of a few plants with contrasting features, pollen exchange between household patches, and contamination from other cultivars and feral forms may save the landraces from the rapid loss of diversity and deterioration caused by inbreeding depression. The seed production by transplanting described in medieval Japanese literature is relatively similar to the current practice. The factors responsible for maintenance of the landrace together with the cultural and climatic diversity of Japan may have contributed to a high diversity of landraces of the daikon. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of exogenous ethylene during refrigerated storage on storability and quality of Actinidia chinensis (cv. Hort16A)

The kiwifruit industry was established on fruit of Actinidia deliciosa (‘Hayward’), which is known as a climacteric fruit with high sensitivity to ethylene. In recent times fruit from Actinidia chinensis have become a substantial component of the kiwifruit market. There is limited information about the sensitivity of A. chinensis to ethylene during refrigerated storage and hence current ethylene management practices for A. chinensis mimic those established for A. deliciosa. This research aimed to quantify the effect of ethylene during refrigerated storage on A. chinensis (‘Hort16A’) quality (firmness, colour and total soluble solids). Three grower lines were stored at 1.5 °C, 95% RH with ethylene in the range of 0.001-1 μL L⁻¹ applied to the environment after 3 weeks of storage for the remainder of storage (17 weeks). Fruit quality was assessed at regular intervals. Loss of firmness was found to be very sensitive to ethylene, with significant differences between fruit stored in 0.001 μL L⁻¹ (as a control) and 0.1 μL L⁻¹ occurring after 2 weeks of exposure. Fruit exposed to 1 μL L⁻¹ ethylene not only rapidly softened, but also increased in hue angle (greenness) and reduced in lightness (darkened) further reducing the quality of the yellow coloured kiwifruit cultivar. Total soluble solids were not heavily influenced by ethylene exposure, with grower differences being maintained throughout the experiment. This work demonstrates that A. chinensis (cv. Hort16A) fruit firmness and colour will be influenced by the ethylene conditions in a commercial storage environment by advancing ripening and senescence.     

Current status of tropical fruit breeding and genetics for three tropical fruit species cultivated in Japan: pineapple,mango, and papaya

Tropical fruit crops are predominantly produced in tropical and subtropical developing countries, but some are now grown in southern Japan. Pineapple (Ananas comosus), mango (Mangifera indica) and papaya (Carica papaya) are major tropical fruits cultivated in Japan. Modern, well-organized breeding systems have not yet been developed for most tropical fruit species. Most parts of Japan are in the temperate climate zone, but some southern areas such as the Ryukyu Islands, which stretch from Kyushu to Taiwan, are at the northern limits for tropical fruit production without artificial heating. In this review, we describe the current status of tropical fruit breeding, genetics, genomics, and biotechnology of three main tropical fruits (pineapple, mango, and papaya) that are cultivated and consumed in Japan. More than ten new elite cultivars of pineapple have been released with improved fruit quality and suitability for consumption as fresh fruit. New challenges and perspectives for obtaining high fruit quality are discussed in the context of breeding programs for pineapple.     

Maternal inheritance of cytoplasmic organelles in intergeneric hybrids of Carica papaya L. and Vasconcellea spp. (Caricaceae Dumort., Brassicales)

The mode of inheritance of chloroplast and mitochondrial DNA has been determined in intergeneric hybrids between C. papaya and four different Vasconcellea species by employing a restriction fragment length polymorphism analysis of a PCR-amplified chloroplast and mitochondrial DNA region. Artificial F₁ hybrids were produced between a female specimen of C. papaya and male specimens of either V. parviflora, V. goudotiana, V. cundinamarcensis or V. quercifolia. The hybridization patterns of all hybrids correspond in all cases with that of the C. papaya mother, and are different from that of the paternal Vasconcellea species, thus indicating the maternal inheritance of cpDNA and mtDNA in intergeneric hybrids between C. papaya and wild relatives of the Vasconcellea genus.